Case study: Low-voltage dead instrument cluster - no alphanumerics & most gauges inop
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09-19-2011, 06:59 AM
Seek to understand,^Value
Location: San Jose, California
Join Date: Mar 2008
Mein Auto: 02 BMW 525i M54 auto 130K
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Originally Posted by
was the charger voltage ever read?
It's still dark outside at 5:30 am but I just went outside to double check the charger current and voltage. The charger appears to be good (even though it was bought in 1982 so it certainly was meant for the older cars before sensitive electronics).
1. The charger open-circuit voltage is about 12 ½ volts DC RMS with the battery out of the loop (which is roughly about 14 volts peak to peak full-wave-rectified at 120Hz based on oscilloscope engravings made in the 80's on the back of the charger).
2. The charger closed circuit voltage, in parallel with that of the battery, is about 13 ¼ volts DC.
3. The battery alone, without the charger, is about 11.4 volts (after being charged for 12 hours).
4. The charge current (after 12 hours on the charger) is reading on the Fluke 75 DMM just about what the gauge on the charger is reading, at about 2 ½ amps (so I think the gauge on the charger is reasonably accurate).
There was one anomaly yesterday, but I'm not sure if I just accidentally changed the scale or if the charger has an intermittent so I can't conclude anything from that. The voltage on the Fluke across the battery while it was charging was off the scale ... but again ... it may have been user error.
I just now shook the charger while making these measurements, and they remained stable.
There is nothing in these measurements that shows any problem with the charger.
Last edited by bluebee; 09-20-2011 at
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