my '61 BSA super rocket is negative earth... really?

[trevinoz]

Actually the whole end is different, cover, brush plate and end bracket.
The end bracket has a groove around the circumference for an O ring.

[duTch]

 
  Geez TT-  My Apologies. ...I must've had another dyslexic moment. ...I read that as something like 'Wire polarity doesn't change for change of polarity.'...Now I'll just pull both feet outta my gob and put them back in my boots but leave the socks in place+ Richards green 'Cone of Silence'...

       

[Triton Thrasher]

Is it fixed yet?

[mikeb]

not fixed yet. its a metal end cap. i flashed the dynamo field coil (F=green, both F and D disconnected from the wiring) and now when joining F and D there's about 0.25v coming out at about 1500rpm engine speed.
I'm now reading up the threads on dynamos (which is turning).

mike

[Triton Thrasher]

Something that has worked for me is to run the engine at about 2,000 rpm with F and D connected together on the terminal of a headlight bulb and the base of the bulb earthed to frame. If they do not light the bulb, then briefly connect battery live to your F and D.

Battery earth side must, of course be connected to frame.

That wakes up a dynamo that has forgotten its polarity.

[wilko]

Are you double sure you're spinning it the right way? Also I did this test recently and got about 2volts.After much headscratching I tried another drill with a faster speed and suddenly lots of volts.

[duTch]

 

It is possible to swap the strap type end cover for the one piece metal one. Just need to file down a small locating boss from the end housing, 

  Haven't got around to looking at the different bits yet, work's interfering with life- but maybe I've hybridized one with a lug/boss and 'O' ring, and I seem to recall rather than grinding a lug off, I decided it better to carve a corresponding notch in the cover with the dremel. ..

[mikeb]

ok so flashing the dynamo the 'usual' way achieved nothing for me. What did work is  triton thrasher's trick of wiring a 12v bulb between (1) D+F and (2) earth, then touching live battery to the D+F while the engine is running. this started the dynamo (I guess energized the field) and it produced variable voltage (6 to 12+ V) according to revs (as it should). its a 6v system.
but when the engine is stopped and then restarted I need to repeat this live flashing.

is this normal? does the battery via the regulator essentially prime the field in this way when its all assembled/working? is this when people say put it together and take it for a long ride?

thanks

Mike

[Triton Thrasher]

The casing is supposed to retain enough magnetism to start charging.

I have little electrical knowledge. I've heard excess distance between armature and pole shoe blamed for this needing a boost from the battery to start charging, but I don't know.

In the past, with a lazy dynamo like yours and with an electromechanical regulator, I have fitted a car-type charge warning lamp between dynamo D and a switched battery live. With regulator points closed, that let a little current into the field, or something like that and the dynamo behaved itself.

Maybe doesn't apply to solid state regulators. Anyone know?

Sometimes a dynamo just needs a few miles of riding, to start working.

[wilko]

A new field coil on ebay fixed one of mine with similar symptoms.

[trevinoz]

Mike,
              This can be caused by a film on the brush rubbing surface. Try cleaning the commutator and give the face of the brushes a rub with abrasive cloth and see what happens.