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Voltmeter slow to register - normal?


Steve4012

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My voltmeter gauge stays in the red at about 11v for the first couple of miles of driving before rising to 14v for the next mile or so. It then settles at 13v or just below from then on. Never had battery problems so not too bothered but just wondered if it's a 'they all do that' or not.

Thanks, Steve.

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I say, it's your early warning of impending alternator failure. :X  Although, it COULD be a loose or worn V-belt that doesn't 'drive' the alternator sufficiently until things warm up.

 

The second scenario could be a result of a too-narrow V belt (I installed one of those once).

 

Our 'properly working' Bosch alternator charges nearly 14VDC on the gauge within seconds after a cold start, and settles down to 13.0 - 13.5VDC after a few miles of driving.

Edited by CarBuff

Atwell Haines

'88 Esprit

Succasunna, NJ USA

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Many thanks CarBuff, will keep an eye on it. It doesn't seem heat related as if I switch off engine then restart it's back to the same until it perks up again a few minutes later. Any other feedback as to whether others have experienced this would be welcome.

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My 1982 turbo with a new alternator also does this....takes a while to register properly on the voltmeter. I think the movement is damped, as it also takes a long time to return to the stop once the engine has stopped. As it's done this since I bought the car in 1988 I don't worry about it!

Scientists investigate that which already is; Engineers create that which has never been." - Albert Einstein

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5 hours ago, CarBuff said:

Might be the difference in Smiths VS VDO instrumentation, then.

Could very well be...

Scientists investigate that which already is; Engineers create that which has never been." - Albert Einstein

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I've just put a new (Lucas) alternator and vbelt on mine, the needle comes up slowly, but I'd say less than a minute.

Have you put a multi meter on the battery to see what's REALLY going on? 

If the multi meter doesn't instantly register 12, and rise to 14 under a few revs then you know it's definitely not charging as is should, and you can avoid an impending breakdown.

'82 Turbo Esprit

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  • 1 year later...

Just thought I'd add to this thread as it's now solved, in case anyone else has the same trouble. I received no charging from the alternator on start up but I discovered that it started working fully when I exceeded 3000 or so revs. I also belatedly noticed the battery light did not illuminate with ignition on. The 'excitor' wire (the small brown and yellow wire) was not attached to anything. I put this on the post on the alternator and the battery light now came on with ignition 🙂 but stayed on and still no charge unless revved 😖

After a lot of messing around, I then spotted a spade terminal at the bottom of the alternator almost out of sight with another post terminal so put the excitor wire on there and bingo, light on with ignition, light off with engine start and full charge straight away. Incidentally, the post terminal I tried first which didn't work is in the same position as the correct one on my 81 turbo so it's very easy to conclude the alternator is duff and not notice the correct connection underneath at the bottom of the alternator. Hope this helps someone. 

 

20190901_200540.jpg

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That is bizarre!!

Only this afternoon did I spot the same behaviour on my voltmeter for the first time!! 

I removed and refitted the alternator last month and now suspect this little wire. I'll check tomorrow - cheers!

BTW, what does the excitor wire do?

"Intellectuals solve problems; geniuses prevent them." Albert Einstein

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basically provides enough current to the field winding to start the alternator working. Otherwise it relies on residual magnetism to kick things off, and as noticed this typically happens at higher revs, if at all. Once the regulator can feed back volts to the field winding to keep things in balance, the exciter current is not needed, hence the light goes out. The regulator basically balances the field current with the actual car's current demand and keeps voltage at correct value.

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My Europa Special exhibited this behaviour straight from the factory in that after starting the ignition warning light didn't go out until you revved the engine to about 2000 RPM . Always wondered why but as it never caused a problem with battery charging I never did anything about it, now I know why. :thumbup:

Cheers,

John W

http://jonwatkins.co.uk

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