Charging puzzle

[PaulM]

Hello, I am a long-term BSA rider and well used to the foibles of Lucas equipment, but have been surprised recently by the behaviour of the ammeter on my A7SS.  The charging system is working fine at speeds of up to 55mph.  Above that I have noticed that the ammeter shows a strong discharge of 6 Amps, whether the lights are on or off.  If I drop back below 55mph, the ammeter needle shows +1 Amp charge, as normal (with or without the lights on).   Could this be a result of vibration affecting the ammeter, or is it likely to be a 'real' electrical fault?  The dynamo was recently rebuilt professionally, and the bike is fitted with a solid state regulator. 

I'm not sure how I can test the wiring or the electrical components as the 'fault' only happens at high engine speeds.

Has anyone seen anything like this?

[Butch (cb)]

I think you should find that once you've pulled through around 90 it will sort itself again.

[duTch]

 Hiya PaulM- maybe it's the ammeter...mine does similar but different; sometimes goes off the dial on the + side, and then settles down....mechanical reg, so thinking it needs adjusting, seems to charge ok otherwise though....

    Just between you and me, before you're busted I reckon you should sneak over to the 'Intro' page and do the appeasement stuff....

[a10 gf]

Connect an ammeter (using a small mulitmeter having a 10 or 20 A DC readout) in series and go for a ride, you'll see if it's really a discharge, or a bike ammeter fail. ....of course, be very careful while riding + looking at the meter !!

Or run the engine with the rear wheel off ground (using a well secured means of lift).

[Triton Thrasher]

Do what A10GF says, but just rev it up in neutral.

 Brushes not free to slide in their holders can cause a failure to charge at higher rpm, but that doesn’t explain where your 6A is going, unless you have electronic ignition and one of the dodgy types of regulator.

[a10 gf]

but just rev it up in neutral.

.. yes, obviously that's all that's needed wrote too quickly  :O)

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And welcome to post and intro, some story\pictures always appreciated.

[groily]

You could also just disconnect the battery and give the beast a test run to see if the needle goes through the same motions?
If it shows a non-existent 'discharge' on test, then the ammeter is unwell.

 

[PaulM]

Thanks for all the suggestions, I'll work through them.  Trying to find my way round the Forum, will get a photo in my profile as soon as I can find a way how to do it. 

[muskrat]

G'day Paul, nice avatar.
It could also be harmonics playing tricks on you. Take it out of it's position, extend the wires and mount it close with a bed of foam (gaffer tape, zip ties).
I had one doing this 20 odd years ago after an engine rebuild with different balance factor on the crank.
Cheers