Voltmeter reading?

927 Views 2 Replies 3 Participants Last post by Tifosi, Nov 4, 2007

AlexGS

Discussion Starter · Nov 4, 2007

I took my 164 for a proper drive today - about a 120km round trip, towing a trailer most of the way - and it behaved itself impeccably despite horrible weather conditions - lashing rain, wipers full-speed but not fast enough (clunk-click-clunk-click etc.), foglights going as I seemed to be driving through a cloud.

I wish I'd got the air conditioning fixed sooner, as I was soaking wet so it was difficult to keep the windows demisted. A timely reminder of how useful a/c is, even when it's not particularly hot outside, if it is extremely wet, a/c really helps. I'm getting a replacement compressor rebuilt ready for it.

Anyway I've noticed that the voltmeter sits at about 13V while driving. I noticed that when I switched on the heated rear window (which by the way works 100% now that I've fixed the melted fuse holder), the voltmeter needle dips slightly below 13V. Should this be the case or does this suggest that my alternator requires new brushes? Or is it likely to be an instrumentation fault?

My old (newer) 164 used to sit at nearly 15V on the gauge (maybe 14.4V).

The (fairly new) battery holds a charge very well - before I went away for a month, I removed the battery from the car, dosed it with conditioner and charged it fully, and it was still fully charged on my return. It's been in the car since then and after a few weeks, still cranks the engine well.

Thanks for any input on this before I decide to pull the alternator apart.
-Alex

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Alfisto Steve

· #2 · Nov 4, 2007 (Edited)

No need to pull alternator apart. Just remove rear metal cover (three 8mm hex nuts) and with battery disconnected remove two screws holding voltage regulator and bruxh set in place. Inspect length of two brushes. when new both brushes same length (about 1") but usually one wears faster than other so will be uneven.

I use a $20-25 replacement regulator Made in Brazil I get from my local alternator and starter repair shop.

As for your gauge reading differences between two cars they are probably just that different but OK. Proof is in testing with meter. I have one car that gauge reads high 15v and one that reads normal 13ish but both read about 13.7 - 14.5 when charging with multimeter tester.

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Tifosi

· #3 · Nov 4, 2007

2 cents from the edge of things:

If the voltmeter is reading anything above 12V with a bunch of accessories on, then the alternator and regulator are doing thier job and charging the battery.

If it's reading below 12V with accessories on, then either the alternator can't keep up, the regulator is getting beat, or there's some kind of electrical fault in the system (bad ground or the like) and is letting the battery slowly bleed down it's reserves.

Remember, a 12V battery only needs 12V to keep it charged, or rather keep it from discharging, and anything above that is gravy.

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