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Old 09-19-2011, 05:25 AM
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bluebee bluebee is offline
Seek to understand,^Value
Location: San Jose, California
Join Date: Mar 2008
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Mein Auto: 02 BMW 525i M54 auto 130K
Originally Posted by JimLev View Post
too long for me to sit thru
Hi Jimlev,
This thread is a pictorial thread, just about the battery, as I like to take things one at a time and have some fun (and learning and teaching) with it.

The 'real' problem-solving thread is this one, as you alluded to:
- Warning: I charged my battery today & apparently killed my instrument cluster & MID

But, for here, this is the response:
Originally Posted by JimLev View Post
was the charger voltage ever read?
Many years ago, I had placed it on an oscilloscope and engraved on the back what I found (which was a 17-volt wave, peak to trough, above ground), at 12 volts RMS at 120 Hz being the output. Clearly there is a simple wheatstone-bridge like diode arrangement that flips every other oscillation of the 60 Hz input. There was a 25 Hz +/- 1.175 volt AC component superimposed on the DC (i.e., 41.5 msec in period); so it's not a "clean" waveform, by any means ... but it is sufficient to charge batteries for vehicles in the 'olden days'.

I no longer have access to an oscilloscope, but the RMS readings from my decades-old Fluke 75 bear out that the charger is apparently still working to spec.

Without the battery in the loop, the 25-year-old half-wave charger reads 12.52 volts RMS, open circuit.
I bounced the unit around and it still read the same (I shook it and tugged at all the wires).

The battery, after charging since about 6pm (almost 12 hours), still reads only 11.39 volts (so it's obviously not taking a charge).

When I hook the charger to the battery, the battery climbs from 13 volts to about 13.3 volts (give or take as it bounces a bit & climbs slowly).

And, the current on the meter seems to be accurate based on the Fluke DMM doublecheck:

Originally Posted by JimLev View Post
Turning the key on seems like it might have been what killed things.
I don't remember if I left the key on when I was charging it. I don't think I did.

I had left the key on after I checked the mileage on the odometer; and that's what (I thought) killed the battery.

But now, I simply think leaving the ignition on just clued me into the fact that I had a suddenly-bad battery.

Originally Posted by JimLev View Post
I always charge the battery while it is connected, never had a problem.
In the past, so did I. Now that I may be facing a very expensive (and tedious) repair, I'm not so sure I would recommend that moving forward.

What I need now to do, when it gets light, is to check the rest of the fuses - but that's for a whole 'nuther thread!

Last edited by bluebee; 09-19-2011 at 10:20 PM.
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