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MG Midget and Sprite Technical - Dynamo to Alternator Conversion

Hello,

I'm in the process of restoring my father's '71 midget and am converting the old failed dynamo to an alternator.

I've been scouring the internet for the wiring instructions and the few pages I've found have been either for different cars altogether, not clear or contradictory.

Could anyone please help me with either the instructions and diagrams or a good link which would apply to this car & year.

Many thanks from a despairing individual!

Duncan.
D J Ross

Many people and companies make this a very complicated job when in fact it is extremely easy.
When fitted the alternator has 3 connections. The 2 larger connections are joined together and fit to the live connection from the battery, generally at the starter solenoid although it is irrelevent exactly where. The alternator is earthed through its metal chassis and the only other connection is from the small terminal on the alternator. This wires to one side of the ignition warning lamp. The other side of the ignition warning lamp is wired to the terminal on the ignition switch which is live when the ignition is switched on. Wired like this and everything will work fine. When you read other ways of doing this it is simply picking up these connections using existing wiring. You can then simply remove the voltage regulator (control box) and all its connections and job done.
Bob (Robert) Midget Turbo

Bob,

"and all its connections" Thats the trick. Most of them can be joined with one big blob of solder tin but the earth has to be separated as wel as 1 other wire IIRC. But Duncan if you try the search option on the archives you'll find tons of info on this subject.

Did the conversion years ago and its one of the better mods that can be done but change to neg earth and remove the control box too. If you choose the right Alternator you'll be facing a raise in charging power from app. 20 amps to more then 40 Amps. That does a lot for our cars. At least you wont have to choose between wipers, headlamps and blower when its dark and raining:-)
Bas Timmermans

As Bob (and Bas) says this is a very easy mod

you need to be fitting it to a negative earth car

(changing if positive earth is as easy as following the diagram)

If you want the car to look standard (IMO old fashioned) you can leave the control box in situ and take the WL wire to the small terminal on the alternator

or as Bob says take the feed direct off the ignition switch to the small terminal

the large terminals (if you use a standard Lucas type alternator) both feed the battery, via the starter solenoid connection (for convenience), when the alternator is turning under power.

The diagram shows the wiring for leaving the c/box in place, I did the Bob method and removed the c/box and its unused wires

for some barmy reason the sketch has come out half sized but you can probably see what we mean

hth


Bill

Then again, it may only be worn brushes in the dynamo. It is very easy and inexpensive to replace them. I have found that the generator in my 1971 lasts about 80,000 miles between brush service.

Last year, the bushing in the rear of the generator of my car finally wore out. I replaced it with a new dynamo made in India. This one puts out enough current that the generator light no longer glows at idle. I kind of miss that as the slightly glowing light indicated a proper idle speed setting.

Maybe the problem in your car is the voltage control box?
Glenn Mallory

I'm sure someone will correct me but while you're at it, swap the leads on the coil too as although it seems to work fine whichever way round it's wired, that's the only reason that I can see why my petronix electronic ignition module got fried when I installed it (after mine had been converted from pos to neg by the previous owner/builder).
G Lazarus

AS DJ says, with simultaneous change to -ve earth, the coil connections will need swapping. +ve to white ign lead; -ve to dissy white/black.

This is so the spark jumps from the central electrode (which is coated to assist with electron emission, in the similar manner to a valve, to create the cloud of electrons ready to form a plasma when the spark is initiated) rather then from the inert outer electrode to the inner.

The only other comment I have is: the field winding (from dyno to box) may be joined to the ign warning light wire at the box; simplifies the wiring, IMO.

A
Anthony Cutler

Hello Duncan,
Here is a link to lots of good info on alternator conversion: http://mgaguru.com/mgtech/electric/electr_2.htm.
Although I'm in the midst of my first British resto
('65 Sprite) I have converted several old 50's vehicles to alternators over the years and it is quite easy.
Good Luck
Bob Davis
R.W. Davis

This thread was discussed between 23/11/2008 and 25/11/2008

MG Midget and Sprite Technical index

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