The Stovebolt Site Forums The Shop Area The Electrical Bay Appropriate Alternator Wiring

It's been a while since I've made any improvements on my truck and I'm getting the bug to work on it again. I'm tired of the lights dimming every time RPMs drop to an idle so I'm thinking of replacing the generator with an alternator and I'd like to avoid burning up the wiring harness.

The trucks a 1953 3100, but the electrical has been converted to 12V negative ground. It still has the original gauge wiring so the wire running from the generator to the voltage regulator (and ultimately to the battery) is 10 gauge. So far the wiring has handled the higher voltage without any problems. But the new alternator is rated at 75 amps. So, my question is can the 10 gauge wire handle the combined higher voltage and amperage or will I have to go to a larger diameter wire?

Your 10 Ga wire is fine. Remember that the higher the voltage, the smaller the wire has to be to carry the same power, therefore the same wire can carry twice as much when you go from 6v to 12v.
Your problem is going to be the ammeter. You can't put that kind of current through a 30 amp meter. I always like to change to a voltmeter and remove the high current wires from inside the cab completely(single wire alt run directly to the starter post).
But if you don't want to change things, you have to connect a shunt across the ammeter so that 2/3 of the current bypasses the meter. It will still indicate if the system is charging, but the numbers won't be right.

A print-out of the discussions here about ammeter shunts would require several reams of paper, and firefighters' turn-out gear to survive the flaming that has gone on!

A shunt can be as simple as a strip of stainless steel connected across the back of the ammeter, or as complex as an engineer's wet dream- - - -"Ya pays your money and ya takes yer choice!" Thousands of 30 amp meters have been run without a shunt for millions of miles, carrying alternator output without burning up vehicles, so the whole discussion is sort of an exercise in semantics. A pegged ammeter might not be accurate, but it's not a thermonuclear device ready to explode!
Jerry


Jerry

Thanks for the advice and the warning. I definitely would have burned out the ammeter - and I’m really trying to avoid starting a fire.

I see that there are already articles and discussions on voltmeters and ammeter shunts so I'll use those as a guide on how to complete the project.

I didn't worry about shunting my ammeter.. it smoked immediately after I turned the key on the first time (12 volts). I installed a small 3 gage panel for fuel, amps and temp.

Ignorance and cheapness save me (and, my 1954 ammeter) when I changed to 12v and a cheap 35-amp 1-wire alternator in 1997 (on one of my 1954 pickups).

Why a 75 Amp Alternator? My 35 Amp works fine and no worry about the Amp gauge