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6v Gauges To 12v

6v Gauges To 12v Starter Solenoid

12v Radio In 6v Vehicles

6 Volt Tach

6 VDC Radio Source

6V Generator


Ballast Resistor

FOMOCO Alt/V-Reg Wiring Assist

Ballast Resistor For 62 Pickup

Jump Starting A 6v With A 12v

Starting The Engine Using A Battery Charger

6 Volt To 12 Volt

12-Volt Points And Condenser For L-134


 Why not to run 6 volt motors from a 12v source



MVP The Herb Farm wrote: Jerry: Since you are a retired Electronics Design Engineer from the DELCO Electronics Division, do you think it would be possible for you to give us wagon and pickup guys a lesson on how to convert our original 6 volt gauges over to 12 volt and have them read accurately. I've heard from others that it can be done but I'm not really good with electronics Any help or suggestions would be appreciated. Thanks for all your great posts!!

Mark Usnick responded: When I converted my CJ5 to 12V, I got some good tips from Eric Lawson (met him on classicjeep). He has a very good write-up at

The one thing his article was missing was a way to run the old 6V guages in the new 12V system. I recently stumbled across an excellent writeup on how to build 12V to 6V voltage regulators of different capacities. It's a top-notch article. Check it out at:

Scott Little wrote: The web page below (6to12to6) is similar to a voltage regulator recipe I got from Willys Works in Tucson. However mine is simpler and does not use the capacitor or transistor or diode or heatsink. Maybe that is why my temp gauge does not read correctly. Guess I better try again and see what happens. That is a very good write-up, I don't really know what any of it means but I can probably duplicate it without any trouble.

Jerry Adams responded: I checked out the above site, and it is a darned good one. I did not know that Radio Shack Carried the 7806 part. I chose the LM317T instead, and made it a 6V part by adding the resistors. I made my unit several years ago, when Radio Shack didn't carry the 7806, so I worked around it with parts they had.

The man's deigns are simple and sound, although he does not provide any "load dump" protection. "Load dump" is a term that stands for the serious voltage spike and oscillations that occur if the load is suddenly removed from an alternator. A load dump can reach up to about 50 volts, and occurs when a heavy load above about 50% of the unit's rated output is suddenly removed from an alternator. This is due to the fact that the internal regulator has had the alternator's field coils energized to a level that will sustain the required high output. When the load has been suddenly removed (say a fuse blows), it takes a finite time for the regulator to detect the fact that the load is no longer present and compensate. During this time, the output of the alternator rises dramatically. The exact amount of the rise will depend on several things including: the state of charge and overall condition of the battery; the quality of the connections in the circuit, particularly the ones between the battery and the alternator; the wire gage, quality of connections, etc. between the component that "dumped" and the other components in the system; the relative location of the component in question in the vehicle's wiring system; and lots of other rather obscure things.

Because most solid state electronics components will fail very quickly (on the order of a few 1/1,000,000's of a second) if subject to too much voltage, GM found it necessary to incorporate load dump protection in all solid state devices that are connected to the vehicle's 12 volt system.

I would use a different transistor in the high powered rig, as the transistor he chose is in a TO-5 case and is a bit awkward to mount when compared to the much more simple TO-220 type case. Other than that, I like what he has. Because there are so many variables involved with "load dump," you may well be able to just build what he has designed and use it for years without any troubles. On the other hand, many jeepers like to install lots of high current equipment like winches, off road driving lights, etc., so the chances of such equipment creating a load dump are proportionally greater than would otherwise be the case...

Jerry Adams wrote: I don't know what kind of gages you have on your vehicle, but in my CJ2A, the temperature and oil pressure gages are mechanical. The ammeter doesn't know or care about the difference between 6 volts and 12 volts, so the only gage that needs converting is the gas gage. This gage draws about 0.8 amps max, so I designed a simple solid state regulator that clamps the output voltage at 5.89 volts. I put it in a small plastic case which mounts on the firewall. It requires only a hand full of components, all of which are available at Radio Shack:

1 ea. Small plastic experimenter's box with cover

1 ea. Short fuse holder

1 ea. 1.5 A. Fuse

2 ea. 15 volt Zener Diodes

1 ea. LM317T Voltage Regulator

1 ea. 220 ohm resistor

1 ea. 1,000 ohm resistor

1 ea. 4,700 ohm resistor

1 ea. "TO-220" Mounting Kit

1 ea. "TO-220" Heat Sink

1 ea. Small Piece of "Vector Board."

4 ea. 4-40 X 3/4" screws

12 ea. 4-40 nuts

12 ea. #4 flat washers.

Not absolutely necessary, but it makes a more professional looking unit:

1 ea. 4-screw terminal strip

2 ea. 6-32 X 1" screws

2 ea. 6-32 nuts

4 ea. #6 flat washers.

#18 gage insulated wire to make connections to the "outside world." If you use the terminal strip, you will need about a foot or so. If you decide to wire the box directly to the fuel gage, you will need enough wire to run from where ever you mount the box to the back of the fuel gage.


Small soldering iron

Small spool of Rosin Core solder

Small needle nose pliers

Small diagonal wire cutters

Small screwdriver

Small crescent wrench or a good pair of pliers

Drill and a couple of bits.

Hack saw to cut a small section of the vector board.

The construction is definitely *not* rocket science, and should be well within the capabilities of any of you. I put mine together in one leisurely evening working at the kitchen table. If you are interested, e-mail me privately, and I'll whip up a set of "plans" and snail mail them to you. I made my unit a bit more fancy with an "LED" to tell me it's working, and some serious "Load Dump" protection (more than I have provided in the above parts list), but that is not necessary.

It's been a while since I built it, so I really don't remember the cost, but I think that it should run about $10 to $15:

Box and other hardware - about $5.00

LM317T, heat sink, mount kit - About 5.00

Resistors, Zeners - about $3.00

Vector board - About $3.00

The above prices are strictly guesswork.

If I get any interest, I'll go down to Radio Shack and get exact Part Numbers, Prices, etc. and include them in the plans...

Joseph Dante wrote: Jerry, I definitely have an interest. I would have no trouble with the assembly either. I just read your reply to the other design and am of like mind that the load dump protection is a good idea. Is it possible to incorporate the newer-easier components into your design. In addition is it possible to "load dump" protect the system as a hole or dose the same characteristic that precludes the regulator in the alternator from catching it, prevent one device cure all approach. It sounds to me as if you are the man for the job. :) Thanks in advance for your time and trouble.

Jerry Adams wrote: It is possible to make a filter that will catch a load dump for the entire system, but not necessary. All modern (made during the last 10 years or so) automotive electronics gizmos have load dump protection incorporated in the design, or at least they will unless made in lower boonkdocia by conscripted high school dropouts. The other stuff, like lights, motors, etc. can withstand a load dump. A typical load dump pulse lasts for about 20 to 30 milliseconds, which is not long enough to do much damage to them. It is the transistor's intolerance for even extremely short periods of over voltage that causes the problem with solid state devices. It is much easier and cheaper to provide the protection as needed.

The LM317 is an old design component. I chose it because (1) Radio Shack carries them; (2) The design is proven, stable and rugged; and (3) the LM317 was good for about 1.5 amps, which gave me some margin. There are several voltage regulator chips that have been specifically designed for automotive applications. For example, the LM2940 Voltage Regulator chip made by National Semiconductor has 60V Load Dump, Reverse Battery protection, Short Circuit protection and Thermal Limit protection **built into the chip***. I don't know how available they are, but an LM2940 would make designing (and building) a 1 amp, 6 volt supply a breeze.

Would work just fine to run a fuel gage. You could add the bypass transistor shown in the schematic for the web site to get more current, but you would need to either choose a transistor that could stand 60 volts, or provide load dump protection for it. The above is so simple to make, I would tend to make a separate unit for each gage. You can also make a supply that would allow you to use one of the old 6V radios if you want to keep it, but I would be much more inclined to install a modern radio. I love classical music which almost has to be in stereo, and I like FM much better than AM, so I would want a more modern radio. However, to each his own in that regard. I'll look into the availability of the LM2940. If they are easy to find, that would be the way to go. I designed my unit in the mid 1980's, and the LM317 was the best component I could find at Radio Shack back then.

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? wrote: I am rebuilding a '62 willys pu. i recently converted it to 12v from 6v. my solenoid on the starter keeps emitting smoking after small increments of starting(10 to 15 sec). I thought at first that maybe i wired up my maxi fuse wrong. but now i am being lead to believe that it maybe a 6v or just very old? either I should replace it with 12v.

Jerry Adams responded: Your solenoid is telling you that it's a 6V unit and doesn't particularly like working on 12 volts. Yes, by all means, install a 12 Volt unit. By the way, there are two problems associated with using a 6V starter on a 12V system:

1. The starter will get hot real quick if you "grind" on it, and there is a very real possibility you could burn it out.

2. There is a very real and serious danger that a 6V starter motor can literally over-rev itself and fly apart if it is allowed to run unloaded on a 12V system. This can happen really easily if your Bendix drive fails to engage the gear on the flywheel, or the Bendix unit breaks a shaft. Not good!

I strongly urge you to either buy and install a 12 Volt starter motor, or have a set of 12 volt field coils installed in your old unit. The 12V field coils will not do much to keep it from overheating, but should prevent the unit from over-revving and destroying itself. I had the 12 Volt fields installed in the starter on my '2A when I converted it over to 12 volts.

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? Wrote: Hey Group, Took my truck down the road aways to a VW resto place to see if I could get my

hands on a Blaupunkt 6 volt radio.

The female laughed at me, which takes a certain amount of guts considering I am 6' 2" 240 lbs. She says that every 6 volt Bug she could ever remember seeing did not have a radio at all. Her mechanic did recommend radio shack for a voltage booster.

This way, I could run a modern 12 volt radio off my 6 volt system.

Jerry Adams responded: This is the way I would go. For one thing, all of the 6 volt radios I have seen used vacuum tubes and a "vibrator" power supply to make the high (about 150 volts) voltage needed for the plates. You can still get several varieties of tubes, but I don't even begin to know where to start looking for a vibrator. A more modern radio would have FM, a tape deck, and other goodies.

? Wrote: Jerry, as poor of a mechanic as I am, I am a frighteningly bad electrician. (If there are three wires, I will hook em up wrong 4 times, and by the time I get em right, the components are fried)

Jerry wrote: Dear me! Well, take heart! I was in the middle of the 7th grade before I could convince my body to do a "Jumping Jack." If you want to see something humorous, watch me try to drive a screw with my left hand... The point is, that, just as we are "all good at something," most of use are also *bad* at something as well. Good thing too- can you imagine what would happen if we were all good at the same thing, and bad at everything else? We would have a world with damn good pretzels, but lousy beer!

? Wrote Is there such a thing as a voltage booster? If so, can you give me the Neanderthalian intro briefing?

Jerry wrote: OK- In plain English, yes, there are ways to boost a DC (Direct Current) voltage. For example, one could design a transistorized circuit to switch the input (say 6 volts) on and off several thousand times per second. If you fed this switched power through a properly designed transformer, the output would be a higher voltage version of the chopped up input. This could then be "rectified," or converted back to DC. Add the necessary components to stabilize and smooth up the output, and viola! 12 volts made from 6 volts. The "vibrator" I mentioned in regard to a 6 volt radio is a mechanical switch that is used to chop up the input voltage, which is then fed to a transformer, rectified, filtered, and used to supply the high voltage DC needed to run the vacuum tubes. They used a mechanical chopper because there were no transistors back then, and while it was possible to make an electronic chopper, they would need to employ a vacuum tube, which would require the high voltage DC they were trying to make in the first place.

Not having transistors (and their cousins, the solid state diode) around forced many designers to look to mechanics to solve electrical problems. Another example of a mechanical solution to an electrical problem is the commutator found on all early automotive generators. The commutator functions as a mechanical "rectifier" to force the output of the generator to always have the same polarity. Without a commutator, the output would be AC, just like the power in your house, but at a varying frequency that depended on the RPM the generator was running at.

An Alternator is also inherently an AC device, but a bank of solid state diodes converts the output to DC. With no diodes around, the "folks back then" came up with a very clever mechanical solution to the problem of converting the AC to DC in a generator. By the way, one of the big reasons why Alternators are so much more efficient than generators is that it becomes exceedingly complex to have more than one set of brushes in a small space. This means that the ordinary automotive generator has only one set of brushes, which means that only one set of windings can be connected to them at a time. Also, the power creating windings of a generator must be connected to the commutator. Because they need to be wound of relatively heavy wire to carry the current, the windings are relatively speaking heavy. This creates some interesting mechanical problems due to the centrifugal forces acting on the moving armature (more correctly referred to as the "rotor") of the generator. The field windings, which produce the magnetic field required for the generator to make electricity don't run through the commutator, and are fixed to the side wall of the generator housing, where they are referred to as the "stator."

In an alternator, the rectification is done by a set of diodes, rather than the mechanical switch of the generator. This means that more than one set of windings can be employed, which makes the entire system more efficient and compact. Also, the power producing windings can become the "stator" and are fixed inside the body of the alternator. The field windings become the rotor, and are wound into the moving part of the alternator. You still need a brush assembly to get the power to the field coils in an alternator, but because the current is a lot lower, and no rectification is needed, the large brushes and commutator in a generator are replaced by much smaller brushes working on simple continuous contacts called "slip rings." For various reasons, it is easier to design and manufacture the rotor of an alternator so that it will withstand the mechanical forces created when it is spun rapidly. If you have both a generator and an alternator side by side, you will notice that the pulley on the generator is larger than the pulley on the alternator. This means that, for a given engine RPM, the alternator will be turning faster than the generator. This allows the alternator to put out more power at a lower RPM than a generator can.

Jerry Adams wrote: OK- Here's the *simple* way to do it- Look in the JC Whitney catalog (yes, I know...). On page 32 of their latest (I think catalog we find:

"Operate your 12V Negative-ground Accessories in Vehicles with a 6V or 12V Positive or 6V Negative-ground System!

"*A must when you want to use newer accessories (radio, CD player, radar detector, mobile phone) in your older or 'classic' vehicle.

"Converter is small enough (a 1-3/4" cube) and light enough (about 9 oz) to fit neatly, easily on the accessory it serves, behind your dash or in any other convenient spot. Uses common ground - no isolation required. Reverse Polarity, overload and short-circuit protection. Low (10mA) no-load current minimizes draw on battery when an alarm system or radio/clock with memory is in use. NOTES: Check continuous and peak power requirements before ordering. (1) With your vehicle's 6V input and these inverters/converters, a high-output 12V sound system may perform effectively at low volume, but not for extended periods beyond the converter's stated capacities. (2) Weak batteries, malfunctioning electronics systems and poor connections lower capacities. NOT RECOMMENDED FOR: Power-actuated door locks, trunk release solenoids, air conditioner clutches, fans, blowers, power windows or other electro-mechanical devices."

They list two choices for running a 12V radio from a 6V Positive ground system:


Catalog Number Capacity with 4 to 16V input Price

81NF4988U 26.5 Watts - 2.1 amps @ 12.6V $89.99

81NF4989B 16 Watts - 1.3 amps @ 12.6V $59.99

and two choices for running a 12V radio from a 6V Negative ground system:


Capacity with 5V to 8V input

81NF3904B 30 Watts - 2.5 amps @ 12.6V $89.99

81NF3905R 18 Watts - 1.5 amps @ 12.6V $59.99

So, there you are - yes, you can run a modern radio from your 6V jeep. Are the above items any good? I haven't a clue! My experience with JC Whitney goes back a long way, and I find their products to be a mixed bag. Some good stuff, an occasional clunker. Back in the late 60's I purchased two 6V "universal" electric wiper motors for a 1954 Dodge WM300 "Power Wagon" from JCW, and one worked great, the other did not - JCW replaced the defective motor, and it worked fine. 20+ years later, I bought two more of the same motors (as best I could recall, they looked identical to the earlier units!) for my CJ2A when I converted it over to 12 volts, and both of them work great. So, you pays you nickel and you takes you chances.

If the Negative post of your battery is hooked to the chassis, you have a Negative ground system. If the Positive post is hooked to the chassis, you have a Positive ground system. I am pretty sure that all early jeeps were Negative ground, but check to make sure before you order. If it were me, I would go for the higher capacity unit. I think that most simple-minded car radios pull about 12 watts, so they would work OK with the lower power system, but I am a big believer in not running equipment flat out, so I would go for the bigger unit. Besides, who knows when a little extra 12V might come in handy?

Can you build one yourself? Yes, but you would probably find that the cost of the components is greater than what you would pay for the above units, plus you would have to deal with the packaging, etc.

I hope this helps you!

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Richard Grover wrote: Good numbers. Where did you find a tach? Are you 12V? I looked for a 6V tach but all I could find were 12V tachs. I don't know what difference it makes, but the people at the parts stores didn't think a 12V tach would work with a 6V system. I know I can do the whole voltage conversion in electronics, but it seemed like a lot of work for a tach. How about an electrical engineer explaining to us why a 12V tach will or will not work with 6V?

Glenn Goodman wrote: Same for 24 volt. It's been fun trying to find anything at all for a 24 volt system and I sure would like to find a tach for it. Any ideas/suggestions/ solutions?

Hasty, Matt wrote: Hello peoples, There is a place in CA that specializes in restored tachs. It's called;

Palo Alto Speedometer718 Emerrson Street Palo Alto. CA 94301

650-323-4632 or 650-323-0243 Speedometers, tachometers, clocks, gauges, restored, calibrated.

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Dan wrote: OK. I asked one of the big shots connected with West Coast Willys to keep his eyes open for a stock 6 volt dash radio at the 5th annual Willys Meet at Toledo. I said I would pay up to $75 for an operational one. He said they are extremely hard to find, ranging in price from $200-$700 bucks, the priciness based on the smart Willys logo on the dial face. OK, I'm still going to try a Blaupunkt if I don't have to carve the dash too badly.

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? Wrote: How can I test if my generator is working!?

Jerry Adams wrote: The first, and most obvious step is to carefully inspect ***all*** of the wiring running between the generator, voltage regulator, ammeter, and battery. Make absolutely certain that the insulation is good, and all connections are clean and tight. This will involve no little amount of effort, as you should check the entire circuit, including the connections to the ammeter! If you find any hint of bad insulation, it is best to replace the wire!

If this doesn't cure the problem, you have to check out the charging system: There should be two posts on your generator. One is marked "F" or "FLD" and the other "A" or "ARM". Assuming you have a reasonably accurate volt-ohm meter:

1. With the engine running at about 2,000 RPM (use your hand throttle, be sure to block the wheels!), measure the voltage between the "A" terminal and ground. If the generator is working OK, it should be between 7.2 to 7.6 volts with a good battery. A low battery may pull this reading down to about 7 volts or so, but it should come up to about 7.3 volts once the battery charges. A voltage much less than 7.2 with a charged battery may not be high enough to keep the battery fully charged. A voltage much above 7.6 volts will "boil" the water out of your battery - note: I use the term "boil" in the sense that my father used it. The true reaction is you are electrolyzing the water into hydrogen and oxygen. However, the terminology dad used conveys the sense of what happens, ie the water goes away.

2. If the generator is putting out and the voltage is within the above ranges but the battery keeps "running down" (another Dad term), you may have a partially sulfated battery (can't take a full charge) or bad connections to the battery posts, starter motor, etc.

3. If the generator is putting out but the voltage is out of the above ranges, the chances are pretty good that the generator is OK, but the regulator is shot. Advice: Don't mess around trying to repair the old regulator. Get a new one.

4. If the generator is at the battery voltage during the above test (about 6 volts, give or take), it could be one of several things:

(A) The voltage regulator could be bad. Get a piece of about 14 gage wire, and temporarily attach one end to a good ground. Connect your volt meter to the "A" post and ground and position it so you can read it. With the motor running at about 1,000 RPM, ***CAUTIOUSLY*** touch the wire from the battery to the "F" post on the generator. If you draw a sizable spark, and you see the volt meter jump, replace the regulator. (CAUTION: this test will cause the generator to go to maximum output. DON'T LEAVE THE WIRE ON THE TERMINAL FOR ANY LENGTH OF TIME. Just spark it and look for the volt meter to react. A much safer test involves making up a socket with a 60 watt 110 volt light bulb and some suitable wires. Remove the wires from both posts and tape them up. Attach one of the wires from your test light to a good ground. Attach the other wire from the test light to the "A" post. Ground the "F" post to a good ground. Start the motor and observe the light. It should begin to glow at about 1,500 RPM if the generator is good. If it does, replace the regulator.

(B) The generator could have a problem. If the above test does not cause the voltmeter to kick, or it fails to make the 60W bulb glow, you could have an open field or the brushes could be worn out. Shut off your motor, and remove both wires from the generator (be sure to label them so you can get them back right later on).

(1) Measure the *resistance* between the "F" terminal and the "A" Terminal It should be somewhere around a half an ohm. In practical terms, a reading near zero is OK. If you get very high resistance, the fields could be open.

(2) Measure the resistance between the "F" terminal and the frame of the generator. It should be very high (greater than 100,000 ohms.) If it is low, the field circuit is shorted.

(3) Inspect the brushes for excessive ware. Note: This is the cause of about 95% of generator failures. It is easiest to remove the generator from your vehicle to do this. Once you have it on the bench, remove the dust cover (it's a band of thin steel that is held in place by a clamp screw) from the Brush inspection slots. Use a wire hook (an old coat hanger can be bent to make one) and lift the brush tension spring, and then gently lift the brush out of the holder by pulling on the braided lead. The brush should be at least a half an inch long. If it is shorter than that, you will need to replace them. If you need to replace the brushes, it is best to disassemble the generator and check the commutator for ware. The commutator is the arrangement of copper bars with lots of heavy wires soldered to them. To disassemble the generator:

[1]. Remove both brushes and temporarily hold them and the springs out of the way by pulling the brushes partially out of the brackets and lowering the spring down on the side of the brush to clamp the brush between the spring and the side of the bracket.

[2]. Remove the two long bolts that run entirely through the generator.

[3]. Using a screwdriver and a small hammer, gently separate the back cap of the generator from the body. Note: You should work from side to side, as there is a bearing in the cap that supports one end of the armature.

[4]. Use the screwdriver and hammer to gently separate the front cap from the case. Pull the armature and the front plate assembly out of the generator body.

[5]. Remove the brushes from the body. Be careful not to loose the screws.

[6]. Remove the nut from the shaft that holds the pulley on the shaft, and remove the pulley. Be careful not to loose the key that fits between the shaft and the pulley!

[7]. Slip the front end plate off of the shaft. You will now have the armature free so you can work on it.

[8]. Inspect the commutator. If it is rough or worn, it should be turned in a lathe. It is best to let a good automotive electric shop do this for you, as you can do some serious damage to the commutator if you don't know what you are doing. While you have the armature in the shop, have them test it on a "growler."

[9]. Inspect the field coils (they are inside the housing, or body) for damaged or broken wires, or chaffed insulation. They can be replaced, but it takes a considerable amount of effort with a ***BIG*** screwdriver to remove them from the body. This is also a job for the good people at the auto electric shop. Not that you can't do it, just that they have the tools.

[10]. Inspect the bearings. To remove the front bearing, remove the screws from the bearing retainer, remove the retainer with the front felt washer. After that, press out the bearing and the back felt washer. The rear bearing is pressed into the rear cap, and is usually replaced by replacing the cap. It is good for a lot of miles, as it gets relatively little ware.

[11]. Test the brush holders for shorts to ground. Measure the resistance between each holder and the body. The resistance should be above 100,000 ohms.

[12]. Inspect the brush holders and springs for distortion, bent or cracked parts, etc.

[13]. Clean everything in diesel oil or solvent, and blow dry.

[14]. Reassemble in the reverse order. When you install the front bearing, pack it about half full with a high quality multi-purpose grease. Put a bit of grease inside the back bearing, but do not use too much or it will get into the commutator/brush area. A thin coat is sufficient. You will have to turn the front bracket until the little dowel pin lines up. Install new brushes, even if the old ones look OK. As long as you have gone this far, you might as well replace the parts that are the most likely to fail. Be careful when poking the bolts through the body so that you don't damage the field coils.

After you reinstall everything, you will have to "polarize" the generator. Use a piece of 14 gage wire, and briefly touch between the "B" or "BAT" and "A" or "ARM" terminals on the voltage regulator. You should draw a spark. One second is long enough.

? wrote I have no voltage out of my generator post to ground. I first referenced my battery which read 6.11 volts ( and yes I am using a true RMS Fluke meter). Sound like new generator time.

Jerry Not necessarily. Most generators can be repaired, no need to think about new. Also, you can have a bad regulator. Oh, I forgot to add one thing to check to the list. Be sure that the base of your regulator is well grounded... A little rust there can really mess things up!

Rick LeBlanc wrote: These tests are from my service manual:

1) Disconnect the generators armature cable at the regulator. Connect one lead of your voltmeter to the regulator terminal marked "armature" and with the engine running, ground the other lead. You should get 6v or near.

2) Or, if you have an ammeter, remove the armature and battery leads from the regulator and connect your ammeter between them. Remove the "field" lead from the regulator and while operating at idle speed, touch the field lead to the regulator base. Increase the speed noting the charging rate (do not exceed rated output of the generator). The generator is bad if the output will not build up.

3) Here's another way. Disconnect the "field" and "armature" cables at the generator. Connect a wire from the "field" terminal to ground and use a 60 watt, 110 volt test light to ground out the "armature" terminal. The light should glow at 1500 rpm, if you haven't electrocuted yourself first.

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MVP The Herb Farmwrote: I will be replacing the wiring in my '53 Wagon when it comes back from the paint shop. The cloth wiring is shot, and I don't want to start any forest fires. Anyone know where to get these clamp-on bulb contacts? I could use shrink-wrap on the old terminals and splice 'em to new wire but some of them are corroded beyond rehab. Any ideas?

Bernie Daily wrote: Get a catalog from Rhode Island Wiring Service 401-789-1955. You'll swear someone sent you a Christmas Catalog!

Jerry Adams wrote: I have run into the same problem. I tried several things.

(1) Salvaging the old contact by prying it open with an awl... Not much success.

(2) Making my own from 1/4" brazing rod using the file and drill press technique. They work great, but it is pretty time consuming. A lathe would make short work of it, but a file takes forever, as the teeth keep getting loaded up by the brass.

(3) Buying a replacement insert at the local parts store and splicing it onto the feed wire. This proved to be the method I used for Jenifer, although it is not very authentic looking.

If you are doing a true restoration, you will have to look for an original wiring harness with the sockets in place. If you are only looking to make your jeep drivable, I would go with the replacement socket insert spliced onto a new feed wire. By all means replace the old wiring. It is probably insulated with a natural rubber compound that gets very brittle with age.

While we are on the subject of wiring, watch out for the &(*&^$%^$#%*&^ modern sockets. Unlike the old types which are plated brass the new ones have some sort of plating over a steel shell. I have a utility trailer that I made several years ago that sits in the driveway. We toss big tree trimmings, etc. into it. When it gets full, I cart it to the local dump. I have had to replace two sets of tail lights when the sockets rusted too badly to make good contact any more. And, no, they aren't "El Cheapo" fixtures - I try to buy Grote' if I can find them - they seem to be slightly better made than the average parts store units. ARRUUGGGGHHHHH! There, I feel better now.

Mitch Utsey wrote: There is a type of grease used in electronics that will solve that problem. Unfortunately, I do not remember what it is called.

Jerry Adams wrote: I think you're thinking (hummm... awkward construction) of Silicone Heat Sink Grease. It's used to mount transistors, etc. Yes, it would work. So will a dab of any soft grease like the Lubriplate that comes in a tube. Unfortunately, I got lazy and didn't bother to take the cover off of the new fixture and lube the bulb. Big mistake. I did lube the third set of sockets, and they have lasted for over five years now. Still makes me mad that, even though I would be willing to pay the difference, I can't buy a fixture with decent sockets in it. I have found that there are solid brass fuse holders and sockets available at a local marine hardware store. Santa Barbara is on the coast with a man made harbor and lots of yachts, so there are three marine hardware stores down by the waterfront. I pay more, but I like the quality. I wish I could find the same type of stuff at my friendly local parts store.

Dave Blackmon wrote: I be bettin' this is dielectric grease......

Bernie Daily wrote: Any NAPA story has it.

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William Cunningham wrote: Please tell me more. Sounds like I am about to BTDT... and would rather not. What would be the resistor of choice (part #) for a F4-134 engine (57 FC-150). I have been running it a little with a 12 volt battery even though the bulbs tell me it is set up for 6 volt.

Rick Stivers wrote: Willy, I have found that the resistor from any 70s era Chrysler works well because it is not built into the wiring. I don't know the proper ohms (although I'm sure someone will supply that to us soon) or part number. The Chrysler resistor can be easily mounted and replaced upon failure. If you are searching for something a little more sano looking, you can buy the resistor wire for a 70s (and I think 80s) model GM. The circuit is supposed to supply 12v to the coil during startup (hotter spark for easier start) and drop to approximately 7.5V (I guessing on that on voltage) during normal run.

There is also an alternative option. There are after market coils out there for this conversion. It has a built in resistor, so you just hook up 12V to the coil and go. I have one of these on my truck right now and I hate it. My truck takes forever to start and it tends to cut out at high RPMS. I'm going to get rid of it soon, which leads me to my question.

It's been 15 years since I did this conversion and the guy that helped me do it died, so I'm trying to remember exactly how this circuit works. Here's the deal if I run a wire from the run position on my ignition switch through the resistor to the + side of the coil, I have power for running and starting but it will be about 7.5V. This is basically the same as the after market coil, but it moves the resistor to the outside of the coil. If I run a second wire from the starter solenoid contact on the ignition switch to the + side of the coil, I will have 12V at the coil only for starting then it will drop to 7.5 for run. My problem is that once released from the start position on the ignition switch it seems to the power would now flow through the resistor to the coil, back through the bypass wire to the start side of the ignition switch and then down to the starter solenoid. By the time it gets to the solenoid it has dropped to 7.5V so maybe this isn't enough voltage to energize the relay but it is enough to have me worried.

So what's the story? Do I have the circuit wrong or is the voltage too low to cause a problem.

Ronald L. Cook wrote: Rick--Your source of 12volts to the coil for starting needs to come from the starter relay at a separate post from the post your starter motor gets it's 12volts. When the relay is open so the starter motor no longer gets current, the post for the ignition current should also be open. All you need is the proper starter relay and do not wire the unresisted source to the starter switch but to the relay. Does this sound right to everyone?

James Roney wrote: STOP! You've got the circuit wrong! Your intuition is exactly correct, and if you do what you've proposed, you have created a circuit that will keep the starter engaged forever. Please be careful.

The ignition bypass circuit must be energized by a relay. Older GM style starters had this relay in the starter solenoid, while Ford used a separate relay mounted near the battery. If your starter has two small terminals, (and I'm pretty sure it doesn't) one of them will energize the solenoid, and the other will become hot (+12) when cranking. When the starter is not cranking, that terminal does not connect to anything inside the solenoid. When properly wired, you will see about 7.5 V backfeeding down the bypass wire.

Nearly all coils from the big three in the 60's and 70's are 8 volt (7.5) because the available voltage at cranking is 8 volts. It's like designing for the worst case. After cranking, the available voltage goes up to 13-14 when charging. In order to accommodate all available voltages, the coil is "dumbed-down" to 8 volts. This is why it has the bypass circuit. Even when it is working correctly, you should never measure 12 Volts at the coil.

I would be more than happy to provide you with the proper bypass schematic, but if I were you, I'd listen really carefully to that guy with the Chevette HEI distributor. It's a one wire deal, and those HEI's are bullet-proof. I'll bet that the advance curve is just about right too. It's probably worth $100.00 just to try it.

Rick Stivers wrote: Thanks James an Ron, I knew I could count on you guys to set me straight. James my budget at the moment doesn't allow for the HEI at this time although, it is in my future plans. Do they make a small head HEI for a 350 distributor. The only ones I've ever seen were too big to fit into my application without cutting out the firewall. I think for this type of application Fords are much better.

Anyway if I understand what you are saying, I need a relay installed to activate the coil bypass. That way when the starter circuit is deactivated the voltage cannot back-feed. Could this be done with a diode in the bypass line instead?

Ronald L. Cook wrote: Rick--I forgot you are Chevy powered. If you have the right vintage solenoid on your starter, there is a pole right there waiting for your wire.

Steven Dunlop wrote: The exact ohm value doesn't really matter, around 1-4 ohms should work OK. In addition to preventing the points from burning up, a ballast resistor will keep the coil from exploding if the ignition is left on with the engine not turning.

Carquest part numbers RU-10 and RU-11 seem to work OK. One of them is a temperature sensitive resistor that increases resistance as it heats up. The idea is that you don't need a starter bypass that way.

Even with a standard, fixed-resistance ballast a starter bypass is not strictly necessary, especially with a strong battery and clean ground connections.

The same parts can be used with moderate-current accessories, horn, heater fan, and the like. You have to do some experimenting to get the right resistance, sometimes using two or more ballast resistors in series or parallel.

Tim Lankins wrote: I use a universal coil on my 12V conversion with no problem .Paid $35 for it and no regrets.

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Rick Stivers wrote: Marshall, If the ballast resistor is installed properly between only the ignition switch and the coil then it should not cause a problem with your temp gauge. If on the other hand your temp gauge is connected to the + side of the coil (I really don't know why) then you could have this problem.

Trace the wiring from the temp sensor back to and through the gauge then back to source power. Let us know how it's wired and what else is wired in with it. It sounds like bad connections or a faulty sending unit, but until you've traced it you won't know for sure.

Bill Lagler wrote: Check the voltage level to the gauge with a voltmeter, probably easier than tracing wires.

Marshall Rimland wrote: Thank you one and all for your help. I'll get back to you and let you know what I find, as soon as I get the opportunity to play in the garage. Meanwhile it's running and starting like new.

If a coil has built in resistor, how does it get the full 12V for starting and 7V for running? Is there an extra winding and terminal in the coil?

Doug Traylor wrote: I have a large collection of auto manuals going back to

about 1932, if ya need info, let me know, but I might be slow answering you,

forty teens working on projects and forty plus years of working on

vehicles/instructing has slowed me down a bit and the arthritis does not



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David H. Hatch wrote: Guys, I am wiring a new/used Ford Alternator and external voltage regulator into my Jeep. Similar to what was already in there, but new stuff. The former sys was a FoMoCo alternator [not charging] with a GM/AMC regulator. With the new FoMoCo voltage regulator and used alternator, I am confused [normal for me] on the wiring. This is simple... for someone. My generator was gone long ago. Pls keep answer simple. Thanks.

My question: I am using an ammeter. Can someone tell me what wire goes where?

Jerry Adams wrote: OK Dave, here we go.

Dave Hatch wrote: EXT VOLTAGE REGULATOR has the following harness tabs:

F - This is connected to the "Field" terminal on the Alternator

I - This is connected to one side of the resistor on the firewall. - see below...

A - This is connected to the "Battery" terminal on the alternator.

S - This is connected to the "Stator" terminal on the alternator.

Jerry Adams wrote: All of the above wires carry relatively little current. A #14 wire (check the package at the parts store) will be plenty heavy for these wires.

Dave Hatch wrote: ALTERNATOR has the following tabs:

Stator - This is connected to the "S" terminal on the voltage regulator.

Field - This is connected to the "F" terminal on the voltage regulator.

Battery - * see below

Ground - There should be a #14 wire from this connection to one of the mounting screws on the base of the voltage regulator.

Jerry Adams wrote: You will need to make the following connections in addition to the above. The wires may already be in place, but you should check them to make sure the insulation is good and the connections are clean and tight:

From the other side of the resistor on the fire wall: Run a #14 gage wire to the "accessory" terminal on your ignition switch. If your switch does not have an "accessory" terminal, use the one running to the ignition coil. Do not connect to the terminal on the ignition switch that runs to the battery. You will drain your battery when the motor is not running if you do!

The AMMETER is simple to hook up, and most of the wiring may already be in place. Here's the way to hook it up:

I assume that you have the standard type of alternator that will put out about 60 amps maximum, and that you have only the average vehicle loads (lights, a radio, etc.) If you have a winch, you will probably benefit from heavier wire. Post here if you do, and I'll try to help. For a standard vehicle setup, you will need to wire your ammeter this way:

You should use at least a number 10 wire (again check the package) for all the connections leading to the ammeter. There will be two terminals on the back of the gage. They may or may not have any markings on them. You cannot damage the meter if you happen to get the connections reversed, so that is not a problem.

You should run a heavy (#10) wire from one side of the ammeter to the positive post on your battery. Most of the time, this is done by running the wire to the terminal on the starter solenoid that has the battery connected to it. Note that this wire will cause some considerable fireworks if it comes into contact with any part of the body, so make sure that it is well insulated where it runs through any holes. I like to use a short piece of vacuum hose for protection where ever any wire passed through a hole. This should be the only wire connected to this post on the ammeter.

There should be two wires connected to the other post on the ammeter. One will run directly to the "Battery" terminal on the alternator. This should be at least a #10 wire.

There should be another wire connected to the same post on the ammeter as the wire running to the alternator. This wire is used to provide power for the lights and ignition switch. A #12 wire will do, but if you have enough #10 on hand, you might as well use it. The simplest way is to run a heavy (at least #12) wire from the ammeter to the "BAT" terminal on the ignition switch, then run another wire from the "BAT" terminal on the ignition switch to the "BAT" terminal on the headlight switch. Most headlight switches have a circuit breaker mounted on them that has the "BAT" terminal on it. You can run a #14 wire from the other side of the circuit breaker to the break light switch, and the turning signals if you have them.

The horn relay usually does not connect to the ammeter, but is instead connected to the battery.

After you get everything hooked up, turn on the headlights. The ammeter should swing to the "D" or "DISCHARGE" side. If it does not, simply reverse the wires on the ammeter to make it swing the other way. I hope this helps.. E-mail me or post here if you have any further questions.

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Solsidan wrote: Is it logical, safe, possible to use the 6 volt setting on a battery charger hooked up to the battery cables to turn an engine over to check the compression. I've got a battery on the way but want to get going. A check with a multimeter looked like it was putting out about 9-10 volts? Is that likely?

Chuck Pedretti wrote: It would probably burn out your charger or just not turn the engine unless your charger has a boost start setting, even then the battery is needed to smooth out the voltage, it acts like a regulator for the battery booster.

Jerry Stoper wrote: Unless its a very powerful charger, you won't get enough amps to turn the engine over and will probably burn your charger out.

Richard Grover wrote: I agree that most chargers do not have the amps to turn the engine, but most chargers do have breakers, so it probably wouldn't hurt to try. If your charger has a high amp setting, it might do it. Most chargers, like my $30 Excide, only put out a few amps. I don't know how many for sure (maybe 10), but not 500 or more you'll want to spin the engine.

Ben Page wrote: Got a crank handle?

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David Page wrote: Richard, does this mean that I can jump start my 6 volt system with a 12 volt system? What precautions should I take?

Richard Needham wrote: David If you jump start a 6v system with a 12v battery, you run the chance of burning out your voltage regulator and generator also 12v could be to much for your 6v coil and could ruin it I wouldn't advise it.

Rick Stivers wrote: Not to mention the fact that hooking a 12 battery to a 6 VDC system would be about the same as hooking up a constant 6 VDC drop across the 12V battery and would probably melt it down or blow it up. But this is Jerry Adam's forte. So Jerry, how disastrous would this be?

Chuck Pedretti wrote: If you're going to jump a 6 volt system with a 12 volt vehicle, leave it turned off. I do this all the time with a riding lawn mower, most of the 6 volt stuff isn't very sensitive to over voltage, in fact I think that a 6 volt system is generally running at about 9 volts while running (same way a 12 V system runs at 13.8).

Glenn Goodman wrote: Here we go again. Hope everyone can read this. (I'm the one that keeps sending hieroglyphics.) I've jumped 6v with 12v more than once. You want to move fast, and yes, leave the 12v vehicle OFF. Two people are best. One to be the starter and the other is ready with the negative connection. When the first person is ready to start the second person attaches the negative side to a good ground (not the negative battery terminal) and as soon as the 6v vehicle is started the second person unhooks the ground. Works pretty good.

John Okuley wrote: Although I felt a similar worry, I have used a running 12v car to start a 6v system with no apparent damage to either electrical system. My "bubba" mechanic friend, who I trust, said to just hook up the jumper cables like you normally do, with the 12v car running. Then we cranked the 6v system. It will crank faster, because with (12v+6v/2) you are now running a 9v battery, or so I'm told. I no nothing about long term damage to the coil, points or condenser, but bubba said for the short term it wouldn't hurt a thing. A lot of old farm tractors are 6v, and they often get jump started by 12v pickups. If my mechanic had gotten frustrated after too many Rolling Rocks, then all bets are off. Your mileage may vary.

Richard Needham wrote: Guess I stand corrected. Learning something new everyday.

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Sean R. Kerns wrote: Hi, I have a '48 CJ-2A with the L-134 that has been converted (mostly) from 6 to 12 volt. One thing I forgot about is points and condenser. Can anyone who's done the conversion recommend a part number or year and model to ask for to get a 12V set of points and condenser that'll work in the stock distributor? I'm sure NAPA has it, but getting those guys to look it up is hit and miss, to say the least...

Rick Stivers wrote: Sean, The original points and condenser work perfect for the 12V conversion. Unless you are using a 12V coil with a built resistor, you need to install a ballast resistor so that you don't burn out the points.

Sean wrote: I hope I didn't hurt anything in the couple of minutes it was running.

Rick Stivers wrote: Sean, I ran my 52 chevy for all most 3 weeks before I welded the points so bad it wouldn't run. You should be fine.

Sean R. Kerns wrote: Thanks, Rick! That's the other thing I have to check out. I don't remember whether the coil I got has an internal resistor or not. After I did the conversion, I started the Jeep up for a few minutes, just to see if it ran, and I haven't run it since, because it's waiting till I have money to put an exhaust on it. I hope I didn't hurt anything in the couple of minutes it was running.

Tim Lankins wrote: I did my 12v conversion in July and used a twelve volt universal coil but no ballast resistor . Am I on borrowed time on my points ? and will the local parts house know what I mean when I ask for one ?

Donald Tarczy wrote: You should be able to keep the current 6V points and condenser but you should put a ballast resister in the run circuit and bypass the resister for starting. As far as I know all 12V vehicles run on 6V and start on 12V. Chrysler vehicles had a ceramic resister mounted on the firewall for this purpose and think they only cost a few bucks, but I would buy a spare because they did have a habit of burning out from time to time

Arne Anderson wrote: I have done many a tune up on my L-head and found that my local parts guy always got me the right parts without me ever specifying 12volt or 6volt probably because they don't listn 6 volt points or at least the guy I go through doesn't seem to list them oh well I hope this helps.

Rick Stivers wrote: Tim, If the coil you bought uses an internal resistor it will probably say so on the side of it. If it doesn't say so, it probably isn't. As for borrowed time? If you are running a standard coil without the resistor, the points are probably arching pretty bad. If your condenser is really good and your points were top of the line, then they may last a while before going out.

If the points do burn up on you, just file them and readjust them, so you can get home. As for buying a ballast resistor? A lot of people buy them to fit 60s and 70s Chryslers. They are pretty tough and easy to install but they are also pretty ugly and they get very hot. Install them where they can get plenty of cooling air and away from things that can be heat damaged. Other people prefer to just buy the coil with the built in resistor and these work fine if you have a good strong battery. The only problem with these, is that they won't have as strong a spark when cold cranking your engine. If you do need to install one let us know and I think we can set you up with the wiring info.

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Jerry Stevens wrote: Chris & Lise, Try They have a device in their line of stuff "precision regulator", that may solve your problems.

Mike Mock wrote: Hi Chris, I'm in the same bucket for the 6 to 12 volt conversion. The guys here cued me into . They suggest a small voltage regulator, pn 7806 that does 1 amp, and goes for about $1.50 from most electronics stores. There was also a great deal of information for me in Rick's revision of FAQ's for pickup trucks. goes through the install of an alternator. has some more stuff. Good luck

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Ron Smith wrote:  I was driving around in one of my Willys with a friend of mine when he mentioned that I really didn't own the Willys. Rather, I was more like a caretaker for it, as sooner or later I would pass on ownership to someone else (I'm picturing here my dead hands being pried off a steering wheel).

He has a good point. Most of our Willys will be owned by someone else sooner or later, possibly by others on this list. With that in mind, I would like to post the following for the current owner of the next Willys that I will own (the rest of you can ignore this):

Dear POSAPO (Present Owner, Someday A "Previous Owner"):

1) After you crimp a wiring connector onto a wire, give the wire three strong tugs to see if it comes loose from the connector. Don't be timid here – a good connection can with stand a good tug. (Every single wire on the Willys that I am currently re-rebuilding pops free of its connector with a light tug or sometimes just a stern look...)

2) Don't go out and buy 500' of red wire and then use it for everything. They do make wires in different colors and it doesn't cost much more to use them. Trouble shooting is a whole lot easier if you are not try to trace 1 red wire out of a nest of 23 red wires.

3) A wire that starts out one color should be more or less the same color at the other end. (True, the few non-red wires are a pleasant novelty, but a wire that starts out green, then turns blue, then goes yellow... you need to keep in mind that someday we may meet again!)

4) If you are rewiring the car and you have a large bundle of wires going from Point A to Point B, why not throw in 2 or 3 extra wires while you are at it. They don't cost much and they can save messy rework later when I finally figure how to fix the hash you are currently making of the wiring (and please label them as spares at each end, too! Jeepers, do I have to tell you everything!).

5) Do not use non-UV resistant tie-wraps (they are usually white, but sometimes black also). Use tie-wraps that are clearly labeled as "UV resistant" (almost always black in color). The whitetie-wraps on my current project will crumble with a slight tug (like when I am testing the #$%&@ crimped connectors…).

6) Sketch out what you are going to do before you do it. Grab a napkin or a shopping bag or something and do a wiring diagram. Make up your own symbols or whatever, but at least have a plan before you run wires (My current project has a 10 gauge wire (red, of course) running from the alternator to over near the amp meter but not quite to it, then back to the battery, and then back to the amp meter, with 6 splices in it (all red wires) (all coming loose) going Lord knows where...) Greed Note: I will be glad to pay you extra money for your vehicle if you are able to include the napkin or shopping bag with the deal (assuming the document has some vague acquaintance with reality).

OK, enough for now. Maybe more later – right now I've got togo stick some more pins in the PO voodoo doll that I made. Maybe I will park a tire on top of it...

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Why not to run 6 volt motors from a 12v source

Dinarte Santos wrote: Ohm's law is V=IR

Where V is Voltage (Volts)

I is Current (Amps)

and R is Resitance (Ohms).... and applies to a linear resistor, which is by definition one that complies with Ohmīs law...

A DC motor, however, is not a linear resistor, but consists of a resistor (winding resistance) in series with an inductor, formed by the copper wire wound around a magnetic core. Also in series with the resistor and the inductor is a voltage generator, which generates a voltage proportional to the electric motorīs rpm.

By the way, the torque felt by the fan shaft is proportional to the current flowing through the motor windings, thatīs the way the electric motor converts energy from electrical to mechanical and vice-versa.

The torque needed to turn the fan shaft is proportional to the square of its rpm, hence now we have a non-linear element in the circuit. The power needed to turn the fan shaft, being proportional to the product of its rpm by its shaft torque, is then proportional to the 3rd power of its rpm, hence to turn a fan shaft at twice the designed speed, itīs necessary to apply 8 times more power...

To say that the fan shaft torque is proportional to the square of fan shaft speed is the same as saying that the fan shaft speed is proportional to the square root of the fan shaft torque, thus a DC model of the electric motor + driven fan assembly can be drawn and simulated. The effects of the windingīs inductance and rotorīs inertia donīt have to be considered in this model, as they would have to be in a dynamic model. Such a model would look like this:

dc_electric_motor_graphics.gif (9391 bytes) dc_electric_motor_model_2.gif (18504 bytes)

(dc electric motor model, attachment) and the resulting graphs as the driving voltage is increased from zero to twice its operating ratings are: (dc electric motor graphs, attachment) motor rpm, green trace motor current, red trace power drawn from the battery, blue trace power dissipated in the motor windings due to Joule effect, yellow trace

As can be seen from the graphs, both the power drawn from the battery and the power dissipated in the motor windings increase rapidly as the voltage applied to the motor terminals is increased above its nominal operating voltage, leading to motor overheating and winding insulation failure, followed by a short circuit and clouds of smoke...

To avoid this, the motor could be rewound to 12V, or else a step-down converter could be used. Connecting a resistance in series with the motor would also work, but now the resistance would dissipate the same amount of power the motor itself would draw from a 6V battery, hence it would be wiser to use a switching mode converter, thatīs basically a high frequency oscillator that turns the power on and off to the motor at a frequency high enough to allow its windingsī inductance to keep the current flowing through them almost constant - thus the motor windings would "feel" a 6V battery instead of a 12V one, and there would be no power dissipated in external resistors.

Dr.Vern wrote: Dear Friends, I read Dinarte's most excellent post about electric motors and voltage changes.

I'm not worthy! I'm not worthy!

I locked myself in the basement for a ControlledScientificExperiment(tm) with a 6v-heater motor. I thought it would be fun, and hopefully somebody else does too, to see exactly how much amperage a 6v-heater fan would draw. Then let's see what would happen on 12-volts. But please note I am not going to run the 6-volt motor on 12-volts. I am merely going to extrapolate the results on 6-volts.

My crusty old cobweb-filled motor pulled 7 amps at 6-volts. A freshly serviced motor might draw less, but then again the dirty brushes on this one may be limiting the current. I think the 7 amps is a reasonable number for guesstimating purposes.

Power consumption, or wattage, is voltage x current. So my old fan motor was consuming 42 watts of energy. Like Dinarte said, figuring the resistance of a motor is a complicated thing due to inductive reactions from the coils. I used to understand all that stuff but have forgotten most of it because it is rarely needed.

For simplicity, let's assume (Danger! Danger!) our fan motor is a giant resistive load with no inductive reaction. By using the formula of Voltage = Amperage x Resistance, we determine the fan motor has a resistance of 0.857 ohms under load.

If we double the voltage to 12, the amperage will jump to 14 amps. (12-volts = 14 amps x 0.857 ohms, which is a more or less constant) Looking at power consumption, it had increased exponentially to 168 watts! (12-volts x 14 amps) That is a lot of power being consumed by our lowly 6-volt fan motor which is designed to handle a meager 42 watts or so. You could maybe do it on an intermittant basis, which is how a starter is designed, but not for a continuous duty application like a heater fan. Running the heater fan for only a few seconds at a time would get old. <g>

Well then, what about the premise that on 12-volts, a system draws half the amperage compared to 6-volts? That is only true with components designed for 12-volts, not when you run 6-volt stuff at 12-volts. For any 12-volt component to produce the same amount of work as our fan motor on 6-volts, it would have to be designed with a higher internal resistance. By working the formulas backwards, a 12-volt fan motor with the same 42 watt consumption (and same power output if the efficiency is the same) would have a resistance of 3.43 ohms, instead of the .86 ohms of the 6-volt motor. The 12-volt motor would draw only 3.5 amps, which is indeed half of the 6-volt motor of the same output. (3.43 ohms x 3.5 amps = 12-volts. 3.5 amps x 12-volts = 42 watts)

Oh well, it has been a while since I've had any reason to play with these formulas. If you get lost, don't despair. In a continuous duty application, which is pretty much everything but the starter, only runs at the design voltage. Like I got to rambling about yesterday, the 6v-starter motor can safely run at 12-volt with certain precautions. But most any 6-volt motor runs continuously on 12-volts will run very hot and very fast. It can get hot enough to melt the solder connections. It can run fast enough to birdcage the armature windings. Brush life will be very short, as very high amperage will be present across the brush to commutator contact points. The commutator surface will probably get severely pitted, too.

Now that you have me started, let's talk about how to get 6-volts for the motor from a 12-volt system. Actually, like others have said, swapping in a 12-volt fan motor is probably the all-around best solution. Most of the fan motors are pretty universal and this can be done easily with the right parts.

But let's say your only option is to keep your 6-volt motor in a 12-volt system. Rick's story about smoking the dropping resistors shows an important aspect about the subject. If you wire a resistor in series like that, it must dissipate the same energy as the fan motor. In our 6-volt fan motor example, that is 42 watts that must be dissipated by a giant dropping resistor. That is a lot of heat.

In addition to the heat problem, dropping resistors are not a very good solution for most applications because of another factor. A dropping resistor must be matched exactly to the load to work properly. It would be like hooking a pair of 6-volt bulbs in series to work on 12-volts. As long as both bulbs are identical, they will each get 6-volts. The same thing is going on with a dropping resistor. The resistor gets 6-volts, and the fan motor (or whatever load) gets 6-volts. But should anything change, like wear in the brushes or the shaft binding, the voltage across the motor could change dramatically. Depending on the circumstances, the motor's new voltage could drop near zero or soar near 12-volts. Imagine if you tried to use a dropping resistor with a multi-speed fan. I don't know if it could be done, as the fan's total resistance would change depending on the switch setting.

If you are using a dropping resistor on a small, constant load, you could get away with it. On a low amperage circuit, the dropping resistor wouldn't have to dissipate much total wattage. But very few circuits have a constant load. A fuel gauge, for example, draws varying current as the sender changes. On any type of lighting circuit, which are relatively constant, you'd just change the bulbs. Even a radio draws increased current as you increase the volume. I can hardly think of any applications where a dropping resistor would be effective.

This is where the transistorized voltage regulator or reducer shines. I don't mean the type that controls the alternator on newer cars. What I am talking about is one of the little gizmos that takes 12-volt input and provides 6-volt output. The beauty of these is that the output voltage is not dependant on the load in the output circuit. If the output circuit draws 1 amp, it stays at 6-volts. If it changes to 15 amps, it still stays at 6-volts. Now if you tried that with a dropping resistor, the voltage would be all over the place.

I will readily admit I have no idea what goes on inside one of these little gizmos. Nor do I really need to know. All I need to know is that with a 12-volt input, it will have a steady 6-volt output circuit. You can buy these voltage regulator devices at most auto parts stores. I see them advertised every month in Hemmings. I think the J.C.Whitney item previously shown is one of them.

If you think about it, the Instrument Voltage Regulator (IVR) on the back of the later model instrument cluster does the exact same thing. It takes an input (6 or 12-volts, depending on the year) and produces a nice even 5-volts for the instruments. The IVR is a mechanical device, but its end result is just like the transistorized unit for 12-volt conversions that we have been talking about.

When choosing a voltage regulator to keep 6-volt accessories on a 12-volt conversion, just make sure it has sufficient amperage capacity. Some are light duty, with only a few amps available to run instruments, etc. There are heavier duty versions available with enough capacity to run a heater fan. I think the J.C.Whitney item previously mentioned is sufficient to run a fan motor, but I'd have to read all the fine print to be sure. You could also use more than one if needed, i.e. one for the fan, another for the instruments, etc...

Well, I hope you have enjoyed this little RambleFest. I kinda got carried away. I hope this makes sense and that this helps in some way...

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This page last updated 22 October, 2000 [Hit Counter]