Neg or poss

Information relating to the Matchless G80 or AJS Model 18 500cc Heavyweight.
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thumper500_LAPSED
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Joined: Wed Apr 21, 2010 6:21 pm
Location: LONDON UK

Neg or poss

Post by thumper500_LAPSED »

I have 46 G80 can anyone tell me if I have neg or poss earth.
When I push down onto the top of the regulator the amp needle goes to + with the black connected to live and brown wire to earth on battery. Spin the wires and amp goes to —. Bike not running to test.
Thanks
Groily
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Joined: Thu Jul 04, 2002 1:00 am
Location: NORMANDIE FRANCE

Re: Neg or poss

Post by Groily »

This is one of these 'If you want to get to Dublin I wouldn't start from here' things!

Somewhere in the Archives it probably says what the earth was originally, if there's a wiring diagram for the model / year. Just guessing, Pos earth. But to be honest, doesn't matter what the ammeter says when you swap things around the way you have, you need to start with a decision only you can make - which earth do you actually want?
Then - and this applies just as much if you don't care! - you need to see which way the dynamo is polarised, and change it if it isn't what you want or follow it if it you are OK with it. Everything starts there, the battery is just the recipient of the largesse of the charging system, if it works! To find that out, you have to get the dynamo up and running and see what comes out, if anything.
See the Matchless Clueless website for all things to do with testing and verifying dynamo set up, polarity and output.

If and when there is some output, then you need to hook up the regulator - a mechanical one isn't bothered about polarity, but all modern electronic ones are, so don't hook up a pos earth generator to a neg earth regulator or you might break it, some of them don't like it up 'em Cap'n Mainwaring.
You need to get the 'A' wire from the regulator to the side of the ammeter (and the switch) so that (engine off) it shows a discharge on the ammeter when, with the battery connected according to the polarity of the dynamo, you put some lights on. Regulator F goes to Dynamo F, regulator D goes to Dynamo D, and the 4th wire is earth.

It's entirely up to you which earth you go for. Dynamos work just the same both ways. Most post-war Brit iron is positive earth, until at least the mid '60s, but neg earth has some advantages if folk want to hook up any modern gizmos that need neg earth. Many pre-war beasts were neg from the start, like pretty well all foreign machines, and Rolls Royce from Day One.
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Rob Harknett
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Location: ESSEX UK

Re: Neg or poss

Post by Rob Harknett »

Surely its easier to look in your bikes instruction book for the answer to this question.
http://archives.jampot.dk/book/Owners_m ... Manual.pdf
You've probable been pushing the CVC changing the dynamo polarity.
thumper500_LAPSED
Posts: 8
Joined: Wed Apr 21, 2010 6:21 pm
Location: LONDON UK

Re: Neg or poss

Post by thumper500_LAPSED »

Thanks for the reply’s. Book says neg earth but I did not check battery before I took it off. I have bought a DVR2 with poss earth.Bought before checking. Not sure if previous owners had changed it to poss earth. Best leave it until it’s up and running next year.
Thanks
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