MK III/ES Commando: Checking Reg/Rec

Hi Mike,

The advantage of using the bulb is even non-electical people tend to have one and it does put a load on the system.

You can use a meter, set to AC volts. Disconnect from the rest of the wiring loom.

Start the bike and you should see maybe 15 - 20 volts at tickover. Remember this is on no load.

Now connect back to the loom and test again, at tickover you may get 10 - 15 volts and this will go up with the revs.

If you go onto the battery (meter to DC) then you should see around 13volts if the battery is charged and this increases up to around 14V with a handfull of revs.

If you have the volts at the alternator and no charging volts at the battery then you have a problem.

Either wiring or the rectifier subsystem. This consists of a rectifier under the seat (round black disks with 3 wires on) and two zener diodes, one on each footrest plate.

The alternator wires (green / Yellow and White / Green) go onto the rectifier and also down to the zener diodes.

The Brown / blue from the rectifier goes (via the fuse) to the battery.

Check everything is tight and volts at one end is getting to the other.

Regards

Tony

Dear Mike,

As you have already been advised above there are different areas to check to sort this issue. Here are more precise instructions folow or ignore

Start With Alternator; Disconnect at bullet connectors below air filter and setting multimeter to 20v AC start engine and find out what output voltage is. this is bit you can check with headlamp bulb which should be bright.

Assuming alternator passes reconnect bullets, find same 2 wires at rectifier and check voltage there is same value with engine running.

Assuming it is now disconnect output wires rectifier and use multimeter DC scale to check output if 13+ then ok

If that passes rejoin wires and move on to battery voltage record with engine off, start up and see if it rises to 13 if it does then charging is Ok and battery is duff.

If not run engine for a few minutes, stop and feel temp of Zenner diode if it is hot already then it may be the issue. Not very easy to test unless you have standard points ignition. If you have then just pull of spade connector and see if that increases battery voltage with engine running for a few seconds. If you have electronic ignition do not do this as it will be damaged

hope this helps

Above has a degree of miss information and time wasting and missing the point. Measuring the AC out of the alternator is partially useful BUT much better to use the spare head lamp bulb AND test down to earth.The full test is on my web site AOServices.co.uk

Next point, a standard MKIII does not have a reg/rectifier (mentioned above) so do we have the original system (half bridge rectifier with two zeners completing the bridge)? or has this really been changed to a reg/rect? IF the latter I can check (send it to me with £5 to cover postage)or you can replace a reg/rect with a traditional bridge rectifier for test purposes only. If a bridge rectifier restores charge it will be unregulated so if you must ride home then keep your lights on.

If any one needs any more information on these points please phone me.