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MG Midget and Sprite Technical - MK1 dynamo connections

Just connecting, and double checking that I have the dynamo and regulator connections correct. Re-reading J E Davies' "in defence of dynamos" articles in the MASC magazine has got me nervous about getting it all wrong!

Firstly the colour coding in the MK1 and the MK2 workshop manual diagramms (facsimilie copies) changes. Then the colours on a photo in one of the MASC articles doesn't quite match either. The critical wire is from the F terminal on the regulator, to one of two termnals on the dynamo. The earlier workshop manual doesn't label these, but the MK2 one shows it going to the F terminal on the dynamo, which would make sense. F goes to F.

But, which is the F terminal on the dynamo? I cannot see any marks on mine! I am guessing its the smaller, upper one in my photo but guessing isn't good enough for this!





GuyW

Guy

The F terminal is the smaller 2 BA one
Bob Beaumont

Thanks Bob. I thought it probably was, but without markings on the dynamo I couldn't be absolutely certain!
GuyW

Guy, I think the F stands for Field. Anyway that's how mine has always been wired and it works ok! I see yours has the correct fibre insulator plate between the terminals, Mine has broken, have you any in your collection of bits??
Bob Beaumont

Sorry, no Bob. No spares for these. I bought the dynamo from John Davies, together with the regulator, so he would have checked it came with the insulating spacer. Though it looks more like plastic than fibre. It may be that John made one to fit!
GuyW

John Davies has came up trumps again!
Bob Beaumont

F is "field". The regulator, in effect, connects and disconnects it continuously and rapidly in order to regulate dynamo output, something like the electronic regulator in an alternator.
Bill Bretherton

Still a mystery to me Bill. All the fields round here have cows in them. Or sheep.

But, just to be certain, the F terminal on the dynamo connects to the F terminal on the regulator? And the other, fatter wire, is the "pipe" that the generated electricity flows out of the dynamo along?
GuyW

LOL guy! Yes, that's as I understand it. The field winding is "exciting" the armature via a magnetic field. When excited the armature generates an emf (voltage) which drives a current down the "pipe" via the D connection. However, the armature, if left unfettered, gets too excited and produces too much voltage so the field is continuously "collapsed" (via the regulator) to reduce the voltage down again and so on. So it's important the regulator is working correctly (a dynamo output voltage check will verify that). The regulator also disconnects the dynamo from the battery when voltage is insufficient to charge it i.e. at engine idle.
Bill Bretherton

Ok, I think I understand the principle, if not how it actually achieves this.
One thing I am very confident of is that the dynamo and regulator are set up precisely and accurately as they were done for me by J E Davies, and supplied as a matched pair. All I need to do for my part is to make sure that I connect it with the right wires to the right terminals!
GuyW

Guy, sorry if that was too much information! In my Frogeye workshop manual wiring diagram, dynamo D terminal (larger) connects to D on regulator via yellow wire. Dynamo F terminal (smaller) connects to F on regulator via yellow/green wire. The wiring diagram doesn't actually identify the dynamo terminals but they can't be anything else as confirmed by Bob.
Bill Bretherton

By the way, it sounds like the regulator will have been checked and adjusted if needed, which is reassuring as it is very important for correct operation. I'd still check the charging voltage at the earliest opportunity though, which I'm sure you'll do.
Bill Bretherton

Never actually occured to me that the letters F, D and E on the regulator stood for Field, Dynamo and Earth. I thought they were just alphabet letters that might come after A, B and C somewhere else.
It does make connecting the regulator up a bit more obvious!

A and A1 are, to me, a bit more obscure other than I realise they are the power connections from battery (why not B?) and to the fuse box and ignition/lighting switch. - the latter connects to a terminal on the lighting switch which is also marked A, which now I know the code, is quite pleasing.
GuyW

A is for "ammeter" as I think it was the intention that cars would/might have an ammeter in the past. For some reason Spridgets weren't fitted with them so the "A" terminal goes to the battery directly (which the ammeter would anyway). A1 is an "extension" of A to indicate accessories (the "A" not necessarily being the A in "accessories"). Some regulators have an A2 and A3 as well. It's just old Lucas nomenclature.

If you have a spare Lockdown rainy afternoon Guy, this Lucas article tells you all you need to know:

https://www.mg-cars.org.uk/imgytr/pdf/lucascourse5.pdf
Bill Bretherton

Guy,
might you read that as it's a suitably old technical publication (not a more basic book obviously).

As on this occasion you don't want to learn for yourself by intuition, instinct or experimenting I offer this audio visual lesson for rejection but others might like it. :)

https://www.youtube.com/watch?v=KL5ioH8idFI


Nigel Atkins

This thread was discussed between 07/05/2020 and 08/05/2020

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