The alternator replacement thread, Fixed! Options

[Spoke]

Damn, that was a tough one. Still don’t know why the grounding issue was happening, as the meter said I was golden. But, clearly, the meter was wrong.

Zach

I took apart an engine once and the alternator had a braided strap on it connected to a bolt on the engine case. You did yours one better by connecting the alternator case directly to the chassis instead of the engine case. I wonder what the D- to chassis voltage is now? If you get a chance, measure D- again to see the difference from the previous measurement.

Looking at the engine w/o the tin it became obvious that all the alternator current flows through the alternator case to the fan shroud, then from the fan shroud to the engine case via the 4 small studs holding the shroud to the case. If the shroud is painted or powder coated, the coatings could interfere with the alternator case grounding causing issues like you've experienced. The alternator brackets if painted/powder coated could also cause resistance. The coatings should be scraped off or masked off during application. Best solution is to run a wire from the alternator case to the chassis.

It's very difficult to get an accurate resistance measurement when the resistance is much less than about 1 ohm. At sub ohm resistances, even the resistance of the probes need to be included. The best way to measure a low resistance like this is to put current through the resistor and measure the voltage.

[VaccaRabite]

Zach,

Are your alternator mounting brackets painted of plated ? I have heard that painted brackets interfere with the grounding.
Is that using the alternator and VR I sold you?
Bruce


@vaccarabite

I’m fairly sure this was the issue.
All the tins and my fan shroud were powder coated. The studs were taped off, but the slider part of the shroud wasn’t. So I’m guessing there was resistance there.

What is confusing is how my meter was showing no resistance. Granted, I was measuring this with the engine off, and maybe that was the problem. It would start showing a little resistance, maybe an ohm, but then would quickly go to 0.000 resistance.

And now I have a collection of spare voltage regulators if I ever need them. Lol.

Zach

[VaccaRabite]

I took apart an engine once and the alternator had a braided strap on it connected to a bolt on the engine case. You did yours one better by connecting the alternator case directly to the chassis instead of the engine case. I wonder what the D- to chassis voltage is now? If you get a chance, measure D- again to see the difference from the previous measurement.

I’m still loosing 140MV, which isn’t much.
And while DF and D+ are set for max effort, I’m now pushing 17 volts at warm idle (1100rpm) instead of the 14 volts I had been pushing at idle.

It’s really night and day after running the big bore ground cable from the alternator to the chassis.

Zach

[worn]

Goddamn happy dance.
14 volts at idle.
14 volts at 4K rpm.
Using either of the single piece solid state VRs. Using the pig tailed solid state VR showed 13.5v. And the mechanical VR I got from Bruce was dancing from 13.5 to 14V.
Zach

Great news. Really glad you ran it down.