Charging problems

[wooster]

Hi All
I'm a newbie so be gentle with me. My Ulster replica isn't charging it's battery. I'm running a 12V dynamo. Initial thoughts anyone?
Cheers
Rich

[Bob Culver]

Charging questions recurred on the old site. Replies found through the Search function eventually covered most angles but I guess much will now have to be repeated.
Undocumented 12v conversions complicate matters. Helpful to know if dynamo 2 or 3 brush, had fields and/or armature rewound, has any sort of voltage regulator and type, whether fitted a field current limiting resistor, if summer charge retained, etc
Whatever, isolating the dynamo, linking the field and output wires should produce more than 12v from the linked wires to earth. Best measured with an analogue meter or judged from brightness of a bulb.
If that fails the standard causes worn brushes etc.
If tinkering beware the cutout not operated and left in that state with dynamo not generating.
Based on a small sample and all late 20s 1930s types, the 3rd brush prone to wear. Most original dynamos have been cooked at some time due output exceeding that to balance original 18w lamps. should not exceed 8-10 amps day charge on ammeter.
Should be low resistance continuity between isolated field wire and earth, and from isolated output wire to earth, more or less constant as armature slowly rotated.