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MG Midget and Sprite Technical - Over charging & jumping out of first

Hi

I've been across to the Lake District this weekend and on returning home I went to start the car to put it in the garage and the battery was completely flat, it wouldn't even light a test bulb. On further examination the battery was quite hot. Any suggestions, has it overcharged and cooked the battery, how can I test the battery and the voltage regulator or do I take it to an auto electrician? Incidentally I am still running a dynamo.

Secondly whilst climbing Hardnott and Wrynose passes it jumped out of first gear on a number of occasions. It is on a relatively new ribcase which has covered approx. 5000 miles. For those who don't know this road, it has some sections which are possibly 1 in 3 gradiants. Is this a known problem and is it an easy fix? Thanks.

John
John Stephens

Hi mate

John it is not uncommon for the battery to be damaged by too much charging.This happens when the voltage regulator becomes faulty and allows the dynamo to charge at more than 19Volts depending upon RPM of the engine. Occassionally this will melt the solder on the commutator of the dynamo and damage that also. Thus you can end up with a stuffed battery, Voltage reg and dynamo.

First thing you need to do is fill the battery with distilled water (If it is down) or get a new battery. Then with engine running measure the voltage across the battery. If it is substantially more than 14.5 volts when the engine is reved then get a new regulator from an auto electric place, or try to set your old one up (often easier to simply replace they are very cheap when purchased locally)

If on the other hand you have no charge then you have a good chance of a damaged dynamo

See here http://www.midgetregister.com/
then select "workshop" and "Charging system", should contain all you need to know.
Robert (Bob) Midget Turbo

NEVER EVER just fit a regulator and think it will be fine

ALWAYS have your regulator setup by a good autospark

The most common cause of charging problems can be eliminated by fitting a properly set regulator, should leave you without any under/over charging issues for years to come.
PeterJMoore

John, as Peter says, take your Dynamo AND Regulator box to a good 'old school' Autoelectrician who knows how to set up a regulator to your own dynamo....

As for the box jumping out of first, climbing a 1 in 3 (and it wouldn't be driven with a light throttle would it.... lol). Possibly the detent spring for fisrt / second selector may be weak...?

Mark.
M T Boldry

Can't agree with that Peter or Mark. After reading your posts I tried to think back over the last 40 years I have had vehicle with Dyanamo charging systems. In that time I have bough if I remember correctly about 5 new regulators NONE of which were faulty and all were set up perfect, as they are designed to be. Naturally I would always check the output of the system when installed by use of a meter across the battery. :)
Bob Turbo Midget England

Well Bob, that's just luck. Every car, dynamo, regulator will be different and as such the regulators should be set specifically for your car.

You do agree to an extent as you have checked every charging system when you have fitted a regulator. That in itself shows your faith in parts off the shelf ;)
PeterJMoore

Hi Pete.
Why should they all be different? They are designed to be used with the 22amp dynamo and the RB 106 and RB340 will as a result be set for 22amps, in fact if my memory serves me correctly the back of the RB340 is stamped 22amp?. There were some special (high)output dynamos about over the years but these were rare and were very rarely fitted to road cars.
IMO unless your car has a very large dynamo installed on it then it is safe to assume that a new regulator will be supplied set up correctly to suit your dynamo. However with all things new it could be faulty and should therefore be checked when installed for correct charging simply with a meter. If you take the view that everytime you install a new regulator that you have it set up by a competent autoelectrician then why bother faultfinding in the first place? simply take your car to them and let them sort it for whatever price they charge.
Bob Turbo Midget England

I do agree with most of what you say there bob, however, as with any mechanical parts, they degrade/vary with use. As such I would not expect a 40 year old dynamo to produce the same results as a recon/rebuilt one.

Brushes wear, dirt builds up, cables become brittle and their resistance goes up, etc etc.

On top of that a local "old school" guy who used to own one of the largest electrical reconditioning businesses around advised us to ensure we had the regulator setup on every car we do to at least try and eliminate future problems arising from over/under charging.

PeterJMoore

I had a ribcase that used to jump out of first gear so I had it rebuilt. When I got it back and fitted it I was not pleased to find it still jumped out of 1st. I had it exchanged for another box that never gave me any trouble.

So, if it jumps out of 1st after 5000 miles it wasn't properly rebuilt - just had new bearings or whatever. Take it back.
Daniel Thirteen-Twelve

The regulators are adjustable, which suggests that someone on the assembly line where they are put together has the job of adjusting the screws until it is within the design limits and ready for despatch.

The job must be rather tedious and no doubt they have their off days. I would imagine that the occasional one must be set wrong - or at least towards the limits of tolerance so if you know what you are doing it must be sensible to check, just to be on the safe side. But not being very confident with electrics myself, I would probably just fit and hope it was right.
Guy Weller

John,

Regulators are usually set up correctly, I used to run a Lucas /CAV repair workshop and never found one wrong, except a couple of old stock where the points were a bit corroded.I expect what has happened is the cut out points have stuck closed and the battery has been trying to turn the generator, ie turn it into a motor that why it was hot. How long did you leave the car between getting home and trying to put it away? Exchange dynamo and regulator required remeber to flash first to get the polarity right.

Mike
M J Pearson

Cheers all and thanks for all the info, I'll get stuck in this weekend when I've priced it all up! I think I've found the right Autoelectrician if I need him. An excellent website Bob, thanks.

Mike, an interesting explanation, I guess it was probably about 45 minutes by the time I was ready to put it away.

Mark, good to hear from you, are you all settled in? I guess you could be right about 1 in 3's and a heavy right foot!! However next time I have the engine out I'll have a look, what's involved if it is a weak spring, is it a full strip down or something reasonably simple to do?

John
John Stephens

Why (unless you have a concours example) don't you chuck all that old rubbish away and fit a alternator? you could then run headlights/ indicators / etc. that work!
d cusworth

Well guys I fitted a new battery today and used a multimeter to measure the voltage across the battery which at fast idle was just under 14 volts and at high revs 14.3 volts. haven't driven any distance yet but hoping it was just the old battery giving up the ghost!! In any case I'll get it checked out.

d c It's a frog and I'd like to keep the original rev counter driven off the back of the dynamo.

John
John Stephens

Well done John you may have solved the problem.

Just for a few days keep checking the output to make sure that you don't have an intermitent fault.
Robert (Bob) Midget Turbo

John, that's a perfect reason to keep a dynamo! I hope you have cured your problem.
d cusworth

This thread was discussed between 16/05/2010 and 20/05/2010

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