8A-14 ChargeCircuit.jpg
I have a 1980s SBC with a 10SI alternator. Allegedly 63 amps (this may be important). Stock replacement alternators for the application, charge system wiring is stock config. For years now, it's had a thing where you can drive during the day as long as you want and everything is great but drive at night for an hour, shut it off, and it won't restart. Low battery. Letting it cool off doesn't bring it back so it's not a hot starter, battery has to be charged.
It's had multiple different parts-store alternators on it and multiple different batteries. Wiring is good. No-load charge voltage is higher than it should be: 14.80V. No-load voltage decreases a little as RPM increases. With all the loads this old car has the most I can get out of the alt with a clamp meter is ~38 amps. Under max load output voltage falls off to 13.5ish. Increasing RPM does not increase current output or voltage. It's just as bad cold as it is when hot, there's nothing I can do to get more than 38-39A out of it.
Voltage drops are fine -
no load (~12A)
BAT- to alt case 20mV
BAT+ to alt output stud 40mV
full load (38A)
BAT- to alt case 50mV
BAT+ to alt output stud 180mV
Is this just junk parts store alternators and they're all using the cheap innards from the optional 43A units? That's sure what it acts like to me. I can't find any other problems. This is completely academic, I have a new 140A CS144 in the mail to do a conversion. It's just always bugged the piss out of me and I want to know WHY YOU NO WORK RIGHT.