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Ammeter behaviour and ignition light on questions

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Old 01-12-21, 08:15 PM
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Default Ammeter behaviour and ignition light on questions

My car has an alternator with an internal regulator fitted in place of the original dynamo and regulator. Recently, the ignition warning light has refused to go out. It glows a bit all the time. I read that is an indication that the charging system is not working and there being an imbalance between the voltage coming from the battery and that from the alternator.

I checked the battery - 12.6V when the engine was off. 14.4V when the engine was running. So, those seem to indicate battery and alternator are working. Then today, driving, I noticed in a short distance today (say 3miles) the ammeter read as follows (all readings are approximate)

Ignition on, engine not running 0A
Starter engaged -20A
Engine running at idle - +20A
Driving +20a then a sudden drop to 0A. A few minutes later it was back at +20A then it dropped to 0A again, then up to 15A and stayed there until the engine was turned off.

I don't have experience monitoring an ammeter but is that normal? I'd expect it to stay + charging and gradually drop to 0 as the battery became recharged not drop to 0 then jump back up.

Any insights into this behaviour and/or the dimly glowing ignition light would be appreciated. Thanks.

David
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Old 02-12-21, 05:58 PM
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Feeling a bit foolish here but the ammeter behaviour seems to be caused by the electric fan. When it's running the ammeter swings to +20A and drops to approx. 0A when the fan cuts off.

I still can't figure out why the ignition warning light stays on though!!!

David
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Old 03-12-21, 10:35 AM
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I’d suggest checking the “earth” straps between battery and chassis and chassis and engine with considerable care as this is usually the cause of odd (and in your case extremely odd) electrical problems. A quick diagnosis might be achieved by connecting the alternator casing directly to earth using a jump lead. And also check the live battery lead. It sounds to me as though a high or perhaps a slightly intermittent resistance in one of the main feeds to or from the battery may be behind the issue.

Why, oh why, did people used to put the engine "earth" lead in the most inaccessible possible place?

Also be aware that an alternator seems to be capable of overcoming a high resistance in the battery charging circuit, which of course includes all the above straps and leads, by winding its output voltage up, notwithstanding any internal or external regulation. But the end result is that it both overcharges the battery (one can’t actually get a battery voltage beyond a certain point, but I hope you see what I mean) and is perfectly capable of burning its internal insulation out. I don’t claim to fully understand the process but have experienced it - I went through three alternators rebuilds before I got to the root of the problem.
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Old 03-12-21, 10:43 AM
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I think Roger is right, it's most probably a faulty earth connection. It would be a idea to put an earth straight from the alternator to the attachment bracket . The output from the alternator does seem to be very high, this may be caused by the earth problem or a faulty diode pack. To be honest I if your earth leads are good then I think it is the alternator, which would also account for the ignition light glowing. best of luck.
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Old 03-12-21, 07:04 PM
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Thanks, gentlemen. I'll try digging in to the ignition light issue again this weekend.

David
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