Dynamo help

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electrajohnt
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Re: Dynamo help

Post by electrajohnt »

Well bless my soul, it works.
I did as Groily suggested, put a twelve volt bulb on only when the meter was reading the 18v and it lit the bulb no problem at all.

I will now put back onto the bike, if it still refuses to charge it must be the Wassel regulator I put on last back end, it was charging before I put it away but has steadfastly refused to charge since I got it out this year. The regulator has done less than fifty miles, hopefully that will be ok.

Thank you Groily and all others who took time to help.
JohnT
JohnT
electrajohnt
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Re: Dynamo help

Post by electrajohnt »

Another update
Tried it with the 6v bulb and it blew it.
Put it on the bike, it’s a Venom by the way, and put the the drill on it, it’s showing a charge. Very grateful for that. But confused, Why is it now showing a charge, done nothing except strip it and clean it, a light rub on the commutator with smooth wet or dry, now it’s charging. No wonder it is called electrickery
Thanks again all concerned.
JohnT
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Groily
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Re: Dynamo help

Post by Groily »

Very pleased you have a result John.
It's working because we have now restored a bit of remanent or residual magnetism in the pole shoe for the field winding and the dynamo 'yoke'. It should have happened when you were trying it as a motor off a battery, but it doesn't always.
The usual cause of difficulties is disuse, owing to which the trace of magnetism left over from last time it ran which is needed to get the dynamo to self-excite can pretty well disappear. The trace left isn't enough to get things going unaided, but if the thing can be encouraged to sling out some load-free volts (as in this case), then putting a modest load on will often bear fruit and bring it back as if by magic.

When things are enfeebled, there's a limited chance of lighting any cold bulb from rest, and sometimes a 6v won't light up even when the dynamo's dyning. A 12 volter is more obliging because it demands half the current. An added advantage is it will not as easily blow with increased dynamo speed.

When it's re-learnt its good behaviour, a dynamo should then light 12v bulbs starting from rest as the volts build up, but maybe not cold 6 volters. It OUGHT to stay on best behaviour going forwards, but they can be capricious things. (You may find after a lay-off in the garage that it's reluctant to fire up again some point in the future, but let's hope not!)
electrajohnt
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Re: Dynamo help

Post by electrajohnt »

If I now put 6v LED bulbs in would it be easier for the dynamo to produce electricity. Reason for LED’s is so I can run headlight in the daytime. Just been a run around and it charges ok but with headlights on it does drop into not charging unless revs are kept up then the ammeter will go into the positive side.
JohnT
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Groily
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Re: Dynamo help

Post by Groily »

Be easier on the battery around town or at low revs, yup. LEDs would draw maybe 15-20% of the current needed for a halogen bulb (say an amp or amp 'n a 'alf versus 6A) so obviously less demand on the system and ammeter into positive territory pretty fast.

Not sure what min speed in top gear is on a Venom as it's a while since I had the pleasure, but let's say 35-40mph . . . at which revs a 6v dynamo ought to be able to balance the load of a 35W headlamp and tail and speedo just about.
(Normally speaking it would need somewhere around 1750rpm engine to balance that sort of load on one of our Machines of the Marques, with full voltage regulation happening from about 1850-2000rpm, but I don't know what the dynamo to engine speed step up ratio is with the pulley system on a Velo.)

The cheap and cheerful Wassell regulators aren't exactly top of the range though, in terms of how fast they reach full regulation, what voltage they maintain when regulating, or how well they behave with descending revs. The products from Al Osborne and from Dynamo Regulators Ltd are a lot better - it's 'get what you pay for' with these, they don't all work the same way however similar they may look).

LEDs have many admirers - but my own LEDs don't cast a great light for night riding. More recent ones are better and there are loads of comments on here and other forums about their performance. I like them on bikes I want to be seen on, not on bikes I want to see by, on which latter I prefer those old concave Cibié units with modern halogen bulbs.
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Re: Dynamo help

Post by Group Leader »

If you do buy a a new armature make sure that the bearings are a reasonable fit. I've had two new armatures from different sources and in both cases the journal for the main bearing was over-size and no amount of freezing the armature and heating the bearing, as is often recommended, would enable the bearing to seat properly. I didn't appreciate on the first one and used rather too much force and even then, it didn't seat truly properly which pre-loaded the commutator bearing and led to an early and spectacular death. On the second one I did the proper, engineering job by turning the journal down (it only needed a couple of thou but they were very important thou!). There's a thread on here somewhere concerning my dynamo exploits.

Alan

UPDATE: Here's a link.

viewtopic.php?f=17&t=21116&p=206333&hil ... re#p206333
1953 AJS 16MS, 1939 BSA 250 and a 1/3 scale Sopwith Triplane but that's another story ..... :lol:
Groily
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Re: Dynamo help

Post by Groily »

Just a small addendum JohnT. Your Velo would have had a Miller DVR dynamo originally, I think, a 60W job equivalent to the longer E3L Lucas broadly.
What you've got there is a 45-ishW short Lucas. Doesn't matter at all, but it is relevant to the wattage of a non-LED headlight bulb maybe, and makes, in my opinion, LEDs 'a good thing' for your purposes.
A Venom I used to ride now and then was 'Miller', converted to 12v with the field coil wiring reconfigured to run with a DVR2 regulator, and it was actually very good as long as one kept the revs up a bit. It was always ridden 'lights on' by day, and served well.
electrajohnt
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Re: Dynamo help

Post by electrajohnt »

Hello again,
Another update from confused and bewildered. Just been for a brisk runout and no charge from dynamo, first time out since dynamo showed charge fitted to bike but driven by drill. It shows healthy discharge when pilot or main beam switched on.
I was wondering, as the dynamo started to charge when a 12v bulb was connected, this then seemed to initiate the the 6v charging, could I put a false low wattage twelve volt to kick it into action, say by putting a 12v into the pilot light circuit instead of the 6v ( nobody uses pilot lights anyway nowadays do they?). Would that work.
JohnT
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SPRIDDLER
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Re: Dynamo help

Post by SPRIDDLER »

Which regulator do you have?
I haven't trawled back through all the thread but those symptoms sound like a similar issue I had with my AO regulator as it wouldn't 'wake up' and start the charging process unless I gave the engine a good rev. Every time the revs dropped I had to slip the clutch and go through the same revving process. In traffic, particularly with the lights on it was a real PITA.
I changed it for a DVR2 regulator.
'There is a tide in the affairs of men
Which taken at the flood............'
Groily
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Re: Dynamo help

Post by Groily »

Playing with a 12v bulb when testing a dynamo not connected to battery or regulator is just an easy way to get it to kick in, as the 12v bulb needs less current and is easier for the dyn to light than a 6v one. On the bike, the battery provides the current surge necessary to get bulbs to illuminate, so
with the dyn connected up to battery and regulator, I don't think it makes any real difference - the dynamo should kick in when the voltage it's producing exceeds that of the battery, thanks to the cut-in / cut-out function of the regulator.

If the dynamo is still producing all those volts if you bridge F and D as before (??), it therefore ought to be sufficient - but some dynamos, especially those that are out of practice as it were, need a big handful of revs to cut-in from cold, and then behave normally afterwards.
A reluctant one may regularly need that handful of revs to cut in from cold. Some good long runs to get the thing thoroughly in the mood is also a possible aid to future behaviour.

This could come back to the speed of rotation perhaps on the bike (on a typical Lucas installation the dyn turns at give or take 1.25x engine speed, I don't know what the gearing is on the pulleys you've got) - or it could be the Wassell regulator you said you have.

You could try touching the F terminal with a lead from the battery live terminal very briefly while the engine's running to see if that gets the field up and running properly with some direct help.

It may help to have a quick read of the attached doc if it shows up, which explains as best I could when it was compiled in another context, how these things actually work, and what they are doing at each stage of operation. Yours works, we know that. It's not the right generator for the machine, but that should not be relevant as long as it's turning at whatever speed it's meant to turn, and is hooked up to a decent regulator.
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