Topic: Battery dying intermittently

[bagatyr]

I've got a bit of a strange problem with my battery or charging system.

I recently got this bike, Honda cb750 78, running, rewired it completely, rebuilt carbs thrice, 3000mile tune up. It runs great! It's got an 836cc kit in it, mUnit and a antigravity battery. I couldn't have done this without the forum so many thanks all around. Especially Cal.
Now, moving on to my problem. The bike doesn't have a parasitic drain, but it will be running fine and then all of a sudden stop charging. I thought my R/R was too hot. But I just felt it and it was cool. The air temp is in the 60s and I was going over 40mph when I heard "Voltage Low" over my earpiece. The only thing I have on is a light, and it's a modern led so it doesn't draw much power.
It can ride around town and it seems fine, but I've had it discharge on me when I've started riding faster than city speeds..is it a vibration issue? Something loose? I checked the battery bolts and they were nice and tight, so are the bolts on the mUnit and ground strap.
If the R/R fried then it wouldn't charge normally the other half of the time.
Is it my alternator? Maybe it's loose and disengages at a high RPM?

 Is there a good post on checking my charging system that someone could point me to

Thanks for all the help!

[Don R]

 My brothers 76 wing had an intermittent bad battery. Just a thought.

[bagatyr]

How would I diagnose that? Just a load test at an AutoZone or something?

After charging the battery rests at 13.4 which is in spec.

It seems like it has something to do with heat. Only a problem after the bike is nice and hot. The battery itself doesn't get hot. I'll try cleaning the connections from the alternator, those wires are getting baked down there.

[scottly]

I was going over 40mph when I heard "Voltage Low" over my earpiece.

Is the voice in your head the only symptom? What is the voltage at the battery with the motor running?

[maxheadflow]

Assuming all the connections are good between the alternator and rectifier, it's possible that you have a heat related short to ground in alternator. It can be hard to troubleshoot as it only occurs at higher temps.  Back in the late 70s I worked on a CB750A police bike that would do this.  It was a PITA to find.  The officer was sitting for periods of time with the motor idling while another had a radar gun.  We put a fan on the motor so it didn't get too hot and set a high idle. After some period, the bike quit charging. Replacing the stator windings fixed the problem.

[bagatyr]

Got a load test at Oreillys, battery is bad. This is the best news. Glad it wasn't my stator or a heat short. Thanks for your help guys.
Battery is an Antigravity 8 cell. It's been used for a handful of rides. Must have been defective from manufacturer.