I just need a bit of advice.
I'm testing and re-furbishing the dynamo on my WM20. I've checked the field windings and am getting a resistance of about 3 ohms and I tried to test the armature windings but this registered as open circuit. I think I've discovered the cause of this; both brushes worn out and one seized into its holder. I'm assuming this is relevant because I assume that the resistance testing is carried out through the brushes.
So...I've got a new pair of brushes on order but am I right in thinking that I can also test the armature resistance by touching my ammeter probes on adjacent commutator segments? If so then the reading I'm getting of less than 1 ohm, seems to suggest that the armature is also ok as it's supposed to be 0.6 ohms I believe.
Can anybody confirm that I'm on the right track here?

Brooky.

email (option): chasgbrook@hotmail.com

Just join the D&F wires together and put a battery across them and earth. It should motor. If so you have a good chance that it will work but not always.Make sure it motors in the right direction. Then spin it up in the right direction with a fast drill and see what volts come up.

Thanks Douglas but I can't do that with the dynamo in place on the engine.
The measurements I've got are 3.2 ohms through the field windings and 0.6 ohms through the armature windings. I initially got an open circuit reading when testing the armature windings. The cause of this was traced to one of the brushes being seized solid into its holder and which had subsequently worn away until it no longer made any contact, so that reading was taken by attaching the meter probes onto diametrically opposed commutator segments; not easy to do with the dynamo assembled and on the bike! I confirmed the validity of this test with an electrician at work today, so I'm happy it's ok.
This all augers well for when the new brushes are fitted. Should work fine!

Brooky.

email (option): chasgbrook@hotmail.com

Hi Brooky,

You can try reading "Testing a Lucas dynamo"
On http://matchlessclueless.com/electrical/lucas/testing-lucas-dynamo/

Or

http://www.vicus.org.uk/johnash/dynamos.htm


Regards,
Noam.

email (option): noam10@gmail.com

Hi Noam,
Yep, I've read both of those but neither makes mention of testing the armature windings via the commutator segments but, as the commutator segments are connected to the armature windings, it must be a sound means of testing the windings. I think I've convinced myself that it's all ok and has tested fine.

Brooky.

email (option): chasgbrook@hotmail.com

Hi Brooky,

According to this Lucas PDF-
http://classicrider.dk/dokuments/Lucas/1953%20Lucas%20Dynamos%20E3L%20E3LM%20E3N[2].pdf


Your field resistance should be 2.8 Ohm,

And here:

http://www.voc.uk.com/net/docs/16/16-320-37.pdf

I fond that on E3L (Same as "M")-

Armature resistance (Brush to brush) is 0.55 Ohm.
(Of course you would like to check it between each pair of the commutator)

But if you want to bench test it as a motor,
It only takes unbolting 1 bolt and release the metal strap to take it out.
2 min of work..

Best regards,
Noam.

email (option): noam10@gmail.com