Fw: quattro digest, Vol 1 #2836 - battery drain

[george mills]

Larry wrote:
>Engine on, accessories off. Read voltage, it should be between 13.5 to
>14.5V. If so, alternator shows promise. IF higher than battery, system
>will, in this condition, apply a charge to the battery. IF higher than
>14.5 V, the voltage regulator may be fried. Problems with this are,
>though it'll charge the battery, it will OVERCHARGE it, causing lots of
>hydrogen venting, frequent need for water (to replace the hydrogen),
>shortened battery life, and, depending upon some ECU electronics (ones
>without internal regulation) potential risk of ECU failure due to
>overvoltage/current.
This is certainly possible. However, I have a little story to tell :)
Whilst driving in the boonies last summer/fall? (time flies when yur
havin' fun) I got the dreaded alternator warning light on the
autocheck (nice battery icon). Checked the CC head for voltage and it
showed ~17v! Started turning on accessories to see if this would
change and with all the heavy users (ie headlights, rear window
defroster, blower fan on high, AC on, etc.- wipers were already on
because of torrential rain) I got it down to about 14.5v. I was about
10 minutes away from a buddy and stopped there. Was about 100km from
home base at this point. We fooled with it a bit but it was raining
too hard to really get serious. What I ended up doing was getting a
fully charged battery from him and continuing on with my travels.
About 10km into the trip home the alt. died. About 10km from home the
batt. died and I connected the other one to finish the trip. I had to
turn the lights on for the last 20km because it was getting dark, plus
the wipers were going pretty much full time due to the rain.
I figured it was brushes/regulator and on inspection the unit seemed
OK, but I swapped in new anyway. Still no alt. Put the old unit back
in and took the alt. down to the local trusted re-builder and it was
putting out an erratic 25 amps. on the test bench. Time for rebuild.
New bearings, stator/rotor. Diode plate was good as was
brushes/regulator unit.
I don't really know for sure why it started putting out over 17v with
a good regulator, but my guess is the windings began to short out on
either the stator or rotor or both. BTW, nothing was fried in the
electronics dept. - TG.

Best regards,
Geo