Runaway Voltage

[millsmobile]

I'm still having trouble with the charging system on my 79 CB750. Right now it's got a brand new rotor, brand new stator, and brand new regulator/rectifier. It has a pretty new Shorai lithium battery that is taking a charge and seems to be fine. I'm finally able to get voltage out of it, but after a few minutes of riding the voltage runs away. I was in the low 13's and idle, mid 14's revved, and then it would quickly escalate to 15, 16... pretty sure I saw a 19 on there before the M-Unit shut it down. The system was previous working and holding steady 14.8v regardless of RPM before the rotor went bad taking some other stuff with it. Please help!

 

[mrtwowheel]

What are you using for a regulator?

 

[brettp]

The regulator is responsible for limiting that voltage to the battery. If you bought cheap Chineseum, that is likely it.
Question, after you see that voltage spiking, does it reset after killing the bike?

 

[millsmobile]

The regulator is responsible for limiting that voltage to the battery. If you bought cheap Chineseum, that is likely it.
Question, after you see that voltage spiking, does it reset after killing the bike?

Everything except the stator is Rick's. After the bike shut down the voltage was still really high, like 15v + and then it started dropping. After starting it quickly did the same thing, like the battery was full and it wouldn't stop charging it. Was able to unplug the white and black from the regulator to ride it home.

 

[brettp]

I'm not an expert in the electrical side of things, but can a lithium battery "demand" more from a R/R? My intuition says no, but again, I'm not an expert.

 

[kirky]

my twopenneth i don't think it is advisable to charge a lithium battery with a conventional lead acid battery charger, and maybe not on a motorcycle that was fitted with a lead acid battery. i also think lithium battery's can run away when being charged , hence loads of them catching fire

 

[brettp]

I wish I knew more about that conversion and what is required to be changed. I've read of new R/Rs needed, then also read some lithium batteries have internal protection. Lots of variables.

 

[Loose Chain]

Everything except the stator is Rick's. After the bike shut down the voltage was still really high, like 15v + and then it started dropping. After starting it quickly did the same thing, like the battery was full and it wouldn't stop charging it. Was able to unplug the white and black from the regulator to ride it home.

Don't assume because it is new that it can't be the problem. Your regulator should able to control the amount of charge. Double check that the regulator is connected correctly. I'm old school when it comes "updating" old bikes. I still use acid filled batteries in all my bikes and have zero issues with any of them.

 

[millsmobile]

So I discovered a pretty interesting wiring snafu that may or may not have been responsible for a lot of these issues I've been having. Previous owner had the key/ignition wire powering the M-Unit, when that wire is supposed to go to the lock input and the M-Unit is connected directly to 12v via the battery. Based on my other post with voltage issues and the tech I spoke to at Ricks, the regulator/rectifier has two wires that go to the battery. One is switched 12v power, and the other is the output from the regulator. It regulates by comparing the two voltages. It was previously suggested that the switch iteself could be a culprit and cause a voltage drop (it's been replaced), but surely not that big. A 1v drop would give a 1v boost from the regulator output. With all the power for the M-Unit and everything else on the bike going through that key switch, who knows. Anyway, fixed that wiring today following the M-Unit diagram. I did not experience any over voltage on a short test ride, however it did blow the 20A fuse that was in there. Pretty sure it's supposed to be 30 or 40. The bike previously had 2 20A fuses, one in the starter solenoid, and one between battery and the ignition switch.

Don't assume because it is new that it can't be the problem. Your regulator should able to control the amount of charge. Double check that the regulator is connected correctly. I'm old school when it comes "updating" old bikes. I still use acid filled batteries in all my bikes and have zero issues with any of them.

Getting pretty close to slapping the AGM battery back in there just to see. I went lithium because the bike was chewing through the lead batteries faster than I could get it started, but it's starting really quick now so might be worth testing. It did previously work with the lithium battery and held rock solid voltage until the rotor failed.

I'm not an expert in the electrical side of things, but can a lithium battery "demand" more from a R/R? My intuition says no, but again, I'm not an expert.

I don't think so. It reads about 13.2V when fully charged so it's not much higher, and according the spec sheet it can handle up to 15.2V to charge which makes it compatible with either regulator.

 

[millsmobile]

So I rechecked all wiring, installed the proper fuses, and no charging at all. Took the cover off and the brand new rotor is completely burnt. Like melted plastic everywhere burnt. I'm working with a tech at Rick's to figure out wtf.

Obviously I know it won't charge, but can I ride this thing without the rotor or is it needed to balance the engine?

 

[brettp]

It is needed to provide electricity to the spark plugs, etc. Without it, your battery does all the work and dies quickly

 

[millsmobile]

It is needed to provide electricity to the spark plugs, etc. Without it, your battery does all the work and dies quickly

Yah I'm familiar with that program haha. Shockingly the ignition draws the least amount of power, the headlight is the hog. While working on this I've discovered I get about 30 miles on the battery with the light on before it dies lol. I'm just curious if it's safe for the engine.

 

[brettp]

I can't think of any reason it would be detrimental to the engine. Don't leave your blinkers on, though. You'll probably only get 29.5!