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Old 01-01-2017, 10:19 AM   #16
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Is that something an electrocution prone idiot with a cheap Chinese multimeter can do or should I get someone else to do it?
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Old 01-01-2017, 10:33 AM   #17
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Easily done (even by my accident prone standards). You should be seeing (Volts DC) 14.x across the battery at 2.5k rpm. This would then drops to 12.x at idle and further drop to 8.x when cranking.

On my 300te the brushes failed (they were 30 years old). This was evident by fluctuating voltage seen in the headlights (bright to dim) and on a volt meter across the battery. New brushes are available from ebay for about a tenner. Have a look at your alternator and see if the brush pack unscrews from the rear. On mine it was two phillips screws, visible from above the car and reachable with a stubby driver.

If in doubt it is worth a try, as when they go, they are dead and they will always fail in heavy traffic, at a major junction, with a fire engine on blue lights, trying to get around you, in the pouring rain.
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Old 01-01-2017, 10:40 AM   #18
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My concern would be for some form of AC or voltage spike breakthro damaging the zener diode/s in the relay. However your OVP may have just died thro old age. These basic voltmeter tests should reveal if anything is wrong.
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Old 01-01-2017, 10:48 AM   #19
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Can't get it up to 2.5k on my own, but at 1.5k it is putting out 14.3, and at idle 13.5v (the battery has been fully recharged though last night). No fluctuation on the voltmeter.

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Old 01-01-2017, 10:51 AM   #20
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If these basic tests check out you probably have nothing to worry about.
You would need a clamp meter to measure the current output.
http://www.aa1car.com/library/charging_checks.htm

Last edited by grober; 01-01-2017 at 10:55 AM.
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Old 01-01-2017, 11:42 AM   #21
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Suddenly realised the diesel is almost out, so rather than run out with attendant b-uggeration factor, I'll do the tests when I next get some diesel.
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