C10 charging / dynamo

[Rick Rybicki]

Well, done about 90 local miles on barn find. Running as expected.
Yesterday it let me down. My fault, a connection I'd made came adrift and shorted out causing the 20 amp fuse in my new wiring harness to blow.
Fixed the fault, put in new fuse, all working well......except it's no longer charging the battery.
CVC was professionally rebuilt and was working.
The dynamo is no longer showing any significant output. 0.3 to 0.5 volts when engine is reved.
Question.....could the short circuit and subsequent blown fuse have de-magnetised the dynamo?
All was working fine before the short circuit and everything is working fine except the lack of charge.
Help please. Thanks, Rick.

[Rick Rybicki]

OK....That seemed to baffle you lot!   Here's the follow up... Flashed the dynamo.
Checked the dynamo output again....Got a reading of about 7v at tick over. Reconnected dynamo, started engine, ameter showed discharge and ignition light remained on.
Tried a different (working) CVC. Ameter still showing discharge and ignition light remained on.
Flashed dynamo again, tested it with engine running, showed a reading of up to 10v.
Reconnected dynamo, started engine, great! ameter showing a good charge, ignition light off.......for about 10 seconds then back to discharge and ignition light back on.
Checked dynamo again.........no output.
HELP! Is it time to go and see the dynamo man?

[Group Leader]

I presume it's a Lucas dynamo of some description? 

This might help:

https://matchlessclueless.com/electrical/lucas/testing-lucas-dynamo/

Looks like the field coil is past it's best.   Field coils can be purchased  (about £15 if I remember correctly) but are slightly difficult to fit because the pole piece has to be in really intimate contact with the case.  This is achieved by doing the mounting screw(s) up extra tight using a lever screwdriver (slightly tricky unkess you happen to have one) plus you need a pole expander which I believe is used to stop the casing collapsing when you are pressing down hard to do the screws up.  Again tricky unless you have one or can conjure up an adequate alternative.

http://classicrider.dk/dokuments/Lucas/1953%20Lucas%20Dynamos%20E3L%20E3LM%20E3N[2].pdf

The simple test of disconnecting the dynamo completely,  linking the F & D terminals with a 6V bulb to ground is good to establish that the dynamo is/isn't working without the concern of wiring, regulators etc etc getting in the way.   When investigating my new acquisition B21 the other day I did just this as it has incomplete wiring and the regulator and battery are missing.   Don't rev the engine excessively when doing this test though.   I'll be using a DVR2 electronic regulator onthe B21 that can hide in an original housing but has the advantage of being a very good regulator compared to the crude mechanical ones originally fitted to most biles and cars of the age (how on earth did they ever keep going for so long?)

As to the cause of the problem being the short circuit; it probably depends on what exactly was shorted to where!

Hope that helps.

Alan

[Rick Rybicki]

Hi Alan, Thanks for that. Yes it is an old Lucas. Not sure of model as it's still on the bike and I can't see the numbers. It's the early type with the cover band with the external nut and bolt clamp. The bike is 1946. I've used the "Clueless" site and it's very helpful.

I think I've now come to the conclusion that it's time to take it off and put it in the hands of someone who knows what they are doing, probably "Carwood" windings in Yeovil. They re-conned my Voltage Regulator.

I think I have been dealing with two separate problems that occured at a similar time. The short circuit happened in the headlight dish when the pilot light connection came apart. Blew the 20 amp inline fuse in the pos+ lead from the battery.  Unlikely to affect the dynamo I think.
As the bike has been "standing" for about 50 years and is "unrestored" apart from a new wiring harness, just the fact of running it again may have brought about some age-related fault in the dynamo that wasn't initially apparent. I did flash the dynamo when I first got the bike going and it was charging fine. I have been using the bike and It's done about 90 miles since I got it back on the road.

Still don't understand why it started charging for a good 10 seconds then stopped again.
Anyway, it's coming off and going to an expert.
Cheers, Rick.

[Group Leader]

When I got  my AJ a couple of years ago I managed to coax the dynamo back into life but it was only short lived.   In my case some of the armature windings were open circuit so I purchased a replacement.   The replacement was fine except that the diameter for the main bearing was a couple of thou over size which impeeded re-assembly.  What I should of done was skim the diameter down to the correct fit with the bearing.  What I did do was to just struggle to re-assemble it which later led to other issues but that's another story.   

Still, it's all working well and I now know a lot more about the old Lucas dynamos than I did.  As I new nothing before that may or may not mean much!

Every day is a school day as they say.

Alan