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MG Midget and Sprite Technical - Alternator output

What controls alternator output, assuming a standard diameter pully? Would 15.8v damage a battery and can this output be adjusted or is something faulty beyond repair?

(Apologies, but I should add this isn't actually on a MG related, it's on a 205 Gti Pug)
GuyW

Conventionally, alt output is controlled by the inbuilt regulator, which rapidly switches the output on and off to achieve around 14v when connected to a 12v battery. 15.8v is high and would worry me in terms of overcharging the battery but I'd like a second/ third opinion as to if it will actually boil the acid and overheat the plates.
Bill Bretherton

Thanks Bill.
Is an overcharging alternator likely to be fixable? I'm not sure, but l think this was a replacement one fitted last year.
GuyW

Guy,
I know its not Lucas but if you've got the time these JT vids will cover the principles.

223 MG Lucas Electrix: The Alternator, Part One -
https://www.youtube.com/watch?v=lPmk2FXs_18

226 MG Lucas Alternator II -
https://www.youtube.com/watch?v=TMgRfToSiLY
Nigel Atkins

Guy,
On boats we often use smart charge controllers such as Adverc's etc, theese are computer charge controllers that even measure battery temperature etc.
They never allow the voltage to exceed 15volts for a 12volt system to avoid damaging the batteries (although some of the varying charge cycles get up to about 15volt).

It would appear that the regulator pack on the alt is faulty - if you have an old fashioned autoelectrician they may well be able to fix it but the throw away world may find it cheaper to replace.

R.
richard b

Guy, I've replaced regulators on older Lucas alternators in the past e.g. MG Metro. E-bay list a Bosch reg for the 205 GTI for £10 but I suppose it depends what make of alternator is fitted, compatibility across makes etc.

The regulator is not adjustable - it is a semiconductor that maintains a fixed voltage.
Bill Bretherton

Thanks Bill. Car is my son's. He has sourced a replacement alternator and a new battery now. Sounds like the high output had cooked the battery plates as it wouldn't hold a charge even when disconnected.
GuyW

This thread was discussed on 07/08/2018

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