dynamo on strike

[bsa-bill]

gave the Flash a look at the outside world yesterday, this bike will be for sale shortly so having got my new shed fettled and my original bike shed fettled my intention was to give the Flash a run to se all was well before taking some pics and moving it to the original bike shed, not to be, I switched lights on full and checked the ammeter, damn no charge, it had been working fine as little as a month ago maybe so spent a couple of hours today checking the dynamo leads for continuity, yep fine so next check dynamo output  I got 0.6 volts.
Working on the dynamo in situ and stop starting the engine bike in the shed is asking for burnt fingers hand so quite a few breaks now and then so took a while checking brushes, wires making contact the usual things with no joy so gave up till tomorrow, then after reconnecting the DVR I gave it one more kick, rev up checked the ammeter and low and behold lights on and a balanced charge.
So  I'm wondering could it be lack of magnetic field which then sorted itself, I'll check again tomorrow, any suggestions
               

[morris]

I’d put my money on a bad contact/earthing somewhere, or one of the brushes stuck in it’s holder.
Did you try repolarising? If the bike hasn’t ran for quite some time, the dynamo may have lost it’s polarisation.
Another possibility is that the field coil has a breakage somewhere in it’s wiring which closes up when the dynamo gets hotter.

[RichardL]

Because it worked after reconnecting the DVR,  an intermittant wire termination, or terminal, at the DVR is a candidate.

Richard L.

[bsa-bill]

Thanks for the reply guys.
After todays chores grass cutting (batteries went down), resetting the mouse traps in the garage (1 kill) I had time for quick look at the Flash, started with the bad connection possibility, both wires from the dynamo had checked out good for continuity so took them out of the Dynamo once again, never liked that connector on the dynamo and had a slight suspicion the green wire was a bit slack, however with the benefit of a spotlight this time it turns out it is pretty firm when pushed in, the yellow lead not so much, it should be in contact when the keeper is crewed up but it definitely is not tight when just pushed in, pinching the socket thing a bit tighter was a thought but could lead to a much bigger job, so tomorrow I think I'll give the bullet a coat of solder to create a snugger fit. then try it all again.
Richard there was no output from the dynamo tested across the dynamo leads (not contacted to anything) so it's dynamo related

[Bsareg]

The brass "bullets" in the dynamo end are usually split which enables you to spread them a little if slack. Are you sure no one has fitted the narrower standard bullets ?

[bsa-bill]

Thanks for the reply Bsareg  - the bullets on mine are soldered on , I know what you mean by the split ones, mine are  the ones in the pic never been a problem before and I've had the bike since 1999, quite possible it's been intermittent and with a full battery I've just not picked it up, but one of them is not a firm fit, I think cutting them off and putting on the split ones might be the way to go but first I'll try a run of solder down one side of the bullet and see if it tightens it up.

[groily]

It isn't that rare for a dynamo to need a handful of revs to kick in after lying dormant for a bit, as the remanent magnetism may simply have dropped off as you suggest. Some are better at retaining it than others (one of my three is noticeably more reluctant to fire up than the other two, all with DVR2s fitted).
Frequent use avoids the problem, but hibernation for a month at a time, say, aggravates it.

[bsa-bill]

It isn't that rare for a dynamo to need a handful of revs to kick in after lying dormant for a bit

Thanks Bill, I had not heard that (more likely I had and had forgotten) and on reflection you could be on the money, however as I've got the end cap off I'll fix the wrong bullet issue, I'll try a run of solder down the length of the bullet.

thanks all for useful replies - Bill

[bsa-bill]

got a minute or two yesterday so plugged the solder iron in and put a good layer of solder around he slack nipple, had to file it down a bit to get a snug it, switched the lights on full and gave the Flash a kick, first kick start and the ammeter needle flicked about a bit and then settled nicely in the middle - result
Thanks for the input chaps

[KiwiGF]

got a minute or two yesterday so plugged the solder iron in and put a good layer of solder around he slack nipple, had to file it down a bit to get a snug it, switched the lights on full and gave the Flash a kick, first kick start and the ammeter needle flicked about a bit and then settled nicely in the middle - result
Thanks for the input chaps

Most likely brushes in combination with a reduced residual magnetism in the armature, I had some duff (soft) brushes and the slight resistance they had at contact area as carbon built would cause the dynamo to stop working (by preventing the self generating at start up) at a pretty consistent 400 mile mark, cleaning the commutator got it working properly again, for a while, but new brushes fixed it properly.

The fault was puzzling as all resistances and wiring etc all checked out ok, but it would not do the self generating side of things, at start up, if I gave the field a “zap” of 6v with engine running the dynamo would continue to generate just fine, until the battery was fully charged, and then it would stop working again.

I suspect many cases where a “flash” cures the problem have a root cause of a dirty commutator and/or duff brushes.

[IVO]

Hello KiwiGF
Just mulling over a persistent dynamo no charge problem and I came across your post. My GF is only charging when I'm doing over 65mph at the moment, not helpful! I pull out the dynamo, has fitted new Lucas brushes, clean up com, flash it and put it back check out all wiring and DVR2 and it works nicely. Leave bike for 2 weeks then go for a ride and no charge unless I'm braking the speed limit! I'm doing this repetitively so fancy getting of the roundabout. I suspect I may have a similar problem with the brushes so did you use new Lucas ones or old stock ones? 
Cheers IVO