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Grease Monkey
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Grease Monkey
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I thought I run this pass the experts out there. I know there must be someone who has done this so any advice will be welcome. I am going to keep my 1933 sedan on 6 volts but change out the generator for an alternator. The only alternator that looks like the stock generator I have found is a 60 amp. My amp gauge is only a 20 amp’. Will the 60-amp alternator destroy the stock gauge? Or will I need to bypass it? I was thinking of just running a wire straight to the battery as well as the stock wiring going throw the 20-amp gauge with a 2000-ohm resistor before the gauge for show. If my math is right and that’s a big if, the gauge should read a 1/3 of what the Alternator putting out. The regulator should take care of any overcharging.


Buggy work's
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Oil Can Mechanic
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Short answer: Yes, it will burn up the gauge, but probably wont happen immediately. It will happen at random some day when the battery is low, the day the battery draws quite a bit more than 20 amps. The easy answer is bypass it.

The longer answer is it is possible to add a shunt. One would crimp *and* solder some *very short* wires to ring terminals. Use different gauge bare wires, but all the same exact length. Bolt on the back of the ammeter to short the terminals together. Keep going smaller until you have the full scale reading you want.

I would start with something huge, like maybe #10. You would need an adjustable battery load tester, and need to rev the engine up enough that the alternator is capable of full current. Add load to the battery. Be careful. Don't peg the ammeter and burn it out.

When everything the alternator can do gets you *almost* full scale, you are there.

Note, your charging circuit wiring likely needs to be bigger for 60 amps. If it is too small it will get HOT.

(That would be the wires from the alternator to the ammeter, and the ammeter to the battery.)

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I don't know of any mathematical equation that would involve a 2000 ohm resistor in your setup. Most folks bypass the meter and install a voltmeter somewhere. Some actually take the original meter face and mount a voltmeter movement behind it. In that case you have to know where the needle points when the voltage is correct.


My 1951 1 Ton is now on the road! My 38 Master 4 Door is also now on the road .
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If you want the gauge to do anything close to original, you will need to shunt it with a parallel path like Bloo said. You could use wires or do some math and add a wirewound resistor for a shunt.
If you wire a resistor in series as your post suggests, the gauge effectively becomes a fuse as it is still a weak link in the circuit. At some point it will let you down.

I'd be tempted to do as old216 said and add voltmeter guts or find an ammeter rated more than the new alternator and use those guts in your stock gauge.



1938 Canadian Pontiac Business Coupe (aka a 1938 Chevy Coupe with Pontiac shaped front sheet metal - almost all Chevy!)
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Oil Can Mechanic
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A 2000 ohm resistor wont help. Ammeters measure flow. The system wont get to 60 amps until something on the far side of the ammeter DRAWS 60 amps. Generally that means the battery.

Since the system is capable of supplying 60 amps, the ammeter needs to be capable of handling that flow.

Ammeters are a dead short internally. There will already be a shunt inside. You will need to add another, in parallel. It will be WAY less than one ohm. It would be a short wire running directly between the posts. It will be carrying 40 amps when the ammeter is carrying 20. This will be a BIG wire. #10 was a wild guess. It will have to be determined experimentally.

It could get hot at high current. It probably needs to be bare, with things tied away from it just in case. Plastic insulation could burn and stink. I might put some (fiberglass?) "motor winding" sleeve (from an electric motor rebuild shop) around it. An appliance repair outfit might also have heat-resistant sleeve material.

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Grease Monkey
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Grease Monkey
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Thank you Thank you Thank you ALL
The add a shunt thing is a very good Idea, Why did I not think of that. I have the stickers to make up a newer gauge as well, I was looking @ that as well. I think that maybe the safest way to do this if I can find a gauge with a pointer that looks like the stock one in my car. I think the older SW's do. Keeping this car looking as she did back in its day is most important to me. But making it reliable is to. Driving with the lights and radio on is a lot of drain on 20-amps, that is if you can keep her revved up to 2K @ stop lights I drive her all the time as long as its day time. Now I be able to drive her @ night as well. I am so happy to be part of this forum you folks are a lot of help.


Buggy work's
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This doesn't answer any of your questions.

I'm just wondering why in the would you go to all the trouble to install an alternator when a properly functioning generator will work just fine and adoquate? What is to be gained with the switch?

Boggles my mind. hood

Best though,

Charlie computer

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The alternator charges a little at idle speed and a generator does not.
In my many thousands of miles in driving cars with a generator I never had a problem.
Where the alternator would be an advanage is if you drive at night with the lghts on in heavy traffic and engine is at idle speed for long peiods of time.
A pre voltage regulator car with a 12 amp generator is another story.

Last edited by Chev Nut; 07/27/20 07:53 AM.

Gene Schneider
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This article explains how to improve your original generator:

https://www.ply33.com/Repair/lights

Here's the key, hiding an actual voltage regulator inside the original generator.

https://www.ply33.com/Repair/voltreg

This actually works, even with halogen headlight bulbs on my '36 Chevy PU, contrary to assertions by various "Experts" that 1930s era generators can't power halogen bulbs.

Ray W

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I have been running a Peterson regulator for about 15 years (can't remember actual start as it has been too long). It is installed on a '31 Chevrolet three brush generator (Delco-Remy 643J). Other than the initial installation (first one on a Chevy generator) it has been trouble free. I routinely move it to other Chevys when I take them on tours and outings. As Ray W. wrote "It actually works, with ...... headlights" has been my experience as well.

The best part is it dramatically reduces the water loss and increases the battery life compared with the stock generator only.


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"The best part is it dramatically reduces the water loss and increases the battery life compared with the stock generator only."

Thanks for chiming in Chipper. To me the other "best part" is that it reverses the absurd tendency of the three brush generators to make less power as they speed up. With the regulator, electric output is not diminished with increased speed as it is with the original setup. That is welcome because we need brighter lights as we go faster, not dimmer lights.

Being a hard core do-it-yourselfer you will laugh at how I got mine. A guy on the 1936 Chevy Owners forum bought it and had it installed by a PROFESSIONAL AUTO ELECTRIC SHOP. The problem was that once installed it didn't work and the "Professional" who installed blamed the unit, calling it "defective". So in disgust the unhappy owner gave me the whole generator for the cost of shipping it.

I contacted James Peterson and got the installation instructions and the problem was obvious immediately. It was not installed correctly! In order to connect one of the wires the generator has to be disassembled to get access to the connection point and the "Professional" was too lazy to do that. In saying this to you I know I'm preaching to the choir but this is yet another example of the validity of the ancient saying "If you want something done right, do it yourself". As if to further make the point of the value of doing things one's self instead of paying "professionals" to do things wrong, the incorrect installation toasted the generator (burned off insulation and "thrown" solder) but the Peterson regulator survived because it was not fully wired in. So the toasted generator went into the trash and the Peterson regulator went into the generator on my '36.

The thing has been in for years now and my amp meter shows a big charge when the engine first starts because the '36 is only driven every couple of weeks and the charge diminishes to a trickle once the battery is recharged. Pretty cool for a completely hidden "stealth modification", huh? And with halogen headlights I can actually see the road at night. That matters on the dark country roads where I live where the closest street light is about 10 miles away.

Ray W

Last edited by brino; 07/28/20 06:48 PM.

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