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Intermitent Battery Light


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I had to abort a long trip last week at 100 miles or so in, the battery light came on, along with the ABS and ECU lights. Pulled over, checked belts, fuses etc. all OK. Battery light remained on at tickover. AA confirmed no charging = bad alternator. So, got it back home and left it for a week as I work away from home. Went into garage this afternoon to turn the engine over. Battery OK and it fired first time, warmed it up - battery light still on. Voltage check confirmed no charging.

I then get in and notice the light varying in brightness with the tickover. A quick prod and the light glows much brighter. Another prod to 4k rpm and the light goes out. So I go out for an hour or so, run the aircon, headlights and radio all the way, no battery light. She ran absolutely perfectly. Back home to check the voltages and sure enough the battery is charging at tickover, up around 14v, with 12.7v showing with the engine off. All seems well.

So, should I just put this down to a Lotus foible or should I not trust it on a long trip again before checking the alternator? As others have suggested, could this have been a bad earth somewhere? Anyone have any other ideas?

Edited by hedgerley
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Greetings,

This is a common symptom for a car that sits for long periods of time.

The brushes on the alt get corroded, after running for awhile they

start to work again.

I have seen this several times...

A couple of times the alt takes a dump soon after...

an another car it is still running strong after a few months....

First check for a coolant leak and see if you have coolant driping on the alt.

This is the typical cause of the problem.

Good Luck

-Larry

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Since the battery light went out I've done several long runs and she has run perfectly. Started first time after a week and all voltages are correct. No coolant leaks, all sytems fine.

Interestingly, the headlamps no longer pop up when when she starts, as she has always done since I got her. If, as some suggest, this indicates a low battery, perhaps it was never quite right and this minor episode has cleared the problem altogether. Hope it stays that way.

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Since the battery light went out I've done several long runs and she has run perfectly. Started first time after a week and all voltages are correct. No coolant leaks, all sytems fine.

Interestingly, the headlamps no longer pop up when when she starts, as she has always done since I got her. If, as some suggest, this indicates a low battery, perhaps it was never quite right and this minor episode has cleared the problem altogether. Hope it stays that way.

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Check the main post on the alternator. Occasionally they can get loose, causing intermittent contact or arcing. The problem will eventually recoccur until you identify its source and resolve it.

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The problem has returned, except now the battery light does not come on with the ignition and does not appear when the engine is running even though the battery is not charging. So, I've been checking the alternator out and there are no loose terminals. However, the earth braid linking the engine cradle to the chassis side rails at the right underside of the engine looked badly corroded and was in fact bright green! A quick prod and it basically disintegrated between my fingers.

So, the braid and bolts are now removed and I'll replace them tomorrow. Wondering exactly what depends on this earth braid I re-connected the battery and fired her up. Not only did she start but as far as I can tell all systems are go, except the battery light and no charging scenario of course.

I'm pretty much up to speed on the oily bits but electrics baffle me. Can anyone tell me the purpose of this earth and when sorted, will my alternator spring back to life?

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