Changed stator, RR and battery. Still no charge at idle

[kenmyh]

Hello!

As the subject says. I've problems with charging on my Mk1. Last year I replaced stator, RR and battery after a full shutdown on a trip. The problem is that it still does not charge at idle. I've learnt to ride with this, since it charges as normal above 2000 rpm, but I wanted to try to fix this now. Bought a RR110 fra Electrex, and hoped this would do the magic trick. It did not. It started good, and were charging at 13,9V (for maybe 30 sec) when I started the bike, but as rpm dropped, so did the charging. I stopped the engine with 11,6V on the battery.
It still charges as normal above 2000 rpm.

Any ideas to what I can try next, or what the problem might be?

/Kenneth

[Art]

If your looking for short cuts there isn't any. You've replaced 90% of the charging system (battery, regulator/rectifier (RR) and stator) and still no joy! Question - Did you test any of those parts to prove they were faulty before replacing them? Assuming the replacement battery, stator and RR are all good, and there's no real guarantee of that, all that is left is the wiring harness, but don't jump straight in you'll need to start at ground zero following a logical sequence of testing to identify the root cause. There is no magic. A multimeter is your only friend here, start off with the battery and check/test in order:

battery fitment (12v, 8.6Ah and >150 CCA (EN);
battery level of charge (>12.5v);
battery holding charge (ignition on battery level of charge slowly dropp;
battery load test (>10v when cranking the engine for 5 seconds on full throttle - note full throttle disables the fuel system so the engine won't start/flood)
battery stand by current drain (<0.5mA ).

If all the above proves good and serviceable then continue to test of the charging system as described here.

BTW the Electrex RR110 is a down grade from the OEM (Shindengen) MOSFET RR

[kenmyh]

Thanks for the reply Art!

I tested everything today. Took the battery of the charger, and started the bike. When the engine is cold and the rpm is around 1800, it charge 14,02V and keeps this charging till around 1600-1700 rpm, then it slowly goes down. Stopped the engine when the battery showed 12,3V.

Did all the testa you linked to, and everything is OK. There is no sign of faulty parts, other than the voltage dropping at idle rpm.

Any other tips?

/Kenneth

[Art]

The battery voltage is expected to drop when the engine is idling at 1,200 RPM, 12.3v at 1,200 RPM is OK because at that point the charging system output will be less than the demands on the battery from the ignition system, lights etc.The voltage at the battery should rise as the RPM's rise which is why you should expect >13.5v at 2,500 RPM and around 14v at 4,000 to 5,000 RPM. If you're seeing less than 14.2v at 4,000 RPM that is because the battery is either not fully charged or not holding a full charge.

As a rule of thumb expect battery voltage -0.5v when the ignition is switched on, battery voltage when the engine is idling at 1,200 RPM and battery voltage +1.2v at 4,000+ RPM. For example, expected voltages across the battery terminals could be:

12.6v with the ignition switched off;
12.1v with the ignition switched on;
12.6v with the engine idling at 1,200 RPM;
13.8v with the engine running at 4,000 RPM, rising to 14v which could take an hour or more of riding at 60+ mph (95 kph).

[kenmyh]

The problem is that it is dropping as long as it is on idle. Last time I stopped the engine when the voltage had dropped to 11,3V. So it does not hold the charge at 12,3V.

[Art]

Assuming you tested the wiring loom and with the ignition switched off there was battery voltage across the RR output cables, and with the engine idling at 1,200 RPM there was less than a 0.2v voltage drop between the RR output cables and the battery terminals. In which case I'd suspect one or more of the stator coils is breaking down under load.

When the charging system voltage drops test for continuity between any one of the stator output cables and the battery negative terminals, expect no continuity. Or remove the stator for a visual inspection, what you don't want to see, or maybe you do, is blackened coil windings which indicate the coils are shorting out to ground.