Alternator upgrade HELP!

[Daryl]

My 1990 SN has (had) a 35 amp motorola alternator on it and it wasn't outputting enough amperage (half maybe)

this alternator has the regulator mounted on the rear of the unit.

so i took it to a local shop and he sold me on a new one (upgraded to 65A - internal regulator)

when i got it back, i hooked up the power wire and the wire that was in the connector (is this a field wire or voltage sense wire?)

now the boat won't shut off with the key or the ignition switch. (after pulling the alternator output wire the boat shut down)

The wire in the connector (field wire from above?) shows power when the key is in the RUN position.

seems the alternator guy is a little puzzled......

Comments??????

P.S. boat charges great! but this small run-forever issue is sort of important

[surroundsound64]

RE: Alternator upgrade HELP!

Weird...

On the alternator poles you should see markings like "pos", "neg", "A+". This will tell you what the other wire is that you asked about. If it says A+ it's the field wire... I can't remember what the other possibilities are. Go look and if you have and questions post them.

[DavidF]

RE: Alternator upgrade HELP!

Seems to me your backfeeding the ignition directly from the alternator. Will the engine start, run and charge with the wire in question disconnected?

[bobchris]

RE: Alternator upgrade HELP!

was the new one made for your application? I would suggest getting a new wiring harness from SKIDIM that they sell when the electrical system is up graded.

[Daryl]

RE: Alternator upgrade HELP!

well... here's the scoop... after some research - and some trial and error - i returned the alternator and got my money back.

the issue is that the excitation wire needs to have a diode in the circuit to make it work right.

since the first "alternator guy" couldn't help me - i went to another one.... I will know tomorrow if this new "alternator guy" knows what he's talking about.... I think he does.

I was trying to tell the first guy he needed a diode to isolate the alternator but that seemed to be over his head. He understood the concepts but could not make the leap to application.

DavidF - you describe the symptom.... if I disconnected the excite wire - the boat would start, stop and charge - but no (or low) charge at idle. I figure that once the RPMs on the alternator got high enough it would self excite and all was good. But at low rpm - no charge.

[DavidF]

RE: Alternator upgrade HELP!

Well, then you are indeed backfeeding the ignition, so a diode would prevent the current from flowing backward to the ignition. Still, this seems strange.