JBreckeen

So, during an event a couple of weeks ago, the machine started reading 14 volts at idle, and the volts would rise with revs until around 5000 rpms it would hit the red area (16ish if I remember). If I keep it under 4000 rpms, the volts would always stay under around 14.5 volts with no problems. Was a bit annoying as we couldn't make max rpm's from fear of frying the brains/battery.

So, to continue the event, we became a hybrid -- disconnected the alt belt, and would charge the battery between sessions. It would make it about 20 mins before needing a refresh.

So, it seemed it was the voltage regulator, and I was happy to find that you can replace the regulator without a new alternator. This morning put it on, and it seems even worse now. At idle it is still at 14 volts (yes checked the whole time with my handheld meter), but it will rise towards the redline even at 2-3000 rpms. Boring.

So, questions: 1. This is a stripped racecar with very little power consumption - is there a minimum amps these things put out? Do I need a smaller alt? A dummy load? (seems stupid to me).

2. Could it be the alt itself, and the voltage reg was not bad and made no difference? I have never had a high voltage failure, but we do have another 944 that I can swap alts . . .

Any other clues?

Thank in advance everone . . .

JBreckeen
'88 951

jpk

Low voltage is usually regulator, high voltage is usually cooked diodes in the alternator. You are not really charging with DC anymore, but the raw AC that the alternator puts out. Swap it out.

The only advantage to going with a smaller alternator is lighter weight. The alternator will only load the engine according to electrical load; if you aren't drawing much current through the electrical system, the engine load is coorespondingly low.

944Ross

Bad grounds?

JBreckeen

Thanks for the ideas. No, not grounds, they look good and I have extra bonding as well.

So, I took it to the local autoparts store and had them test the alt. It came back bad diodes. Swapped an alt from our other 944, and it works fine - so bad alternator . . . boring.

So options. Yes I can buy a new one, or has anyone replaced the diodes? Remember the old days when we used to rebuild starters and generators?

The guy at the autoparts store said that the voltage regulator might have the diode pack in it - is that true? I already installed a new voltage reg and it still is inop. Maybe another bad cheap voltage reg?

Thanks again . . .

JBreckeen
'88 951

jpk

I havn't cracked one of the Bosch alternators open myself, but the voltage regulator is too small to hold the diodes. They're inside the alternator case; most likely on a plate at the back of the casing, behind the armature windings.
There are places that will re-build them for you, but if you can find the parts, there's no reason you can't do it yourself. Replace the bearings while you're at it.
There used to be a shop very near me that did this. I could also get bulk battery cable and connectors there. To bad he retired and closed the shop...