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MG MGA - Generator Issue...help plz

Generator was not working. I found one of the brushes was sticking. Fixed it, put it back in. Cranked it up and out went the ignition light. 13.5V at the battery at high idle. Yay, it works. Turned off the key, ignition light came on, with the ignition off and the key out. Went to look in the archive. Came back and electrical fumes filled garage. I disconnected the battery and checked the gen. It was hot like a coffee pot.

I'm thinking my field coil is grounded somehow.

Your expertise is greatly appreciated.
Judd Irland

I think you will find that one of the solenoids in the voltage regulator box (the cut-out) was sticking down causing it to short through your generator.
Disconnecting the battery cuts power to the regulator cut-out and stops the current shorting through the generator.
You probably heard it click when you disconnected the battery.

You may need a new voltage regulator but it may just have been a temporary effect of your generator brushes coming adrift.

Either way I would test your generator and check the wiring to it for damage also.

This happened to my car on occasion after I converted to an alternator but fortunately I had a battery isolator under the dashboard and was able to cut the power before any damage was done.

Im no great auto electrician so you would do well check on Barneys website for the correct answer to this.

(Also I would definitely fit a battery cut-out switch, it could save your car)

Colyn
Colyn Firth

It sounds as though the cut out in your voltage regulator did not open when you switched off the ignition. With the ignition off the cut-out should be on open circuit, otherwise current will flow backwards from the battery, through the cutout to earth at the dynamo. This will result in disaster if you leave it too long. Do a proper check of the voltage regulator.

Frank
F Camilleri

Also sounds to me like a sticking regulator cut-out but, Colyn, just curious, and before someone else asks you - what's that about using the regulator after fitting an alternator. Presume you didn't mean that? Or did I misunderstand you?
Bruce
Bruce Mayo

I was going to come back onto this thread to change a little of my hurried wording I used earlier to answer Judds question. My comment in brackets at the end would read better if I had advised you "to fit a battery isolator switch". Hope that helps.


Bruce, you are correct about the regulator, mine is now only used as a "connector block" for the wiring of my lucas alternator.
I followed the wiring instructions very carefully when I did the alternator conversion and the alternator worked perfectly. But I noticed that when I switched my ignition off, the engine stopped but the ign light stayed on even with the key out! Luckily I cut the power using my battery isolator switch and I heard the cut-out in the regulator click off which stopped an expensive short circuit through my brand new alternator.
Apparently, this happens on some alternator conversions and most people just use a separate connector block which isolates the regulator completely.
I took the easy (and reversible) option of using insulating shims of plastic between all the regulator points to prevent any further electrical contact.
This cured the problem and it has run fine for a few years now.

Sorry to take up so much of your thread Judd but your problem reminded me of my own experience.

If it is any help Judd I have a brand new voltage regulator which I bought but never fitted before my alternator conversion and you are welcome to have it. It is for a 1600 Mk I.
I will try find out what the postage is from here to the USA to see if that would be an economic option. Let me know if you want it and also let us know how you get on.

Colyn
Colyn Firth

I just replaced the Vreg. I manually checked the function of the relays and gapped them. Maybe I didnt clean the points well enough, could that cause the short? I will pull both the generator and the voltage reg this weekend and bench test and set them by the manual. I hope the genereator isnt torched.

BTW thanks for your help. U guys are the best.
Judd Irland

You were right. Cutout relay was stuck closed. Luckily I got to it in time and the genreator is still good. All is well again. Thanks.
Judd Irland

Thats great Judd, glad we were able to help.

Dont forget to fit a battery isolator switch when you can. Put it somewhere within easy reach, through the wooden boarding behind the seats is a popular location.
My battery isolator undoubtedly saved my car when I caused a dead short in the lighting circuit whilst connecting (incorrectly!) some new sidelights.
In the 30 seconds it took me to realise there was a problem and switch off, the front loom was burnt out and it cost me hundreds of pounds to get fixed.
The car would have been burnt out by the time I had managed to disconnect the battery.

Colyn
Colyn Firth

This thread was discussed between 24/03/2011 and 26/03/2011

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