Charging Diagnostics

[RupertW]

Hello all, 

I'm hoping for some advice on the charging system on my Chummy project which I'm now not able to get charging. 

I've previously had everything wired up and charging correctly, and the dynamo has been refurbished. I had the wiring removed to work on various bits since then, and having now wired it all up as it was previously it is not showing any signs of charging, so I'm trying to work through the system methodically, starting with the Dynamo. 

I know there's a lot of information on charging systems already out there, but I've managed to get fairly confused by it all. Is any able to explain in very basic terms how to test if my dynamo is charging, preferably without removing it from the car. I have both a digital and an analogue multimeter. 

Below hopefully is a picture of the top of my dynamo showing what I'm working with:
   

First question, is how do I identify which terminal is SH, and which is D? 

And the second question is what/where do I need to bridge in order to see if it's charging? The car is negative earth, so do I just put the multi meter between each terminal and the battery's negative earth post in turn to see if there's an output for each circuit? 

Apologies if these are basic questions, but any help would be much appreciated!

[Dave Mann]

    The left hand terminal is D or Pos and the right hand terminal is SH or F1. Link the two terminals together and connect your meter between either terminal and a good earth, the dynamo case and run the engine being aware of the proximity of the fan.

[RupertW]

Thank you, that's very helpful - I hadn't noticed the terminal marks on the cover.

I've had an attempt with terminals linked and both multimeters but annoyingly both multimeters seem to be malfunctioning so I can't get any clear readings. I've tested both on a seperate 12v battery and they're all over the place, so fairly sure it's not electrical interference and my fault for buying cheap equipment. They did seem to give some sort of reading when revved up but a bit all over the place. I'll see if I can dig out a 12v bulb from somewhere and see if I can test things the more old fashioned way.

[Stuart Giles]

I've had an attempt with terminals linked and both multimeters but annoyingly both multimeters seem to be malfunctioning so I can't get any clear readings.

Are they Digital meters with LED/LCD readouts? They aren't any good for testing changing voltage/current as the dispay will change too fast to get a reading. An analogue meter, i.e. one with a needle display should give you good idea of the dynamo output.

[RupertW]

I have both a digital one and a very cheap analogue one with a needle, and neither of them seem to be any good!

---

I have ended up taking the dynamo off the car and put it on the bench as I wasn't having any luck. 

With the terminals bridged and a a positive lead directly to the battery, and a negative to the body, it does motor. 

It only seems to be turning at what I'd estimate to be a few hundred RPM. Is that about what you'd expect from a healthy dynamo or should it be turning with a fair bit of speed?

[Tiger]

Best to check the output
You can use a standard drill to turn the shaft(make sure it’s the correct rotation)
When I had a similar problem turned out to be brushes
Use a 12/6 volt bulb
Regards
Tim

[RupertW]

I've tried it with the drill, but my voltage readings are very low, about 0.5 volts at what I'd approximate to be about 1500 rpm. It isn't lighting up any bulbs.

I've cleaned the commutator which was a bit grubby, but otherwise to my untrained eye I can't see anything obviously wrong and there's no smell of burnt electrics or anything.

I'm a bit confused that it would motor quite happily but isn't showing any significant output. As the car didn't go anywhere for a year or so is it possible that it's lost some magnetism? I could increase the spinning speed or try measuring for longer in case it wakes up, but I don't want to damage anything by running it disconnected.

[Tiger]

I think if it’s not worked for some time it would need polarising.
Lots of advice on the forum.
By the way whereabouts are you ?

[RupertW]

Success!

Turned the drill up to a higher setting, spun it for a bit longer, and there was suddenly significantly more resistance and a good strong current being produced as verified by both the multimeter and the bulb.

I'm pleased as I had splashed out on a reconditioned dynamo and was worried it had already gone wrong. The engine has had a nasty clatter that wasn't there before, so I'm hoping the dynamo having more resistance might sort that too.

Thanks all for the pointers