EL009 ELECTRICAL

Now that my Viper is running beautifully I've turned to the last remaining problem which is that the dynamo is not charging the battery. I tried the test suggested in the service manual viz. pressing the cut-out contact together with the belt removed and that only produced smoke!
Looking at Q&A EL004 you suggest connecting the battery to terminals D & F but the diagram of the dynamo on page 76 of my Velocette Service Manual doesn't show a terminal F. Is terminal S the same? This would put 6 volts through the field coil and resistance winding in series.
On dismantling the dynamo I find that it has been subjected to the same butchery as many other parts of the bike. The commutator segments correctly show 0.2 ohms but the field coil shows 2.9 ohms instead of 4 ohms stated in the manual. Additionally there is no resistance winding so the two green wires are missing, only 2 wires from the field coil exist. An extra wire has been connected from terminal S to brush A.
So several questions arise.
Has an incorrect field coil been fitted from a different bike with no resistance coil? Is the extra wire a substitute for the missing resistance winding? (may explain the smoke) Can you tell me anything about this resistance winding so that I can try to buy one?
As the armature, field coil, brushes and bearings seem OK I'm hoping to rescue the dynamo without too much expense.
Dynamo is Miller type DVR and bears the number 029738 on the pulley end bearing housing. - Frank Dunning 12/8/2002

Glad to hear the Viper's still running well.
I agree that your dynamo should rescue OK, since the important bits seem sound. It seems that you have a Miller dynamo but I'm not clear what type of regulator - might it be an electronic one?
EL004 related to a Lucas dynamo, which has simple connections in the dynamo - there's just the armature (i.e. the brush connections, D and Earth) and the field coil whose connections are F plus Earth. All the rest is in the Lucas regulator. When you wire in a JG unit to a Lucas setup you don't directly change the connections at the dynamo end, all the changes happen at the regulator ends of the wires.
But when you fit an electronic regulator instead of a Miller, you do have to change some of the dynamo wiring.
With a JG, this is just a matter of physically removing the cutout and connecting an insulated wire between the D and the A terminals.
A wire from A to S (S isn't the same as F on an original Miller setup, though it does become equivalent to the Lucas F terminal once a JG has been wired in) doesn't sound right.
The possibilities grow rapidly depending on your components - you imply that there is still a cut-out inside the dynamo end-cover, but what type of regulator do you have? If it is electronic, or a Lucas Regulator is in use, you wouldn't then need a Resistance Winding. By itself it might not matter if the Field resistance is a bit out.
Before looking for a new Resistance Winding I think we need to establish exactly how your dynamo is currently (supposed) to be regulated.
And with all leads disconnected a 'motoring' test is still worthwhile - remember all you need is 6v to one end of the field coil and one brush; and the other end of field and the other brush and the battery all on a common earth. But you have to make sure nothing else is connected/shorting! - TW 12/8/2002

The dynamo motors fine so no apparent problems with the windings.
I now think that the wire from A to S is a ground because the diagram I have suggests there should be a grounding strap to the brush, inside the end plate, which is missing on my dynamo.
I don't know if the regulator is a Lucas because it is unmarked. I'd be surprised if it's electronic because judging by the state of the bike when I got it I don't think it had been on the road in the last 20 years. Anyway I've attached pictures of the regulator and dynamo for your opinion.
My understanding is that if I buy an electronic regulator I can do away with the cut-out and resistance winding. If that's true it appears to be my best option. Also I don't know if the present regulator works. By the way it's mounted on the mudguard and I have run a separate earth wire to it for a good connection.
Can you advise me on this, and if I buy an electronic regulator I assume I will get full wiring instructions? - Frank Dunning 13/8/2002

Glad to hear the dynamo is 'sound'
Your regulator is the original Miller cartridge type as fitted by Velocette along with the DVR dynamo.
It's probably given good service from new, and may now have only a small fault; or it could equally be scrap.
If you thought you were likely to restore your bike to 100% original one day, you could get both the dynamo and regulator restored by someone like Dave Lindsley (01706 365838).
On the other hand, if you mainly want to ride it then I do agree the best thing is an electronic regulator. They are sealed and seem to be trouble free.
A JG unit has three wires - two connect to the dynamo D and F and the other to the ammeter/battery. The unit has to be mounted in a way that is really well earthed. The only real problems arise if you don't get a good earth, or if you connect the battery with the wrong polarity, which kills the unit. It really is very simple once you've got the dynamo motoring in the right direction with its D and its F. The unit comes with wiring instructions, and mine also explained how to remove the superfluous cut-out and rewire the Miller DVR, and how to change the dynamo's polarity if necessary.
Your main decisions are:
12v or 6v - it is very nice to move up to 12v (makes buying bulbs etc easier) if you are prepared to change all bulbs and battery (instead of changing the horn I hide a cheap taiwanese one, and if I'm already using such a 6v one I don't change it unless/until it burns out, which it doesn't, but it gets really loud). The big problem is fitting the 12v battery in a way that doesn't look ugly - I don't think you can mimic the standard black case.
Polarity - JG's are available in either, but take the opportunity to go to negative earth.
Shape - DL used to be able to provide a sealed 6v unit in the same housing as your cartridge regulator, but again unless you want originality it's better to use the alloy unit under the seat.
Don't throw away the old regulator or cut-out etc - you or another enthusiast will want them one day! - TW 13/8/2002

I think I'll stay with 6V because I have already bought a new battery and 6V quartz halogen bulbs are readily available and bright.
I called DL and he's out of stock of the JG unit for a couple of weeks so I'll have to wait. I haven't been faithful to originality so the standard one will do.
When I rewired the bike I used a club wiring loom and wired it to the diagram that came with it. I assumed negative earth beause that's what the diagram showed but maybe the dynamo is for positive earth. How can I tell? - FD 14/8/2002

I guess you bought a 'VSL351M' loom, which is for the original Miller dynamo/Miller regulator/Miller switch and Miller lighting set combination. This combination was fitted by Velocette with a negative earth, and the VSL wiring diagram therefore shows the battery connections with a negative earth.
(Somebody might have changed your Miller system to positive earth, in which case you'd mainly have noticed by which side of the battery was connected to earth. And if you'd simply rewired it all and put the new battery in the other way round, that would have explained why you got no charge - assuming the lack of charging happened straight after your re-wiring!?)
When Velocette used a Lucas switch and lighting set for the Thruxton they changed to positive earth and soon after the Lucas dynamo and regulator replaced the Miller on all models and positive earth was used until the end. You can see all this in the wiring diagrams in the Technical Info pages.
There are instructions with the JG for checking and changing the polarity of the dynamo before starting to install the JG, since polarity has to match that of the JG you are installing. I won't try to reproduce them here unless you get into difficulties, (though next time I see Dave Lindsley I'll ask him if I can reproduce his JG documentation in the wiring diagrams section). - TW 14/8/2002