Reproduction Parts for 1916-1964 Chevrolet Passenger Cars & 1918-1987 Chevrolet & GMC Trucks


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I am self taught and most of my knowledge comes from the late 1980's era GM 4.3 v6 with TBI. I know this is a different animal but that is what is in the car that got me into this hobby. Now I am working on a 41 Master Deluxe with the original 6v system.

My charging system knowledge was that the alternator at all times supplied enough power to run the engine and car's electronics. Any excess was used to charge the battery. The output of the alternator should should be enough to do this plus a percentage incase added draw is required at any time.

Now I thought a generator was just a did the same thing but with a different technology. I thought all the same rules applied, then I asked a question in another thread and received an answer that made me realize how wrong I may be.

Rusty 37 stated, 'Remember that a generator provides no output at idle.'

Now I have the following questions:
1. At idle is the generator or the battery providing the power to run the engine. I.E where is the power to the coil coming from?
2. Will the car drain the battery if left to run at idle for an extended period of time?
3. Does the battery only charge while driving?
4. What is the difference between 40 amp at 6 volt and 40 amp at 12 volt? I was just adding up the amount drawn by each item at once and making sure it was less than 40.
5. How many amps are used by the engine?
6. How many amps are required to maintain the battery?
7. The amp meter appears to work, I only watched the gauge while idling the car. I noticed it was on the charging side and thought nothing of it being steady. Is this how it should be?
8. I keep the car on a 6v trickle charger with a battery disconnect disconnecting the car from the battery at all times other than when working on it. Is this the best practice? It is one of the quick connects with a dial to connect the battery. I use the same one for storing my Monte Carlo in the winter.

I am currently in the stage of wiring everything. I am using copper wire (not copper clad) and replacing with the same awg or larger. I was under the impression that a 6 volt system would require a larger wires than a 12 volt system. Is this correct? All the wiring in the car was larger than that in my current one so I thought it must be correct.

Sorry for the long post. I and my kids are learning as we go. We knew we were up for a challenge getting into this. Unfortunately we seem to spend 50% of the time on the planning, 20% finding parts, 20% working, and 10% wasting time wondering what we just did.


I have found that having an old car is a constant project that is never done. I think that is a good thing. Keeps me learning new things. Having two from different eras is just a form of higher education.
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I can't answer your questions but if you are duplicating the original wiring and have a, properly functioning, charging system, You should have no problems.
The generator requires a few revs above idle to produce current. I suppose that means that, if left to run at idle for several hours (days?), the battery would run down. I have been driving 6 volt Chevys for 60 years and have never given this any thought.
I think your battery disconnect is a good idea. Keep doing what you are doing, let common sense be your guide, keep your Boys involved.
You are doing something that is important on many levels. My Son is 42 now, and lives 15 hours drive time from me. He is my favorite "Old Car Buddy", whether wrenching, swap meet-ing, or just planning and B.S.-ing.

Mike


ml.russell1936@gmail.com

Many miles of happy motoring
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Hi Mr87Monty

I've heard it said many times that a generator won't charge at idle.
All of my generators DO charge at idle speed. If your ammeter needle is centered when not running, and is to the right of center when idling as you said, yours is charging at idle also.

So... with the engine running but all other electrical items off:
If the ammeter is reading a charge at idle, the current to run the engine is coming from the generator.
If the ammeter is centered at idle, the current to run the engine IS STILL coming from the generator.
If the ammeter is between centered and about 3-4 amps discharge, the generator is producing current but not enough to keep up with the needs of the engine and the battery is making up the difference and slowly discharging.
If the ammeter is showing more than about 5-6 amps discharge, the generator is NOT producing current and the battery is carrying the whole load and of course discharging.

Good batteries do discharge themselves VERY slowly over time.
So maintaining a full charge will require a small current over time as well.
That current is quite small and a trickle charger will supply more than enough.
So, what you are doing with your trickle charger is ideal.

You are correct that wiring in a 6 volt system will be heavier than in a 12 volt system.
This is of course due to the fact that to deliver the same wattage (power) to a fan motor for example, you need twice the amperage at 6 volts compared to 12 volts.
And of course wire size requirement depends on AMPERAGE, not voltage.

And to close...
Forty amps at 6 volts will deliver 1/2 the wattage/power that 40 amps at 12 volts will.
Probably the reason the switch was made to 12 volts.
But on our old vehicles with limited bells and whistles, 6 volts does the job just fine.

Hope this helps! :-)


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If Everything is correct. There is no charge at idle speed because the generator is not producing enough and the points in the cut out open and the ammeter will show discharge, the amount depending on what electrical devices are on, which includes the ignition.
The advantage of an alternator was it does charge at idle (but not the full amount of amps) to prevent draing the battery if there is a lot of draw from lights and eletrical accessories.

The points in the cut out also open when the engine is not running, if they did not the generator will draw the charge out of the battery.

Yes, if you would let the engine idle for an extended amoumt of time with lights on with a generator it will drain the battery.

Last edited by Chev Nut; 02/18/22 01:52 PM.
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Great questions and you are getting good guidance in the responses. The ammeter tells you if the generator is providing the current to run things (+ side) or the battery is the source (- side). Eventually the battery will discharge itself if the needle stays to the - side after running for extended periods of time. Ole’s statement about battery discharge over time is the reason many of us use maintainers on our batteries. I even have one for my wife’s lawn tractor so I know it will be ready to go in the spring.

The generator on my ‘37 is a slightly different design and less than half the output of yours. So my experiences are not quite the same as what you should observe. I also had both a 1950 and a 1953 Chevy as my first 2 cars.

In all those vehicles the ammeter did indicate a discharge at idle when the headlights were on. At idle with the lights off the ‘50 & ‘53 ammeters showed neutral to maybe slightly to the + side. In my ‘37 the ammeter always goes negative at idle. It’s the nature of that charging system. Plus I have a sealed beam headlight conversion on it. So at night the best I get is a neutral reading on the ammeter when driving. The generator just barely keeps up with the load from all the lights. If I have the fan motor on it shows negative.

It is very normal for the ammeter to show a high charge rate just after starting the car and then the charge rate tapers back to just above middle as the charge is restored in the battery.

It is easy to check how much load it takes to power the ignition on the engine. Just turn the key on, do not start the engine, and watch the ammeter. If the points are closed you should see the ammeter needle move slightly to the left. That is the current going through the coil. It is probably around 3 to 5 amps. If the points are open there should be no needle movement. Turn the key off and bump the starter to close the points. Then check again.

The real concern is if the ammeter shows discharge when the engine is running at higher speeds. If you turn on the headlights while driving down the road the ammeter needle will probably jump quickly to the left and immediately return to a little bit on the + side.

Ole is correct about the increased amps (double) required to provide the same power in a 6 volt system compared to 12 volts. As he stated, amperage defines wire size. Another way to think about it is the total watts (power) available in a system. A 6 volt generator with 40 amps of output provides 240 watts. 12 volts at 40 amps is 480 watts. I agree that is why automotive went to 12 volts. The wire sizes and generator get pretty big to support a 480 watt total load at 6 volts.

You might want to spend a little time researching the load capacity of the disconnect you are using. Most of the disconnects on the market today are designed to handle the amperage of a 12 volt system. On these old 6 volt cars many of us run at least 1/0 if not 2/0 cables for both the starter and the ground. The typical 12 volt start cable is probably 4 gauge or if you are lucky to find it 2 gauge cable. That size will probably give poor starter performance on 6 volts in your car in cold start or very hot conditions. The disconnect device could also be a limiting factor.


Rusty

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Originally Posted by Rusty 37 Master
You might want to spend a little time researching the load capacity of the disconnect you are using. Most of the disconnects on the market today are designed to handle the amperage of a 12 volt system. On these old 6 volt cars many of us run at least 1/0 if not 2/0 cables for both the starter and the ground. The typical 12 volt start cable is probably 4 gauge or if you are lucky to find it 2 gauge cable. That size will probably give poor starter performance on 6 volts in your car in cold start or very hot conditions. The disconnect device could also be a limiting factor.

The disconnect I am using is a coper block that claps to the battery terminal at one end and has a post at the other. There is a bolt in the middle that lifts the two parts apart when to break the connection. It is thinker than the cable going to the started so it should not be limiting anything.

Currently I am in the process of making all the harnesses to the lights so I can not test any of that for a bit. I do have the wires to the coil done. The other ones in the dash still need to be replaced. When I got the car the wires where cloth and several had lost their insolation. How it ran on the test drive without shorting out I have no idea.

Thanks for all the detailed answers. This is a learning experience all the help has been greatly appreciated.


I have found that having an old car is a constant project that is never done. I think that is a good thing. Keeps me learning new things. Having two from different eras is just a form of higher education.
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It sounds like you and your boys have lots of challenges theses days. I was faced with the exact same situation when I got my '37. Every time I touched a wire the insulation disintegrated. I went the "easy" route and bought a reproduction harness. it took me around10 hours over a couple of days to remove the old harness and install the new one.

I have that style disconnect on a "newer" 12 volt classic car. It works fine on that car with its 125 amp rating. There are similar disconnects that have slightly higher ratings, up to 200 amps I'm not sure that even the 200 amp switch would work on my '37. The no load draw on it is 125 amps. The starter on your '41 can draw over 500 amps if the rotor locks up. During normal starting it easily draws 300 amps.

The capacity limitation of that disconnect is based on the net area of contact between the 2 pieces. The bolt does not carry any current. As you noted, it simply makes or breaks the connection.


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Lots of good information in this thread so far.
Originally Posted by Mr87Monty
I am self taught and most of my knowledge comes from the late 1980's era GM 4.3 v6 with TBI. I know this is a different animal but that is what is in the car that got me into this hobby. Now I am working on a 41 Master Deluxe with the original 6v system.

My charging system knowledge was that the alternator at all times supplied enough power to run the engine and car's electronics. Any excess was used to charge the battery. The output of the alternator should should be enough to do this plus a percentage incase added draw is required at any time.
That is correct.
Originally Posted by Mr87Monty
Now I thought a generator was just a did the same thing but with a different technology. I thought all the same rules applied,
Yeah, pretty much.
Originally Posted by Mr87Monty
then I asked a question in another thread and received an answer that made me realize how wrong I may be. Rusty 37 stated, 'Remember that a generator provides no output at idle.'
He's right. It might provide no output at all, or it might provide a tiny bit. You sure wont get half the rated output like you would with an alternator. Assuming we are talking about your 41, or any of the large 2-brush generator systems with a 3 relay regulator that became common around 1940, it is 99% a non-issue. You will never know the difference unless you are some outlier that is commuting at night through a million stoplights in the rain with the lights and radio on and the defroster on high. Even in that case, your regulator could be turned up a tiny bit and you would probably still be fine.
Originally Posted by Mr87Monty
Now I have the following questions:
1. At idle is the generator or the battery providing the power to run the engine. I.E where is the power to the coil coming from?
Either or both. It all comes from the charging system as long as there is enough being generated. If the charging system cant keep up, then some comes from the battery and the overall voltage is lower.
Originally Posted by Mr87Monty
2. Will the car drain the battery if left to run at idle for an extended period of time?
If the radio or lights or something are on, then yes, definitely. With just the ignition probably not. Ignition doesn't draw much. Maybe 2 amps? maybe 4? If the generator is charging at all, and the cutout is pulled in, it would probably just carry it, or at least most of it. If the cutout is not pulled in, the battery would have to carry it. It would discharge according to it's amp/hour rating. I think you would run out of gas first, even if you had a full tank.
Originally Posted by Mr87Monty
3. Does the battery only charge while driving?
Yes, as described above. It might or might not charge at idle, but if it does, the amount will be negligible.
Originally Posted by Mr87Monty
4. What is the difference between 40 amp at 6 volt and 40 amp at 12 volt?
To do work, you need watts(power). Multiply volts(they're kind of like pressure) times amps (they're kind of like flow) to get watts. 40 amps at 6 volts can do the same amount of work as 20 amps at 12 volts. 40 amps at 12 volts can do twice as much.
Originally Posted by Mr87Monty
I was just adding up the amount drawn by each item at once and making sure it was less than 40.
Yes. That is exactly how you do it. You want more amps available than what you will use. There needs to be some left over to charge the battery.
Originally Posted by Mr87Monty
5. How many amps are used by the engine?
I should know this but I can't remember. I'm gonna guess about 2 to 4 amps for a points ignition. Oddly this is about the same on 12 volt cars.
Originally Posted by Mr87Monty
6. How many amps are required to maintain the battery?
That one's tough. It varies. A battery wont draw much when dead. After it gets partially charged, it will draw a bunch. When it gets close to full, it tapers off. It really doesn't take much at all when the battery is full. If it's down, it will draw everything it can. If there's not much current available it might take a really long time to get back to a full battery and completely normal system voltage.
Originally Posted by Mr87Monty
7. The amp meter appears to work, I only watched the gauge while idling the car. I noticed it was on the charging side and thought nothing of it being steady. Is this how it should be?
The ammeter shows flow in or out of the battery. If it is showing charge it is keeping up, because flow into the battery means there was at least something left for the battery. If it shows discharge, the system is not keeping up. Things will dim, and eventually run down. How fast it runs down depends on how much discharge, and on the amp/hour rating of the battery.
Originally Posted by Mr87Monty
8. I keep the car on a 6v trickle charger with a battery disconnect disconnecting the car from the battery at all times other than when working on it. Is this the best practice?
Yes. Preferably a maintainer, not a plain old fashioned trickle charger.
Originally Posted by Mr87Monty
It is one of the quick connects with a dial to connect the battery. I use the same one for storing my Monte Carlo in the winter.
The ones I have had and seen were crap. I like the idea, but haven't come up with something good enough for a 6 volt car. I'm looking into it.
Originally Posted by Mr87Monty
I am currently in the stage of wiring everything. I am using copper wire (not copper clad) and replacing with the same awg or larger. I was under the impression that a 6 volt system would require a larger wires than a 12 volt system. Is this correct?
Yes. Twice the current (amps) for the same work. Amps being flow determine wire size.
Originally Posted by Mr87Monty
All the wiring in the car was larger than that in my current one so I thought it must be correct. Sorry for the long post. I and my kids are learning as we go. We knew we were up for a challenge getting into this. Unfortunately we seem to spend 50% of the time on the planning, 20% finding parts, 20% working, and 10% wasting time wondering what we just did.
Have fun with it!


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