low voltage during idle

anonymosaurus_RXS

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Hello,
Have a Yamaha XS400 sh andIm having to charge my battery once every two weeks.
i’ve tested using a multimeter the stator (which is running its specs) and the reg/rec (running to specs). i’ve tested for amperage draw, get none. pretty sure everything is grounded fine.
still, my bike won’t seem to charge itself. the most voltage i get during an extremely high idle is barely 12.7 V. is this a Voltage regulator issue, and has anyone tried to adjust the charging screw like it says in the manual? i’ve scoured forums but all i see is replacement threads and i’m wondering if anybody has actually adjusted the voltage regulator per the manual??
 
Unlike cars many bikes do not fully charge at idle, they rely on the rpm coming up enough to charge at just past that. You'd have to check for the proper numbers in the service manuals.

Take my Honda 550 and 750 and even the 900, they do not charge to hit the break even point until around 2000-2500 rpm but it quickly ramps up past that at street driving rpms.

If the battery is old; well of course they can run down and all the charging on earth won't stop that.
 
the battery is new and even over 5000 rpm the most voltage im reading on battery terminals is 12.7 V.
wondering if you’ve tried to adjust the voltage regulator? apparently there’s a mechanical screw in there that can adjust charging voltage?
 
check the 3 white wires out of the stator, could be that one is down either through the stator or the wire has broken somewhere
 
stator checks out fine; am getting .6 ohms from each wire. reg/rectifier seems to be within specs too. just took off voltage regulator and there is no access to it so no adjustments possible there.
is there any way to test the voltage regulator to see if it’s supplying enough power?
 
There's a resistor that can be checked on it (see Haynes manual), but really you've been doing the tests and it's been failing.

That being said, all the tests you've been doing should be done with a fully charged battery. Put it on a charger overnight and redo the tests you've been doing if it wasn't charged.
Also check the field coil. Should read 4.04 ohms +/- 10%.

If everything else checks out I'd replace the regulator.

Could go to a combo reg/rec or get a solod-state regulator.
I have an adjustable regulator on mine. Will double-check the model number.
 
just checked field coil from stator side wires from green to black and i’m getting the correct reading of 4 ohms. will charge over night and revisit, but it’s sounding to be like i’m in need of a new rec/reg. battery putting out around 12.3 volts at idle, and when idling at 5k it only pushes up to 12.7 V.
i was thinking this would mean a poor alternator performance but all my multimeter tests say otherwise.
 
The reg is probably dead, 12.7 volt is battery only with no charging at all hardly, that would be all 3 stator legs dead.

Adjustable regulators are the pits; they are super old junk and nobody uses them as solid state is whopping better, they self adjust on the fly.
 
The reg is probably dead, 12.7 volt is battery only with no charging at all hardly, that would be all 3 stator legs dead.

Adjustable regulators are the pits; they are super old junk and nobody uses them as solid state is whopping better, they self adjust on the fly.
is there a particular solid state regulator you would suggest?
 
I have no idea, just that in general older adjustable are not as good. From working of lots of stuff besides Yamaha. I know for instance that on old American Motors cars it was the difference in trouble every time you turned around to zero trouble ever again. AMC went to totally electronic way back in the late '60s and well ahead of most. We still use that same one even on Honda 750.

I'm sure somebody here will pop in with an idea.
 
before i swap out the reg/rect i wanted to make sure of something.
when i am testing for ground from the stator wires to the engine case, i get a reading of 0.8 ohms. not sure if this is supposed to happen... thoughts?
 
well y'all. think i've finally found my issue.

went into left-side panel to clean out my sticky clutch and found out that PO had pinched the stator cables between the left side panel and the engine instead of routing them through the conveniently placed cutout. :wtf:
can't imagine meeting resistance on the hex bolts and continuing on, but we are not all made the same.
so, at the present it makes sense to me that i am losing power due to a severely pinched cable that is most likely grounding out most of my power. i mean these things are pinched to hell; so much that the wiring is exposed and in all likelihood, two wires pinched so tight they've fused together. sounds like i'm due for a rewire...
thanks to all who've chimed in thus far. :cheers:
going to take pictures for future forum-searchers and will try to keep this thread updated for archival reasons.
 
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