Hello! I've converted my 32 Ford from 6V to 12V using a rebuilt 1939 generator. It will charge approximately 40ampere. I want to use the stock 32 ammeter, so first of, can I do that even though I'm running 12V? And second, how do I wire it? I've looked at some old and new wiring diagrams and they are not similar. My guess was to run one wire from the battery side of the solenoid to one side of the ammeter and then run the other side of the ammeter to "battery" on the regulator. Is that correct or am I completely wrong? Thank you for your help! Simon
It only reads 20 amps so I guess not.. I was told once that you can put a reasonably sized loop between the contacts on an ammeter if it's made for a lower amp, but that sounds a bit sketchy. Thanks for your reply
image from Van Pelt Sales. One side of the ammeter connects to the battery, the other side connects to everything else on the car (except the starter, and perhaps the dome light). What else on your car is different from original? if you gave is more info about what you're working we, we could maybe help better. The current that an ammeter can withstand, is an interesting subject...so is the current that a generator produces, and how much of it goes to the battery, vs. the other loads on the car, and under what conditions. I would not be so quick to rule out the use of an old ammeter because the generator is rated at 40 amps. But I might rule it out for other reasons!
I'm running a 59A, crab distributor, heavy duty ignition coil, 12V bulbs around, H4 in front. That's about everything that is changed. The generator is a NOS 39 anchor and the guy who rebuilt it claims it will charge up til 40amps at 2200rpms. Thank you for the diagram!
An ammeter is usually is set up to read the voltage drop across a set resistance in the meter. The current has to run through the meter to do this unless there is an external resistor [shunt]. The shunt has to be designed to work with the meter to read the proper values. A generator that provides more current or a short circuit that draws more current than the meter is designed to read can cause the resistor to get very hot.
No, most meters use the D'arsonval type movement and they work off the current measured. Whether it's 'calibrated' for volts, amps, or ohms, it's the same movement. Many contain internal shunts to attain that calibration; virtually all D'arsonval ammeters and ohmmeters use shunts, which on a multimeter are switchable to attain different meter ranges. That's an external shunt and isn't uncommon, but getting the right size/resistance to maintain any sort of meter accuracy is much harder than you think. You'll very likely need laboratory-grade meters to attain the correct shunt size.
but the ammeter in an old car doesn't need to actually be accurate, does it? it could say D and C and that would be enough for me, as long as I know where zero is.
Some 32-34 pickups (8 cyl?) came with amp gauges that are identical to yours in appearance except they read 0-30 amps. I've seen some with chrome bezels and others with brass bezels painted black.
So just to clarify you have a NOS 1939 generator, that you had rebuilt so it now puts out 12 volts instead of the 6 it was built for, at 40 amps. Is that correct?
Attached you will find a picture of the "bit sketchy" loop of wire across the terminals of the ammeter in my AVATAR, it works fine and as you can tell by the patina has worked fine for many years. Be sure that the wire gauge of the loop is large enough to carry all of the load in case your ammeter fails. If you want to fine tune the ammeter reading play with the length of wire in the loop, but as squirrel said, accuracy isn't that important. Running two identical wires of the same gauge (and each heavy enough to carry all of the current in case of an ammeter failure) from the battery side of the solenoid to the ammeter and then connecting one to each terminal would probably be the quickest way to cut the reading of the ammeter in half (which is what you are trying to do). Since the '32 didn't have a solenoid I assume your wiring has one and that point is where the current goes to the battery. Don't waste your time looking for an original 30 amp gauge. As an off topic note, those cell phone cameras are great, my DSLR camera wouldn't begin to fit behind the dash of my car. Charlie Stephens
Yep that's all I'm concerned about. My 37 Buick, 56 Chrysler, and 51 John Deere all have shunts across the original ammeters. I experimented with different lengths and gauges of wire/shunt to get them to read something I could understand.
Well, that's the owner's call... but if the gauge doesn't give accurate information, why have it? I used to own a '64 Comet; factory 289/4-speed car, when I got it had the stock electrical system except for a basic aftermarket AM/FM/Cassette radio. It still had the OEM 30 amp generator (which I had rebuilt) and factory ammeter. Keep in mind this car had four headlights and taillights, so the electrical load was more than most cars. One dreary winter night (near-freezing temps outside, heavy rain, and overcast so virtually no moon/star light) I had a several hours backroads trip home. So I'm running every electrical device the car had; high beams to see, heater to try to stay warm, wipers, and radio for entertainment. Also on the brakes (lights) a lot, as these were nasty curvy roads that I wasn't familiar with. About an hour into the trip, I noticed the lights seemed a bit dim but the ammeter showed no discharge (or charge either). Ten minutes later, the car started missing and the lights were noticeably dim now. Still not showing a discharge.... I switched off the high beams, turned off the radio and heater and the miss disappeared and a slight 'charge' appeared. By jockeying between the heater and high beams, I made it home with no further incident, although when I pulled in the driveway and shut off everything the charge jumped way up. The car did start the next morning, but was a bit reluctant... and showed a large charge for about 20 minutes before settling back to zero. Up until then, I assumed the meter was reasonably accurate. It showed a large discharge if you turned on the lights without the car running, and showed a large charge right after starting. But truly accurate it was not.... So, does accuracy count? It sure does to me. Within a week the generator was gone, replaced with an alternator and I had no further issues.
Yup, it takes a very rare combination of events to make it so your ammeter didn't do what you needed it to do. You would have been better off with an idiot light. That's what I have in my car!
Idiot lights merely tell you if the system is charging or not. Mine was, but just not enough to cover the full load under what was extreme conditions. It also didn't help that Ford fitted the car with a barely-adequate-under-normal-conditions charging system. The basic lighting load was a bit over 15 amps on high beam, not including the dash lights or gauges. That leaves you with about 14 amps to cover the wipers, heater, and ignition. Brakes lights bring another 9 amps to the party...
Thank you very much for your help, installed both an idiot light and the ammeter with a shunt wire and so far everything seems to work fine. Thanks again!
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