Author Topic: Low voltage  (Read 5225 times)

Offline Alex

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Low voltage
« on: July 31, 2009, 08:30:45 pm »
Good news- Stack voltmeter is in, so I can keep an eye on things.

Bad news - Voltage is pretty low, resting at a fluctuating 12V when driving with the headlights on.

Drops below 12V if I'm parked up (engine running) with lights, heater and wipers on, down to about 11.5V.

Some of that will, I guess, be a result of me tinkering with the gauges earlier (switching the ignition on and off a lot) but it's done around 100 miles since so should be fully charged?

The alternator was changed about three years ago, so should still be healthy. Battery is only a year old, so again that should be fine.

Earthing problem?

Offline Alex

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Re: Low voltage
« Reply #1 on: August 01, 2009, 04:17:39 pm »
Been looking through old threads, and generally speaking the advice is to change the alternator.

It's cash I'd prefer not to spend unless I know for sure it's goosed, as that's exactly what I did last time only to find I was getting the same problems. I've checked in the past and this alternator has only ever put out this sort of voltage, same as the last one and the one on the GT.

Which points to wiring, I guess. What bits of the alternator wiring would cause issues? And yep, could this be an earthing problem as I mentioned earlier? Where does it earth to?

Offline g40chris

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Re: Low voltage
« Reply #2 on: August 01, 2009, 06:05:58 pm »
the brushes in the alternator may be worn a bit, might be worth checking that

Offline scotsjohn

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Re: Low voltage
« Reply #3 on: August 01, 2009, 06:50:43 pm »
About a tenner for an alternator brush and diode pack which is a skoosh case to fit(once you've got the alternator out). Can't remember the part number now but they're Bosch generic and any motor factor will sell you one. Dip a cotton wool bud in petrol and clean the slip ring before fitting.

Offline Alex

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Re: Low voltage
« Reply #4 on: August 01, 2009, 11:50:18 pm »
But surely they would've been fine when the alternator was new (and producing the same voltage)?

Offline Alex

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Re: Low voltage
« Reply #5 on: August 02, 2009, 06:02:15 pm »
I managed to get it up to 13V earlier after a decent stretch of clear road with my foot to the floor, and it stayed there till I got home.

Could this be a battery issue? Like it's not holding charge? I do occasionally get the battery warning light come on when it starts up, prod on the throttle and it goes away.

Offline Alex

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Re: Low voltage
« Reply #6 on: August 02, 2009, 07:10:55 pm »
I'll have another look at the earth straps in a mo, the only one I can remember being a bit unwell is the one by the fusebox. We replaced them all when the G40 engine went in.

I've had another check over everything, cleaned and greased the battery terminals and took it out for a spin. It sits anywhere between 12V and 13V most of the time, but usually closer to 12V. I also noticed the hazards flashing makes it jump from 12V to 13V, should they really be draining it that much?

Plugged it into the CTEK battery charger in my garage, which says the battery is fully charged (it'll keep topping it up if it dips though).

I've just fitted a new (to my car anyway) Duostyling air fuel gauge, and according to this from cold it's running fully rich. It seems to run fine (slight flat spot at about 2,000rpm) but the garage who fitted the gauges said the oil was very black, a symptom if it running rich. Low voltage = ECU getting the hump? Possibly a contributing factor to my gauges reading low as well?

Offline Alex

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Re: Low voltage
« Reply #7 on: August 02, 2009, 07:56:36 pm »
Just been out and cleaned/greased all the contacts on the earth straps. The car seemed more willing to start, but no real change shown on the gauge. I'm a bit stuck, I don't want to throw cash at this because (on past experience) it doesn't get me anywhere.

I'll leave it on the CTEK overnight, see what it's like tomorrow. Theoretically, I guess this should fully charge the battery up to 14V.

Offline Alex

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Re: Low voltage
« Reply #8 on: August 02, 2009, 08:04:59 pm »
Correct :)

Raising the revs to about 2,000rpm doesn't seem to make much difference compared to idling. ???

Offline Alex

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Re: Low voltage
« Reply #9 on: August 02, 2009, 08:20:53 pm »
In which case, yes it must be the alternator. Still leaves me a bit confused how I changed my previous duff alternator for a brand new one which does exactly the same thing. Unless I've been diddled at the garage (wouldn't be the first time) and they've used a second hand one.

I think before I actually put any money in the direction of this car I'm going to let someone have a look over it in person though. Alternators are expensive, and I'm not fitting the fucking thing myself so there's labour to budget for. Even if I just change bits of the alternator, I still have to pay that.

Offline hayesey

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Re: Low voltage
« Reply #10 on: August 02, 2009, 09:31:29 pm »
I'm half asleep after the polo show so sorry if you've already said this and I've missed it but have you tried putting a multimeter directly onto the battery terminals and read the voltage there?  You will get a bit of voltage drop just reading the gauge wired up to the interior loom

Offline Alex

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Re: Low voltage
« Reply #11 on: August 02, 2009, 09:52:50 pm »
Everything in this thread is off the gauge, but I know I've investigated before with my multimeter (which is back in Cardiff atm) and it's been low for as long as I can remember.

The alternator's definitely new though, there's a little metal bracket which is not attached to this one and was attached to this one. And the old one had a blue label on it, plus was dirty. This one is at the very least a reconditioned one.

Offline G40supercharged

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Re: Low voltage
« Reply #12 on: August 03, 2009, 06:26:48 pm »
I can't remember exactly how alternators work, but the voltage sense wire is connected through the red light on the dash. This doesn't just tell you it's charging/not charging but is involved in the voltage level the alternator generates. If this is broken, the alternator doesn't work at all (i think it's a thin blue wire). It could be a bad connection through this wire that is affecting the voltage generated.

Offline Alex

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Re: Low voltage
« Reply #13 on: August 03, 2009, 10:21:46 pm »
That's possible, how easy is it to get to? I swapped to G40 clocks about a year before the conversion.

Offline Alex

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Re: Low voltage
« Reply #14 on: August 04, 2009, 09:18:15 am »
Dunno what it is tbh, but I'm assured it's not needed. It looks like a metal clip to hold the wiring in place. I'll get a pic later.