MGTF battery problems?

1 month 3 weeks ago #194343 by talkingcars
Does the engine speed rise slightly when you turn on all the heavy draw electrics?


Home to black MGZS180, yellow MGZS180, blue MGZR160, green MGF VVC and red MG Maestro T16.

MG - the friendly marque.

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1 month 3 weeks ago #194344 by sworkscooper
This seems very similar to my TF . When I bought it over 5 years ago it had been through several owners but was very low mileage. I just happened to check what the voltage from the alternator to the battery was when everything was on and low and behold like yours it was low . Being low mileage I thought I would try fitting a voltage regulator to the alternator. Found one one The Bay of E from MG Mania and fitted it . Imeadiate improvement from low 12 volts to 14 + . The TF's engine bay is a very hostile place for an alternator. There is very little in the way of passing cool air for it and the temperatures when running are ferocious. Worth checking the earth's but my money would back the regulator failing .
John

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1 month 3 weeks ago #194345 by rosey

talkingcars wrote: Does the engine speed rise slightly when you turn on all the heavy draw electrics?

Not sure tbh, will check

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1 month 2 weeks ago #194378 by rosey
talkingcars: No the engine speed falls when I switch on the headlights. If I also switch on blower motor to max and windscreen wipers they don't seem to decrease speed any more. Could this be a sign of struggling alternator?
I've found the engine earth strap connection to the firewall has some corrosion so will rectify this before alternator voltage checks.

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1 month 2 weeks ago #194392 by rosey
When I take voltage checks from the alternator, is it ok to just disconnect the plugs at the back, ie will it upset any other circuits?

Thanks

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1 month 2 weeks ago #194412 by rosey
So, engine earth strap and battery earth to body cleaned. Also cleaned up alternator connection. Remeasured current drain with ignition off which was 1.5A on initial connection falling after a couple of secs to 27mA so this looks ok. Battery voltage engine not running 12.3v. Just after starting from cold 14.1v but gradually falling as engine got warmer to 13.73.
Voltage at back of alternator from cold 13.95v gradually falling as engine warmed up.
Switched on wipers, blower and headlights and battery voltage idling 13.2v and at back of alternator 13.8v.
Battery voltage @2000 rpm 13.56v (no change from idle- engine was warm by this time)
Alternator voltage at this time 13.88v. Alternator voltage @2000rpm with lights etc on, 13.77v.

Is it right for the voltage to drop off gradually as the engine warms up, indicating that the battery is charging? Do the voltages look right to people?

Grateful for any help
Thanks

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1 month 1 week ago #194423 by rosey
Grateful for any help. Can I draw any conclusions from these readings or is my best bet to buy a battery isolator?

Thanks

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1 month 1 week ago #194426 by gloscs
A battery isolator is a great cheap investment, used one on my TF for years. Once a battery has gone flat you can be sure it will never be the same. The only other alternative I am considering is a solar panel trickle charger but as I keep my car under a cover I would need to keep it outside the car with possibility of it disappearing 🙄

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1 month 1 week ago #194446 by rosey
Thanks for everyone's help/comments. From the voltage figures im not convinced there is too much of a problem so may go via the isolator route.

Thanks

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