Dynator trouble shooting

[John L]

I hope I can ask this on here, I'm helping a friend with an MG TD, that he thinks has a Dynator instead of the old dynamo, looks just the same. The red warning light comes on at times, and does go off again, we havent put a voltmeter on it yet, so wanted to try and get some info before mucking this up.  It does have an old style black control box, I looked inside, it doesn't have the usual 2 coils, it just has a small printed circuit board, so didn't want to do anything just yet until I know what to check.

I think it should be the same sort of unit that could be fitted on TR's perhaps.

Any info would be greatly received.

John

[RobH]

Are there any markings on the 'dynator' unit John ?   Most of them seem to use a Denso alternator with internal regulator - it's unusual to have a separate one in the control box if that's what it is.  

Does the generator have an all-metal body and a take-off at the rear for the tacho drive, or does it have a  plastic body with alloy end-caps and no drive take-off? 

 

 

[John L]

Its a black body with ali endcaps and a tacho drive on the end, I'll give it a closer look for any markings,  it just has 2 wires at the rear, a large and and a small, just like a dynamo.  Could it still be a dynamo with that sort of control box, I've seen others with a large fuse across 2 terminals inside.

John

[RobH]

It could be a Dynalite then: 

https://www.powerlite-units.com/dynalites/rac006t.html

It's also possible it is a still dynamo and the control unit has been changed for an electronics type. 

https://www.dynamoregulator.com/products.html

[John L]

I've had another look at this today, inside the regulator is a USA address, for a solid state voltage regulator,  so it would seem that it is still a dynamo, the red light is now on all the time with the key on, even reving the engine and there appears to be no output from the large wire with a volt meter.

 Do I now assume that it could be a brush problem? Do I follow the old Lucas tests for a dynamo?

Thank you Rob for your wisdom, sorry I wasnt correct in the first instance, the guy hasnt had the car that long, and was told that it did have a alternator fitted, but I think this box now confirms its not an alternator, I found this website and address matches the label in the control box.  https://mgaguru.com/mgtech/electric/et232.htm

Thanks again,   John

[RobH]

Yes standard tests for a Dynamo John but of course you can't follow the control box bit.  If you disconnect the dynamo and connect the small and large tags together, there should be a large voltage there when the dynamo is rotating. If not suspect brushes or a worn commutator. 

If there is a considerable voltage ( up to 20 v or more) the dynamo itself is OK and it might be that control unit has failed.