Ariel Owners Motorcycle Club

I Have a 1955 Fieldmaster which the previous restorer had converted the electrics from 6volt to 12volt. New loom and bulbs and battery but the bike is still running a 6volt dynamo. The ammeter shows a discharge when the lights are turned on but no charge when running at anytime (lights on or off). What would be the answer re a 12volt dynamo so it charges? Many thanks

I'd put a voltmeter on the regulator and see what is coming out - then have a look at the regulator and see what type it is...

Hi Peter,
For a 12 volt conversion the restorer should also have either changed the old armature in your dynamo for a 12v one or, better still, to have changed both the armature and field coils for 12v items. You can check the dynamo output voltage by disconnecting the 'F' and 'D' wires from the dynamo so it is completely free of the wiring loom. Then by strapping the 'F' and 'D' terminals together with a short piece of electrical wire, connect one lead of a voltmeter to the strapped terminals and the other lead to the bikes earth (if negative earth connect the negative lead of the voltmeter, if positive earth connect the positive lead from the voltmeter). Once the voltmeter is decently connected up, start the engine and carefully increase the revs. Voltmeter should show a good rise in voltage well above the expected 12 Volts as the revs rise. Don't hold it at a higher voltage level for too long, just long enough to read the meter. The voltage regulator on the bike should regulate the output to suit demand. If the check works then you will need to check your regulator as Simon has indicated.
Good luck with it,
Regards,
Keith.

Thanks to you both. Gives me a direction to go in

A standard 6 volt dynamo will still put out 12 volts or even more as controlled by the regulator and battery. The reason for changing the armature ans fields coils is that the 6 volt ones require higher revs before they will balance the load and the 12 volt ones will bring it back to balance, with lights on, at about 30 mph. Depends on many factors of course - condition of battery and other components, wattage of bulbs and gearing. The 12 volt versions do make a lot of difference, something to do with different diameter wire thus a different number of coils.

The question is, if you were starting from scratch (and I appreciate the OP has already converted most of the components) would you bother changing?

I have the dynamos for my KHA project and my LG project being refurbished at present. Both dynamos will be run at 12 volts because all my bikes are 12 volt. But the LG dynamo will use 6 volt armature and field coil while the KHA one will have 12 volt armature and field coil. The reason for the difference is that I am unlikely to use the lights on the LG to any significant extent whereas I am likely to use those on the KHA from time to time.

For me, a major reason for using 12 volts is that if you have a bulb blow when away from home, the chances of finding a 6 volt replacement, especially when abroad with language difficulties, is pretty thin. But 12 volt bulbs are readily available.

A point to consider.

You said a 'previous restorer'. Did said restorer 'flash' the dynamo field coil in order to induce magnetism into the keeper? Has the bike been standing a long while, as the magnetism in the field coil keeper can ebb away over time.

12V = lower current. More efficient.

Paul J is correct, 12V bulbs are easier to get hold of.

I ran for ages with a 6V setup with a 12V battery and bulbs.

I have now just rebuilt my dynamo with true 12V armature and field coil from Rev's Speed Shop, a Hella headlight reflector/glass assembly and an H4 bulb.

hi i use all leds bulbs and if the dynamo packs up the lights will run for hours on the battery, i run my NH without a dynamo and the lights last for ages on the battery