How to check if charging circuit is working?

[locksmith]

On the WR250 yesterday, the battery went flat. Just clicking on the starter, no headlight, no horn and the clock kept resetting when i hit the kill switch. Thank god for kick starts although half way up one really slippery hill I stalled it and that was fun
 I'm assuming the batteries knackered and will chuck it on the optimate in a minute (got to clean the bloody thing first- yuk!).
Before I rush off and get a new battery I suppose I should check that the charging circuit is actually working. How do I do that, I've got a multimeter by the way.

[Fazerider]

Easy with a good battery, just look for volts rising as you bring the revs up. Should level out at about 14V when the regulator kicks in and dissipates any excess as heat. At middle of the rev range it ought to be able to maintain the battery voltage at that level even with the headlight on.


With a dead battery, not so easy to judge. You should at least be able to see some rise in voltage.
If it gets much over 14V the regulator has packed up in which case it'll kill a new battery. (You'd probably also notice lights being rather bright and the pong of boiling battery.)

[locksmith]

Kick started it. Was around 14v at tick over. Gave it a few revs and it dropped to around 10v.
Optimate said battery is focced after around 10 mins of plugging it in.

[Fazerider]

Puzzling.

14V at idle sounds fine from the point of view of the charging circuit, but the voltage shouldn't drop as the revs increased, unless you also turned on the headlight. What was the battery voltage before you switched on the ignition?
It could be that the regulator detects the battery is duff and crowbars down to a lower voltage for protection, but I can't really see the point of making one that clever. Best thing is probably to buy a new battery and check how it behaves with a good 'un.

[locksmith]

Didn't check the voltage before. After testing it the igniton lamp and clock wouldn't even come on!
New battery ordered so I'll see what happens. Got the manual out and it tells you where to plug a meter in to check the charging so we'll make sure it's alright before we possibly knacker a new battery