OT moped charging circuit

[Dave]

Sorry for the OT but I've spent ages trying to find info about this problem and I know there's wide range of experise here and so in hope...

I'm trying to help my son fix his moped from his telephoned information that "The battery runs down in a few hours". Basically I know nothing about moped circuitry and there seems precious little help on the web about this. I can't even locate a workshop/service manual for the machine (A '92 Yamamha Slider). Anyone have a circuit diagram/description/any information about this kind of moped? I don't even know what the battery voltage is - I guess 6/12V lead acid(?). I'm planning a visit next week so would very much like to take kit to try and help him. I can measure the current drain in case something is taking current with the igition off - but I think it may be the charging circuit that's at fault. Is this similar to a car - alternator, (sealed) regulator module, battery? Your help much appreciated.

-Thanks

[Harry Bloomfield]

Dave formulated on Sunday :

I don't know the bike, so I can't be certain the following is correct:-

Most likely it will have a small alternator. This will provide an AC voltage to a rectifier module, which converts the AC to the DC supply needed to charge the battery. There might or might not be a regulator unit. The latter limits the charging voltage to the battery to the correct level. The rectifier and regulator might well be combined into one unit.

To check the battery is being charged, put a volt meter across it then check the voltage rises from around 12.5v (6.25v) to around 13.8v (6.9v) with the engine running for a 12v system (or in brackets for

6v).

Less than the engine not running voltage above, would suggest the battery is discharged, or that it is faulty.

To check if the battery is being discharged... With everything turned of, disconnect the the negative battery terminal and connect your test meter between the negative lead and the battery negative connection, set to measure DC amps. There should be no reading, or at worst a few microamps of of current flowing.

[James Salisbury]

The bike has a SHUNT regulator on their small alternator, one mode of failure is haveing a jump from a car. If the car engine is started the BIG alternator on the car will have no problem smokeing the shunt regulator on the bike!!!

[Dave]

Ah... the moped *was* jump started from a car (I have subsequently heard) so I guess the shunt is no more. I don't know if the car engibe was started or not - but maybe even the car battery could have the same effect. However the moped

*was* giving trouble before - not starting on the electric starter due to a flat battery. I'll need to take my entire workshop along to sort this lot out.