Charging problem

[scooterdoc]

I recently noticed my battery was going flat, so put a gunsons start check across the battery and it told me that the alternator wasn't charging

I obtained a second hand one and things have got worse, I put tester across battery and it shows full charge, start van and it drops, rev the van and it drops even lower, any ideas?

No obvious current drain, all extras like fridge etc disconnected

I'm baffled

[irish.david]

Try checking the voltage at the alternator when the engine is running and compare it with the voltage at the battery, also with the engine running. Anything more than about 0.5v difference and there's a problem somewhere....

Dave