1982 CB125 running 50vs to the headlight?

Highwind

New Member
my mechanic said that the bike was running 50volts to the headlight and would not want to put one in till I fixed it. He said it might be a bad regulator (and I agree) is it possible to just switch out the regulator with a rectifier? The thing is the taillight is running fine (is it AC to DC or DC to AC for 6volts "forgot")
 
The stator outputs and un-rectified AC signal, meaning you'll have both positive and negative voltages going into the electrical system. When you add a rectifier it uses clever placement of diodes to turn the negative AC voltage into positive AC voltage. It will still at this point be much higher than 6v. The regulator will not allow the rectified output to go above a set voltage. In the case of 6V systems this limit is 6V. I made a diagram in paint which illustrates this.

As far as the CB125 electrical systems, there is no regulator. There is only a selenium rectifier. It is likely this is your problem. You can and should replace this with a Radioshack full-bridge wave rectifier. They're about $5. The 6V battery on the CB125 acts as the regulator. If you want a regulator something like this https://www.treatland.tv/6-volt-voltage-regulator-p/6v-voltage-regulator.htm will work.
 

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1982 CB125 running 50vs to the headlight?

20130902_130459_zps6a582202.jpg


Top is my 1982 cb125 regulator
Middle is my new regulator
Bottom is my 1979 cb125 regulator

Why does my 82 have two extra wires (pink and yellow)


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The stator has two windings. One supplies power for the spark/ignition system, the other supplies power for the lights. Attached is a wiring diagram for a CB125S.
 

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Your diagram of A/C, Rectified, regulated is a little wring. The A/C and rectified is right. There is no regulator, and models with a regulator have no capacitors to smooth out the DC anyway.

These little bikes rely on the battery to smooth the DC and the alternator has just enough current to keep up. No regulator at all. A regulator can be added. The type of regulator for these does not adjust the output at all, though. The output from the alternator is current, and it has a fixed ratio of current to RPM.

The regulator is a variable shunt to ground, that, when the voltage exceeds 15V, the regulator just adds a load to maintain the 15V. It is merely a limiter, rather than a full fledged regulator. Alternators with variable field coils actually adjust the output of the alternator to match the load. Permanent magnet alternators have a fixed strength field so output regulation can;t happen, only load can be varied to keep the volts down.
 
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