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MG Midget and Sprite Technical - Dynamo or Regulator?

I used my midget 3 for probably the first time in the late evening with full lights on. The battery was fully charged. After about 12 miles car died with a flat battery. I have now charged battery, and get 12.7v across the terminals. Starting the engine, the ignition light goes out at tickover, but 12.7v drops to about 12.5v. Revs up to 4000 does not increase volts above the 12.5v level. What is likely to be faulty, regulator (RB340) or dynamo? I would be happy to replace either or both to get reliability but which one should I go for as most likely the cause?

Colin(whose not the best with sparky stuff)
C Martin

Change over to an alternator.
More reliable and more power
Onno K

First check is to test the dynamo.

Pull off the 2 wires ans link the terminals with a short length of wire.


Start the vehicle and let it idle. Fix one end of a 12v test lamp to earth and the other side to your linked wires. No need to rev the engine. The light should light brightly if the dynamo is ok.


If it passes this test, refit the wires and carry out the same test using the D and F wires at the regulator, this will test the wiring between the two.


Check the regulator has a good earth on the E terminal.


If that all checks out replace the regulator.


Or as has been suggested swap to an alternator.



Hope that helps.
SR Smith 1

Definitely get an alternator especially if you have any additional electrical items.
Jeremy Tickle

SR--Thank you very much for your help, dynamo OK, wiring to regulator OK, earth checks out OK, new regulator will soon be on order.
SR, Onno, Jeremy--- I know you are right re alternator but I have no additional items that I use and as said rarely use it in the dark. Any more probs and I will take your advice, but I do like the idea of originality.
Colin
C Martin

I too liked the "originality" of a dynamo. But when my regulator packed up it was considerably cheaper to replace the dynamo with and alternator rather than buy a new regulator.
Guy W

Glad that helped!



Good luck in getting a new RB340, there are so many c**p cheap pattern ones about now made in the far east.


Go for a decent make, Durite is a good company.



As Guy says often an alternator is a cheaper option in the long run.



SR Smith 1

Colin,

if you want originality but with modern reliability, have you considered one of these?
http://tinyurl.com/pz6ewpm you'll need to scroll down a bit to get to the dynamo-alternator. It's not cheap though especially as an alternator is under £40.


Jeremy Tickle

Hi Jeremy,


They seem a good idea, but...............



Fitted two and both failed within 6 months, one on a TR4 and one on an MGA.



Although that was a couple of years ago and hopefully they've improved.


Anyone else had experiences with them?
SR Smith 1

Hi all,
I have ordered a regulator from MGOC hopefully it will get me running quickly, I intend to look at/service the existing regular to maybe keep as a spare as I know modern stuff may be unreliable.
I also intend to fit a Sparkbright voltage monitor, this is an LED that changes colour and or flashes dependant on voltage that can be connected direct to the battery.
Having said all this I suspect an alternator will be fitted if I get any more problems.
Colin
C Martin

Hope that sorts the problem Colin.
Jeremy Tickle

I changed to an alternator, by using the Moss conversion kit.
The wipers now do more than one pass per minute, the lights shine and im sure the starter is spinning faster too. fitting the alternator is one of the better ideas I have had to be honest.
P Bentley

New regulator now fitted and back to charging. I will fit the SparkBright when it arrives, just to keep an eye on things. Thanks for all help and advice.
Colin
C Martin

Nice to hear you got this sorted.


SR Smith 1

SparkBright arrived and fitted. However, it appears to indicate overcharging at about 1800 rpm. When I checked the voltage at 2000rpm it reads over 16 volts.
Is this too high, am I boiling up the battery?

Colin
C Martin

Yes, that's a bit on the high side.

Your new regulator will need adjusting.

Dave O'Neill 2

Thanks Dave, that's what I thought. I don't think it needs adjusting by me. I think it needs sending back!
Not sure I even want another from MGOC. I should have taken SR's advice and I may now do it.

Colin
C Martin

I'm not sure about the quality of modern replacement regulators, but I would imagine that an original Lucas wouldn't necessarily have been set correctly straight out of the box.

There must be variables for individual dynamos, so it would be difficult to factory set.
Dave O'Neill 2

IIRC there are instructions on adjusting the voltage regulator in the workshop manual. Twas a routine job back in the day...
David Smith

Hi again,



Sorry to hear that you're still having problems! 16 volts at the battery is way too high.



A control box should not need adjusting, it ought to have been factory set up.


The quality of these units is very suspect in my experience, I had 6 for a P4 Rover once before we got one that worked once.


If you're not concerned about originality go for an alternator conversion.


Regards Steve.
SR Smith 1

"IIRC there are instructions on adjusting the voltage regulator in the workshop manual"

There are even instructions for setting it a little higher, for cars doing a lot of short trips etc.
Dave O'Neill 2

My opinion, and MCOC,s is it should work straight out of the box. Its on its way back for an agreed refund and a Durite one is on its way. Proved the use of the SparkBright is useful as that was first indication of over charging. I suspect an alternator is getting closer!

Colin
C Martin

This thread was discussed between 23/05/2015 and 13/06/2015

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