Battery won't hold a charge. Have to jump it to get it running.

With engine running at minimum load, I get 12.6 V across the + and - battery terminals (dips to around 9 when the radiator fan come on). At the same time, I get 13.6 V measured at the alternator - but it won't go above 13.9 even with the engine revving and with minimum load.

I can't find a problem with the wiring, so I am thinking (having read the entire section in the FAQ page) it's the alternator.

This evening I removed the voltage regulator to see if the brushes were worn out, but I am not sure how to tell for sure. How can I tell? Is there a good site that explains how to tell?

If the brushes are OK, should I replace the entire alternator? Based on the symptoms, would you agree that the alternator or regulator is the culprit? TIA

Regards,

Calvin (92 940GL 198K, 96 850 Turbo 97K)

You are getting too much voltage drop in the harness for some reason. Make measurements across every joint to locate the bad spot.

My car had a bad crimp on the lug at the alternator which I'm sure pushed the PO to sell the car faster. (After a start while the battery was recharging I had about 0.5 volts form the alternator stud to the wire just after the lug.) When I got it, I imeadiately started to have "no-starts" due to a dead battery. This was exacerbated by a headlight wiper motor that was broken and often didn't "park", so it kept running. I cleaned and soldered the crimp lug and while I was at it also replaced the regulator/brush assembly. With a new wiper motor I've had no battery problems for 5 years now.

There should be less that 0.2 volt drop from the alternator to the battery + terminal. You are reporting about 1.0 volt. Also check from the battery - to the alternator body for the same requirement.

The 13.9 seems OK if measured after the alternator has warmed up some. A cold alternator should probably be around 14.5 volts.
--
'96 965 with 16' wheels at 119K. Had '85 745 Turbo Diesel for 200K.

THANKS! You've given me good things to check further. I read that about the dash light in the FAQs, but forgot to check it!

I am getting about 13.6 cold at idle at the alternator and peaking at 13.9 when revving high (guessing up to about 3500+ RPM by the engine sound). I thought the voltage should increase with RPMS until the regulator caps it. My three other cars (SAAB 9-5, Toyota Previa, and another Volvo) all measure about 14.5 (cold at idle) across the battery terminals. This makes me think I need to replace the regulator/brushes. What do you think?

If so, then the 1 volt difference at the alternator versus the battery that suggests the wiring problem you identify would be a SECOND problem. Does that make sense to you?

TIA, Calvin

If you are getting a 1 volt difference between the alternator and the battery you definitly have a wireing problem.
--
'96 965 with 16' wheels at 119K. Had '85 745 Turbo Diesel for 200K.

How long did it take you to drive to work? After a run flat I would think it would take a good 1/2 hour or more of highway running to get the battery recharged.
--
'96 965 with 16' wheels at 119K. Had '85 745 Turbo Diesel for 200K.

hmmmm, I let it idle for about 40-45 minutes, thinking that would do the trick. But if the voltage at the regulator does increase much at higher RPM, would that really make any difference? I may be missing something here.....

After paying $250 to an independent mechanic to diagnose a similar problem, here's what I would do to save myself $250

Check for continuity for that red/D+ wire that runs between the alternator and battery.

Does your battery/idiot light come on when you turn the ignition on? That pesty light is in series with the alternator. If it's burned out, your battery will not charge.

Check the wiring to the dashboard. Mine was loose and was the cause of my battery not charging. I confirmed this by checking voltage at the battery with engine on and wiring connected; then I disconnected the wire and saw the alternator not charging the battery.