Battery Not Charging at Idle

fR3ZNO

XS400 Enthusiast
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Hey all,

Hate to start a thread like this, but I am getting frustrated and would like some help.

Last fall, I had finally gotten my bike up and running and CHARGING. It wasn't long before the engine seized (had a rod knock).

So I put the bike away and started looking around for parts.

Fast forward to February, I picked up a minty fresh engine that had 960 miles on it.

Fast forward again to now. I got the new engine installed and running. But, the battery is not charging at Idle. The volts just slowly drop while idling. If I rev it up, the volts will slowly rise I was able to get the volts up to about 15-15.5v. Which is way higher than its supposed to be.

The stator wires passed the resistance test with them all at 1.0ohm, minus the 0.1ohm of the tester itself.

Now, I replaced the rectifier and regulator with a single combo unit in the fall and that was what got the bike charging.

I tested the rectifier anyway and it passed the diode test.

The field coil passed the resistance test with 4.1ohms, which is within the 4.0+/-15% ohms.

A razor blade also sticks to the stator cover.

I am thinking it is a regulator issue since the volts rise without stopping at the specified 14.5-14.8v.

But I am not sure how the voltage regulator could have gone bad already since it is part of the rectifier combo unit which is brand new.
 
I would get a oem style unit. There are lots of them around and work very well. These should charge even at idle.
 
I have seen them also. You need to do some searching and keeping your eye out. I got one a few years back for under $40. I also have picked up used ones for under $20 that test perfect.
 
Yeah. I'll look around. Just cant believe the regulator isn't working already.
 
So I got the bike charging again. I must have fried my new RR or something. I swapped the good regulator and rectifier from my dad's XS400, which were known to be good.
 
So, I ended up sending my old RR to electrosport and they sent me a new one. I wired up the new one exactly the same way and no it's not charging. Ugh. I need to check the fuses still. But instead of the volts going up with the throttle, the volts don't change at all. They stay right around 11-12 volts depending on how long its been running and draining the battery. I am guessing the regulator is not telling the stator to power up and charge? I am getting frustrated with this. I think I'm just gonna pick up a used OEM regulator and rectifier and be done with these shenanigans.
 
Indeed. I just bought a good used regulator off of eBay earlier today. I'll see if it'll work with the rectifier portion of the electrosport.
 
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