NGC 72 CB 750 chopper charging problem

[bobrebos]

Been working on my old 1972 Honda CB 750 Chopper (SOHC).  On Wednesday I’m going to install a solid state voltage regulator in place of the original non solid state one to see if I can get it to quit charging at 15.6volts at about 3500rpm.  It should be charging around 14volts only not 15.6!

[nc43bsa]

I know it's hard to believe, but it's a 50 year old Honda.

You sure those electrons haven't been taking Viagra?

[bobrebos]

I know it's hard to believe, but it's a 50 year old Honda.

You sure those electrons haven't been taking Viagra?

Those electrons have been taking SOMETHING!

[Tom]

Is the old voltage regulator adjustable?  Just asking.  Maybe add an inline capacitor/resistor?  Have to have an electrical guy pipe in.  Yeah 15v is too hot. 

[Redrider]

Fully charged LA battery cells are 2.34 v/cell times 6 cells =14.04 so your 15 volts may be the accepted norm for back then. Most folks have the belief that the system is 12 volt because that is how it is marketed. Are you blowing bulbs?

[bobrebos]

Is the old voltage regulator adjustable?  Just asking.  Maybe add an inline capacitor/resistor?  Have to have an electrical guy pipe in.  Yeah 15v is too hot. 

Yes the original regulators are adjustable but I thought I’d try a solid state one first.  If that doesn’t work Il try to figure out how to adjust the original one.

[yogidozer]

Looks like my old bike. Looked through my old stuff, couldn't find anything.
Try this test
How do you test a solid state regulator?
Image result for 1972 honda 750 solid state voltage regulator overcharging battery
To check the regulator, proceed as follows.
Remove the regulator.
Measure resistance between the brown and black leads (Figure 31). Resistance should be approximately 55 ohms.
Connect a voltmeter across the battery terminals. Reconnect the regulator.
Start the engine and run it at 5,000 rpm.

[bobrebos]

Fully charged LA battery cells are 2.34 v/cell times 6 cells =14.04 so your 15 volts may be the accepted norm for back then. Most folks have the belief that the system is 12 volt because that is how it is marketed. Are you blowing bulbs?

No I am not blowing any bulbs

[Navydad]

All of the BIG FOUR motorcycle companies had charging issues in the early and mid 70's, but Honda and Kawasaki were the worst. I rewound many stators and replaced many regulator\rectifiers during those years. If the stator is good then a new regulator\rectifier will do the trick. Don't even waste your time trying to adjust or tinker with the old one. They were junk. There is a forum that is specifically in existence for the SOHC Hondas. A wealth of information there. I will try to find it and list it here. I recently restored a 1981 Suzuki 850, another bike with a crap charging system. Used a modern regulator\rectifier from Polaris. Works great.

http://forums.sohc4.net/

[bobrebos]

All of the BIG FOUR motorcycle companies had charging issues in the early and mid 70's, but Honda and Kawasaki were the worst. I rewound many stators and replaced many regulator\rectifiers during those years. If the stator is good then a new regulator\rectifier will do the trick. Don't even waste your time trying to adjust or tinker with the old one. They were junk. There is a forum that is specifically in existence for the SOHC Hondas. A wealth of information there. I will try to find it and list it here. I recently restored a 1981 Suzuki 850, another bike with a crap charging system. Used a modern regulator\rectifier from Polaris. Works great.

http://forums.sohc4.net/

I don’t know why it’s overcharging at a high rpm (15.6 volts) but I’m hoping it’s the voltage regulator problem and the solid state replacement one will work.  Don’t know what affect a bad stator would have on it?  Could that cause it to charge at a high rate?  Thanks

[Redrider]

I have a schematic and service manual in the archives for the stock configuration. Will dig them out.

[Old Jock]

Just an obvious suggestion, have you checked the earth connections and the regulator reference connection?

I'd make sure the reference connections were clean and tight.

If the ref connection has resistance then the regulator will "think" the system voltage is lower than it actually is, resulting in a higher charging voltage

You probably already know that but it's usually a reasonably easy thing to do

[bobrebos]

Just an obvious suggestion, have you checked the earth connections and the regulator reference connection?

I'd make sure the reference connections were clean and tight.

If the ref connection has resistance then the regulator will "think" the system voltage is lower than it actually is, resulting in a higher charging voltage

You probably already know that but it's usually a reasonably easy thing to do

Good point and Il check connections out. 

[larrys]

Does your chopper have a custom wiring harness or was the stock harness modified and used? Checking for bad grounds is always a good first step in troubleshooting electrical gremlins. Back when folks chopped everything, I had a side gig going making custom harnesses for choppers. Did many HD's, Brits, and a few Jap bikes.
Larry

[guzziart]

Just an obvious suggestion, have you checked the earth connections and the regulator reference connection?

I'd make sure the reference connections were clean and tight.

If the ref connection has resistance then the regulator will "think" the system voltage is lower than it actually is, resulting in a higher charging voltage

You probably already know that but it's usually a reasonably easy thing to do

 

[bobrebos]

Installed a solid state voltage regulator.  Charging voltage at like 4000rpm is 14.8 compared to what it was at 15.6 volts.  I wonder if 14.8 is still too high???? Hmmmm????  And of course I found a loose exhaust pipe while working on it.  Might explain some popping I’ve been having.  Always something with these old bikes! 

[Redrider]

Not really. It needs to be higher than the no load battery voltage so the current will flow into the battery. You will need to keep an eye on electrolyte level. When the battery reaches 80% charge, it starts to outgas-breaking water into H and O2. Only add water after the 80% point otherwise the battery may overflow. If you see the plates exposed at the beginning, only add enough water to cover the plates NOT to the minimum level mark.

[Navydad]

14.8 is good. Your stator is good. The reason I mentioned the stator is because it was an issue with bikes of that era and the first thing I checked. Vibration and heat would break down the insulation, what little of it there was, and the stator would short out. Common problem back then. The early 1200 Goldwings were a good example of that, it was so bad Honda was replacing them under warranty. Make sure all of your electrical connections are clean and tight as those old systems won't tolerate much variance in amperage. The new regulator/rectifier will help with that issue, but it's still an old system. Sounds like you have it sorted out, but keep an eye on your battery anyway.

[bobrebos]

14.8 is good. Your stator is good. The reason I mentioned the stator is because it was an issue with bikes of that era and the first thing I checked. Vibration and heat would break down the insulation, what little of it there was, and the stator would short out. Common problem back then. The early 1200 Goldwings were a good example of that, it was so bad Honda was replacing them under warranty. Make sure all of your electrical connections are clean and tight as those old systems won't tolerate much variance in amperage. The new regulator/rectifier will help with that issue, but it's still an old system. Sounds like you have it sorted out, but keep an eye on your battery anyway.

Thank You

[John A]

In the old Delco Remy o/h manual it says if the customer complains the battery uses too much water, adjust the regulator down a little but that was only up to about the 60’s. Same thing here I expect