CB750 overcharging

[rocks]

Hi there,

This is a 1975 CB750F SuperSport

So I got Rick's rectifier/regulator combo, and now the battery is overcharging. Pass 15v at 4000rpm. I cleaned all connector, and still the same. I bought new handlebar controllers and ignition switch, but no luck (old once looked old and cracked). I took the harness apart. Removed the old wrap. Inspected every wire, cleaned connector again, and it still the same. I put HID xenon bulb with 35W, but didn't do much.

The battery is fairly new and fully charged. The thing that I don't get is when I connect the black wire straight from regulator to the positive(+) battery it charges perfectly at 14.5v.

Does this mean that I don't have issues with my stator?

I know I can't leave it connected that way, but what would be a solution for this?

The black wire starts from the ignition switch to front brake switch, starter switch, engine stop switch, winker relay, oil pressure light, neutral light, turn signal buzzer, horn, rear brake switch and then to the Regulator.

Will it work if I go from ignition switch straight to + battery?

Thank you

 

[hillsy]

The thing that I don't get is when I connect the black wire straight from regulator to the positive(+) battery it charges perfectly at 14.5v.

I know I can't leave it connected that way, but what would be a solution for this?

If you put a 30A fuse in line you can connect the charging wire directly to the battery. Quite common to do this on a lot of bikes.

 

[Bert Jan]

On old Honda bikes, the black wire IS positive when ignition is in "ON" position. The black wire from the regulator is in the system so the regulator knows how much power is drawn from the system and how much is needed. The regulator checks battery voltage and power consumption. The difference in those two is then made up by giving the field coil less or more juice to generate power to the stator. The reg/rec also has a red wire which goes onto the positive terminal of the battery. I'm not sure but by putting black and red both on the battery terminal i guess you'll damage the reg/rec..

When you connect the black wire from the regulator direct to the battery but not into the loom, the regulator will go for the best option as it has no idea how much power is drawn. The best option is to give a nice and steady 14.5v

As i don't know how the setup was before you put the black direclty on the battery i cannot help you further. Please elaborate how you connected the reg/rec. succes!

 

[rocks]

On old Honda bikes, the black wire IS positive when ignition is in "ON" position. The black wire from the regulator is in the system so the regulator knows how much power is drawn from the system and how much is needed. The regulator checks battery voltage and power consumption. The difference in those two is then made up by giving the field coil less or more juice to generate power to the stator. The reg/rec also has a red wire which goes onto the positive terminal of the battery. I'm not sure but by putting black and red both on the battery terminal i guess you'll damage the reg/rec..

When you connect the black wire from the regulator direct to the battery but not into the loom, the regulator will go for the best option as it has no idea how much power is drawn. The best option is to give a nice and steady 14.5v

As i don't know how the setup was before you put the black direclty on the battery i cannot help you further. Please elaborate how you connected the reg/rec. succes!

I did not change the wiring setup. The new R/R I got is a plug and play. The red and black are both connected to + battery. At higher rpm the regulator most of the time puts out around 14.5v. So I figured connecting it straight to the + battery would be better.
But, when the bike is off, am sure the system will drain the battery unless if I put a diode in there, but I really don't want band aids. So, I am still looking what's causing it. The stock reg works fine.

 

[Sonreir]

The battery is fairly new and fully charged. The thing that I don't get is when I connect the black wire straight from regulator to the positive(+) battery it charges perfectly at 14.5v.

The black wire is the voltage input for the R/R and is used to "sense" the voltage in your system. As bikes and wires get older, resistance can build up (in the form of corrosion, mostly) within the wires and connectors. This increased resistance in the circuit means your voltage sensing wire is "seeing" less voltage than is actually present. When you bypass the old wiring and run it directly from the battery positive terminal, the black wire sees the correct voltage and everything works as expected.

You can still do (and should do) this bypass, but you'll want a relay so you don't drain the battery when the bike is off.

Find yourself a four or five pin automotive relay good for at least 10A and also grab yourself an inline fuse and stick at 10A fuse into it.

Connect the fuse holder to the battery positive terminal and the other end of the fuse holder to pin 30 on the relay. Pin 87 should connect to the black wire on the r/r. Pin 85 goes to the black wire where you previously plugged in the r/r, and pin 86 gets grounded.

This will give you a good solid connection from the battery to the r/r, but only when the ignition switch is turned on.

 

[conraderb]

2+ years later, I just wanted to give a giant thanks to Sonreir about the relay idea!

I have a Nighthawk CB700SC that was overcharging due to a voltage drop on the black signal wire.

I bought a Rick's Motorsports R/R, but the problem persisted!

I was a bit intimidated by dealing with a relay, but Sonreir's instructions made sense, and after $10 for relay and some careful soldering, the problem is solved.

My bike makes a satisfying click sound when I turn the key

I'm surprised that other forums don't post information about doing a relay mod to deal with this - I would presume that it is quite common on older motorcycles, right??

 

[Sonreir]

Right on.