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MG Midget and Sprite Technical - Regulator Problems?

Having driven for a couple of years with an ammeter fitted to my Frog, I have just replaced the ammeter with a voltmeter. I have never had any obvious charging problems over the last couple of years.

I now find myself watching the voltmeter as it indicates a climbing output voltage! On start it registers around 15v very roughly. As the engine speeds up, the output goes up, so as I trundle down the road at say 3000 rpm it is indicating about 15.5 (the divisions are rather course and I am not sure what voltage the line to the right of 15V indicates).
As I carry on driving (same rpm!) the output climbs so that after about 10/15 miles it is pretty well full scale.

When I returned I made some checks. The battery is 13.2v (engine not running) and I am registering about 17V with the engine running at 3000rpm. If I turn on headlights the indicated voltage drops back.

I would have expected the charging voltage to drop off after a few miles. Is what I am seeing "normal" or do I have regulator issues?
Graeme Williams

I think I'd remove the gauge and 'carry on!' myself ;)

I don't think mechanical regulators are quite as precise as they used to tell us

Maybe watch the electrolyte level in your battery (if you can actually get in to look at it) but otherwise don't fret
Bill sdgpM

THat was my thought Bill, but the output was getting higher and higher. I thought I might bend the needle on the gauge!

I thought I might overheat the battery or do damage to the dynamo if I leave it.
Graeme Williams

Are you making the checks with the fitted VM or using an external one to compare it?

I know from experience that the reg CAN pack up suddenly but it is fairly rare unless there is also a problem building within the dynamo

(of course if you take the thing off you won't get a bent needle) ;)

Sorry but ...
Bill sdgpM

The regulator indeed if your voltmeter is correct, which I suppose it is, as it reads 13,2 after charging. 17 is too much!
Flip. It can blow your dynamo on long runs. The original workshop manual is very instructive about how to regulate the regulator.
Flip
Flip Brühl

I have crossed checked with a separate volt meter which backs up the "Smiths" gauge.
I don't think it's a new issue Bill, just I would not have known with the ammeter. That just showed a nice charge going in! Not suprised with 17v behind it.
I'm concerned the way the voltage increased over a 20 mile run. I wonder whether that was because everything was warming up.
Graeme Williams

Or convert to an alternator. Bad Boy Classics sell an alternator that is camouflaged as a dynamo. With revcounter takeoff for Frogeye as per C39 Dynamo. They are about £135. Graeme - JC has about 3K miles on his now.
Alan
Alan Anstead

This emphasises why I wouldn't contemplate having an ammeter fitted

Tells you its all on the up (or down) without telling you what UP is

I think you could try altering the output in accordance with Nigel's book (Or most Haynes's for dynamo cars to be honest) or take Alan's advice and get a sleeper alternator which doesn't look it

I fitted an alternator to Lara as a matter of course when I was building her up, using a Mini alternator bracket for the A series

Not necessarily a cheap option, I had two pack up before the nice AA man fitted me this one when I was heading south to Le Mans one year a while back
Bill sdgpM

I was expecting you to advocate an electronic control box Alan!
Reading the setting procedure in the manual (thanks Flip!) it doesn't seem too complex so I will give it a try before Saturday so that if I decide enough is enough I must get a discounted purchase at the Show.
Now, where's my hammer?
Graeme Williams

Had a go at the regulator. The voltage, when I followed the procedure in the manual was creeping up to 17.5! Reset to 15.9/16.0 at 2000 rpm so I will see how it fares on the road.
On the voltmeter it reads just over 13 but presumably that's because there is now a load connected.
Graeme Williams

So glad I purchased a decent multimeter! It is becoming indispensable, even down to checking the freezer temperature (it was 4.2Volts!).

THe only minor issue was I note that the Manual uses a moving coil meter - probably all there was in '58. This would damp out minor fluctuations and record the
"steady" reading as noted in the manual, whereas a digital meter tends to waver a bit.
Graeme Williams

The old regulators are better than the new ones who deregulate over time. I lost 2 dynamos because of a new regulator. So I changed to an cheap alternator.
Flip


Flip Brühl

I've no idea hold old this one is. It looks old.
My main concern now (which I have yet to test on the road) is whether the output voltage is going to increase with time. I don't know why that should be although I see in the specs that the voltage is temperature related. But not to the extent that I was seeing.
Graeme Williams

Is it the right time to mention an electronic control box?
Alan
Alan Anstead

there's a rumour...
Bill sdgpM

Is a suitable electronic control box made or available in the UK?
Colin
C Martin

http://www.dynamoregulatorconversions.com/
d brenchley

As an electronic control box is a similar price to one of the fancy alternator/dynamo-with-tachodrive I think the latter would be the better option but I'm not giving in yet.THe charging voltage responded to the twiddling of the appropriate screw so that's a good sign!
Graeme Williams

It seems that I've seen some DIY articles on converting regulator boxes to solid state electronics.
Trevor Jessie

I agree with Graeme, they seem a bit expensive, I think a bit of adjustment may be the answer to my overcharging as a first off!
Colin
C Martin

This thread was discussed between 03/03/2016 and 04/03/2016

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