Charging problem - bad rec/reg?

[Brett]

After the first 50 miles since I built my bike, the battery died (Shorai lithium) and the bike would not kick start. I charged the battery and tested the voltage across the battery and it's not charging (12.5 volts at idle and the same at 2000rpm).

I've gone through most of the usual checks. At first I thought it was the rotor as there is only 2.8 ohms across the slip rings. However the rotor and stator have been rewound. I spoke to the company in the UK that did it (very reputable) and they assured me that 2.8ohms was ok because the wire they use is thicker and it was tested to work. They suggested I test the regulator/rectifier.

I am not able to start the bike at the moment (to do the green wire test or a/c voltage between the white wires) but I did the diode test in the meantime.
I get correct readings between the red wire and the white wires, but NO reading either way between the black and the white wires.

I've done most of the other checks: There is just under 12v at the brushes and 0.5ohms between all three white wires from the stator. The rec/reg shares the same ground as the battery and there is good continuity)

Does it sound like the rec/reg is bad without doing the other tests? (could the black/ground wire be damaged inside the reg/rec?)

Thanks, Brett

 

[Brett]

sorry - it's an 1981 xs650 with all new and simplified wiring.

 

[gggGary]

it's not charging (12.5 volts at idle and the same at 2000rpm).

I've gone through most of the usual checks. At first I thought it was the rotor as there is only 2.8 ohms across the slip rings. However the rotor and stator have been rewound. I spoke to the company in the UK that did it (very reputable) and they assured me that 2.8ohms was ok because the wire they use is thicker and it was tested to work. They suggested I test the regulator/rectifier.

but NO reading either way between the black and the white wires.

Brett

I thinking I'm not buying the 2.8 ohms is OK schtick. That's 50 watts, double what the 5.6 ohm draws, a pretty bid chunk of the output. Did you weld with the regulator on the bike? All three AC to ground diodes blown at the same time is suspicious. But yes the rectifier's toast.

 

[Brett]

Thanks Gary. I don't really believe the 2.8 ohms thing either. I guess the tests with the engine running will show if the rotor is providing charge. Grounding the green wire to the rec/reg should show up the rotor as bad if the volts across the battery don't increase. Is that correct?

I've never welded with the rec/reg attached. I once briefly shorted the battery by mistake, not sure if that could have done it?

 

[gggGary]

I don't think shorting across the battery would bother the rectifier.
Yes check for plus 12 at one brush and short the other but with a blown rectifier it won't show charge. The white wires should show about 16-18 volts AC with the bad rectifier per curley's guide You could use any random 3 wire rectifier to test the other components.

 

[Brett]

Thanks Gary. I've ordered a new rectifier/regulator and I'll get back to it once that is wired up. I'll let you know how I get on....

Thanks, Brett

 

[Brett]

I fitted the new rectifier/ regulator and now it charges without a problem. I re-checked the diode readings on the old rec/reg and only one of the three red/white connections gave me a duff reading, so not sure why I got the readings I did first time round. Either way, the rec/reg was toast as you suggested.

I've yet to check exactly how many volts I'm getting at over 2000rpm, but a quick blip of the thottle showed about 13.5v. I know I'm getting a low resitance across the slip rings, but I've no reason to doubt the company that re-wired the rotor and stator as they are a reputable company and I'm sure the alternator is doing it's job.

Thanks for your advice Gary. Now I'm fully up and running and can enjoy some summer riding.

 

[trance]

Be sure to double check output by hooking up a volt meter and going for a ride. See if you get sustained output at highway speeds and RPMs.

 

[Brett]

Good idea, I'll do that. thanks