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There is a place for upgraded alternators, not saying they don't belong at all. But this person is trying to diagnose a charging problem, go back to basics and solve the problem.
< I agree with this. Before he gets out his checkbook, he will do well to troubleshoot the reason it is not working correctly now, before throwing parts at the problem.
However: if his troubleshooting reports back that it IS the alternator - then get a modern upgrade while you are at it. You will be much happier with the end result.
Hi Eugene,
It sounds like your alternator is not charging properly. They do go bad with time, and can be repaired, rebuilt or replaced with OEM. I went the high output route with Carl's unit about 9 years ago. I did this because I added a supercharger, which involved removing my belt driven fan and adding multiple electric fans. My OEM alternator was never designed for that scenario, so I needed more juice. That said, my alternator has needed two repairs in that time, each was relatively cheap and easy to send the unit off to the original builder.
If I had a stock electrical load situation, I would explore replacement OEM alternator, after confirming your diagnosis. The OEM's seem to charge slightly better at idle, and have adequate output at speed. They are significantly cheaper as well.
Obviously it's your choice, and it's fun to have the latest technology sometimes, too.
Good luck,
Dave
Again, thanks so much for the input. First thing I'll do when I take the car out of storage is to check the voltage at idle. If low, then I'll replace the alternator. Unfortunately, the last alternator change didn't make a difference, so I'll call Carl.
I have one of Greg's alternators. Buy one and forget about charging problems, also replaced my battery with a AGM sealed battery. My car has sat for a year, with the cables disconnected, and starts right up once everything is reconnected.
Don't just plan to replace the alternator - test the exciter line to see what is happening. If there is a problem with the exciter line a new alternator may not charge either (and there may in fact be no problem with the old one - unlikely but possible). Always best to do the diagnostics (you can start by checking the charge light on the dash and testing the exciter line at the 14 pin engine harness connector.
I would actually start with checking the accuracy of the in dash gauge to the voltage at the B+ post at the right side front of the engine compartment.
I would actually start with checking the accuracy of the in dash gauge to the voltage at the B+ post at the right side front of the engine compartment.
+1 on that. Don't trust the in-dash voltmeter. Mine has good days and bad days, but when I check voltage with multimeter, everything is good.
+1.
928 101 is don't trust the dash voltage gauge. Always check voltage at the jump post. The gauge gives a relative number and is good for quick comparison.
Good luck,
Dave
When I did my Spyder build I brought runs of heavy gauge wiring from the battery to the center console to support the auxiliary fuse box I installed. One of the things I put into my new console setup was a 12v cigarette lighter socket. Using a USB charger in that socket that displays voltage and current device amperage draw has it showing a full 1v-1.5v higher than what the voltage gauge in the dash shows.
Socket is to the right of the outside temperature gauge
Don't just plan to replace the alternator - test the exciter line to see what is happening. If there is a problem with the exciter line a new alternator may not charge either (and there may in fact be no problem with the old one - unlikely but possible). Always best to do the diagnostics (you can start by checking the charge light on the dash and testing the exciter line at the 14 pin engine harness connector.
Alan
^This. Not terribly surprising that the best advice in an electrical thread came from Alan.
Is the alternator charging? It sounds like it's not, but make sure. As was noted, don't trust the dash gauge. A DVM is an essential piece of equipment for an intelligent 928 owner ("Intelligent" meaning "doesn't just call a shop to fix everything").
As Hacker noted, the 'el cheapo" Harbor Freight one is adequate. It's available as a "Free with any purchase" item, like the batteries, flashlights, screwdrivers, tape measure, ect.
Put the meter on the hot post or the battery itself. You should see above 13v when it's running with minimal load (lights, fan radio off).
I would guess the alternator is not charging, from your description.
If not, why not?
Is the alternator itself bad? Most FLAPS will test them free of charge.
Is it the voltage regulator?
Is it the exciter circuit?
Is it something else?
As Alan noted, does the alternator warning light come on when the key is on, but before the engine is started? If not, that itself will screw up the charging circuit.
03-07-2019, 02:18 PM
