Alternator question.

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DaveEFI
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Alternator question.

Post by DaveEFI » Sun Jan 05, 2020 7:04 pm

Alternator with two small terminals - one for the warning light, one (not used) for a diesel tach. Would it damage the regulator to connect the warning light to the tach terminal? My guess is not - apart from the thing not charging until corrected.


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ChrisJC
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Re: Alternator question.

Post by ChrisJC » Sun Jan 05, 2020 9:21 pm

I very much doubt it.

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DaveEFI
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Re: Alternator question.

Post by DaveEFI » Mon Jan 06, 2020 12:04 am

It's odd. I have a very accurate 2 wire LED voltmeter sitting across the battery, and mounted in the SD1 rev counter. Normally reads 13.8v or so with the engine running and a fully charged battery. Noticed it was reading low, and the car hadn't been much used, so put the battery on charge overnight. The next morning, the charger had switched to maintenance mode, so the battery fully charged. And switching on the ignition showed 12.5v on the voltmeter, a few hours after the charger was disconnected. But on taking the car for a run, the voltage hovered around 13v - and at one point went under 13, which I 've never seen engine running before. Was dark when I got home, so I'll check the battery voltage engine running tomorrow with a decent DVM. But the 12.5v engine stopped was what I'd expect which suggests the voltmeter is OK. The alternator was brand new a few years ago, and hasn't done many miles.
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Re: Alternator question.

Post by ChrisJC » Mon Jan 06, 2020 10:06 pm

It does sound like it's not charging.

Is there a signal on the W (tacho) terminal on the alternator? That terminal is connected to one of the three phases and is an AC signal.

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DaveEFI
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Re: Alternator question.

Post by DaveEFI » Tue Jan 07, 2020 4:13 pm

It is charging to an extent. As I've used the car at night for far further than it would run on the battery alone. Just checked the battery volts at the terminal posts with my Fluke DVM. 12.1v ignition on, but engine not started. Very close to what the car voltmeter reads. Car started normally, so battery reasonably charged. Fluke now reads 13.2v at a fast idle as does the car one. And it would normally read 14.1v after a cold start, with no other load on the electrics.

It could be just coincidence after that wrong connection, but my guess is the regulator is now faulty. The alternator was a brand new 100A upgrade from the standard Lucas one, and although now well out of any warranty, hasn't done many miles. Couldn't really see the part number etc, so will have to take it off before ordering up a reg. I can't even remember the series number of it - except the main difference between it and the original is the cooling fan is internal. And the main shaft a different size, so had to get a new pulley.
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