Honda-SOHC
SOHC.co.uk Forums => CB500/550 => Topic started by: Rolfbulmer on October 01, 2026, 08:42:29 AM
-
The bike has been completely rewired using an motogadget m-unit. The alternator stator and field coil are working fine. I have fitted a 7 cable chinese aftermarket reg/rec with the 3 yellow cables connected to the 3 stator yellow cables, the green cable connected to the ground coming off the field coil, the white cable (excited voltage to field coil) connected to the white cable coming off the field coil, the red cable connected to the battery via a fuse, and the black cable (voltage reference) connected to a switched supply off the ignition.
All connections are good, the switched reference voltage is good, the ground is good - everything is good BUT the battery will not charge. I initially concluded that the chinese reg/rec must be 'out of the box' faulty so i bought a new one. This also did not work so I am thinking that something else is going on here.
Has any one got any ideas or had similar issues.
-
Is the green cable properly grounded, check continuity to chassis or battery -ve. Alternatively check for zero voltage between the Reg/Reg green wire and ground with the engine running.
You may have a green wire between field coil and new Reg/Rec but both need to be grounded somewhere. The original rectifier was bolted to chassis to pick up ground and also provided ground to the green wire.
Regards
Dave
-
Thanks for that.
I am reasonably sure the grounds are ok. I have the green cable from the field coil going into a 3 way WAGO. Also going in to this WAGO is the green cable from the reg/rec, and coming out of this, connected to a chassis ground is another green cable. Checked for continuity and all good.
-
What made you replace the OEM parts?
-
Do you have a multimeter to measure resistance and voltage
Warning, actually note the resistance measurement, don't rely on the beeper as they sometimes beep indicating a connection not necessarily a good one.
The connector that goes down to the alternator unplugged would originally have connected to the OEM regulator, ignition off.
Measure between each of the 3 yellow wires, 1-2 2-3 3-1 doesn't matter which ones, should be around half an ohm, the corresponding shop manual should tell you the exact value. Main point is they should be very close to each other. Any more than that value or differences between them, suspect a grubby connector between that plug and the alternator windings.
From the white wire which is probably connected to the new unit now , measure to ground you should see about 5 ohm, significantly more than that suspect a grubby connection between there and the field coil including the green which is the return to ground.
The grubby connectors may be hidden behind the front sprocket cover.
The red or red/White wire should go back to battery +ve. Not to the starter motor side of the starter solenoid.
If they look ok then Voltage measurements with engine idling
Meter on DC voltage
Battery voltage on black wire
Close to battery voltage on white wire going to alternator field coil, should reduce as the revs increase.
Zero voltage on the green wire going to the field coil
Switch meter to AC voltage, measure between each of the yellow wires going down to the alternator, anywhere between 25 and 40v AC depending on load.
A quick check if the field coil is energized, try sticking a small 10ml spanner to the honda logo on the alternator cover, you should feel it pulling the spanner as you pull it away.
Regards
Dave
-
Thanks for that.
I am reasonably sure the grounds are ok. I have the green cable from the field coil going into a 3 way WAGO. Also going in to this WAGO is the green cable from the reg/rec, and coming out of this, connected to a chassis ground is another green cable. Checked for continuity and all good.
Wago connector - clamped on the wire and not the insulation ?
-
Here’s a thought, but nothing probably to do with this issue. I ran my battery down on the 550 rescently trying to start my bike. When it eventually started it ran just fine, (lack of running) I then proceeded to take it out for a blast with headlight and running lights on about an hour and a half later I returned and checked the charging, I was surprised to learn that I was struggling to rev up and get 12.5v. Put bike on charge for a few hours and left it overnight. Went for a descent run the next day and came back checked charging voltage - up to 14.5 no problem on fast idle. So question is if a battery is below a certain voltage it will not take a charge from this system? It’s a yellow brick by the way!
-
Nope, you need to have some power to put into the field to get magnetism creating charge in stator for battery, if battery volts low you dont get enough flux so less charge
-
Also a health battery just needing charge is going to pull more current for the same voltage compared to a charged battery.
Since playing around with the adjustment on my regulator, it's straight up to 14 on a fast idle and topping out at 14.8 going down the Road Idling at traffic lights it drops down to 12.8 with the headlight on and about 13.5 with it off. Soon back up once the revs get up to 2 1/2
Much better than before adjustment where it was dropping below 12 in urban traffic with the headlight on.
Regards
Dave