High Voltage "cure"?

[Tim Allman]

I've noted before on my restore threads that both my CA77 and CL77 run high voltage. At road speed any where from 16.8 to 17.1 volts, depending on the meter used (not expensive ones obviously.)

According to my experience and my shop manual, your voltage is just fine. It should be about 12 V at idle and be discharging the battery. It climbs to a maximum of about 17 V at 3500 rpm and supplies about 1.5 to 2 A to the battery. Both lights on and lights off states have similar characteristics because the output from the alternator is doubled when the lights are turned on.

Diane,
I agree with your comments. I made a replacement bridge rectifier from four top hat Si diodes, some aluminium plates and the hardware from my disassembled Se rectifier many years ago because of charging issues. It doesn't change the voltage curve much but the peak charging current is increased by ~0.5 A and the new rectifier runs cooler than the old one, presumably because of the decreased forward resistance. This setup is sufficient and I have never found a need to add a regulator although any added electric accessories such as the electronic ignition described on this site might well tax the system.

[OldStan]

I'm not sure on a stock CA77 headlight, but on mine there is also a 13 watt difference.

Haven't done any measurements on mine, but the C77 wiring diagram shows 35 watts for both hi and lo beam?

That's what I thought I'd seen somewhere. My bulb burned out and I adapted a 25/35 watt bulb which is the same wattage as the CL77 is stock. Probably shouldn't have, but that is what I found. I'm not sure why it's different but it certainly would unbalance the system.

[OldStan]

If you are using a Zener diode for regulating voltage, there MUST be a resistance between the voltage source (the stator) and the Zener because the Zener acts as a voltage clamp and will divert as much current to ground as it has to to maintain voltage. If you don't add resistance, you may overheat your stator. All of the energy that is "dumped" is wasted as heat.

I understand it is dumping the energy as heat, that is why I'm using a heat sink. Adding a resistor prior to the Zener would be dumping some of the heat there. Wouldn't that change the voltage that the Zener is sensing? Back when I was an electrician in the service we would install resistors to run 12 volt accessories on a 24 volt system, the resistor size being dependent on the load. Off hand I'm not sure how this would relate to the Zener sensing voltage.

If Honda designed this as a balanced system, we have unbalanced it with the silicone diodes in the rectifier when we made the system more efficient. In my initial testing the Zener was drawing .5 to .6 amps at high RPM with the lights on high beam. I have installed the Zener so that any current runs through the main fuse.

We're not working with a system comparable to a modern automotive alternator which is capable of putting out high amperage at low rpm. Since the British bikes use the Zener with a heat sink on a comparable system I'd think it should be a workable solution. I know there are better systems out there, just trying a low cost alternative. I could be proven wrong, wouldn't be the first time.

[G-Man]

Oldstan

I agree. Because the alternator is not a constant voltage source whatever you do the excess energy must end up as heat. If you increase the resistance on the output, then the voltage will rise on the AC side and this may be what Dianne is getting at. If we can tolerate the extra AC volts then that might work.

I think that the Podtronics units are just bridge rectifier and Zener in one package.

G

If you are using a Zener diode for regulating voltage, there MUST be a resistance between the voltage source (the stator) and the Zener because the Zener acts as a voltage clamp and will divert as much current to ground as it has to to maintain voltage. If you don't add resistance, you may overheat your stator. All of the energy that is "dumped" is wasted as heat.

I understand it is dumping the energy as heat, that is why I'm using a heat sink. Adding a resistor prior to the Zener would be dumping some of the heat there. Wouldn't that change the voltage that the Zener is sensing? Back when I was an electrician in the service we would install resistors to run 12 volt accessories on a 24 volt system, the resistor size being dependent on the load. Off hand I'm not sure how this would relate to the Zener sensing voltage.

If Honda designed this as a balanced system, we have unbalanced it with the silicone diodes in the rectifier when we made the system more efficient. In my initial testing the Zener was drawing .5 to .6 amps at high RPM with the lights on high beam. I have installed the Zener so that any current runs through the main fuse.

We're not working with a system comparable to a modern automotive alternator which is capable of putting out high amperage at low rpm. Since the British bikes use the Zener with a heat sink on a comparable system I'd think it should be a workable solution. I know there are better systems out there, just trying a low cost alternative. I could be proven wrong, wouldn't be the first time.

[DianneB]

I understand it is dumping the energy as heat, that is why I'm using a heat sink. Adding a resistor prior to the Zener would be dumping some of the heat there. Wouldn't that change the voltage that the Zener is sensing?

No, it wouldn't. The Zener diode operates as a voltage clamp. At any voltage below the Zener voltage, the Zener diode does nothing - it's like it isn't even there. But, as the voltage tries to rise ABOVE the Zener voltage, the diode will dump as much current to ground as it has to to maintain the Zener voltage - up to the point where the Zener diode melts - which is exactly what would happen if there was no resistance in the supply circuit.

If you don't add a resistor in the supply circuit, the resistance of your stator will perform that function and the heat will be dissipated in the stator. That may or may not damage your stator. If the stator were wound with heavy wire, either it will fail or you Zener will fail.

If Honda designed this as a balanced system, we have unbalanced it with the silicone diodes in the rectifier when we made the system more efficient.

It was never "balanced". Honda designed the charging system with "the technology of the day" and would have boosted the stator voltage to get the charging current they wanted through the higher resistance of the Selenium rectifiers.

[OldStan]

Here's how Triumph did it on the late 60's.

[G-Man]

This is a conversion I did on a 1950s BSA Bantam. I converted the 6v 'direct' system to 12v, added the Zener Diode, bridge rectifier and a 12v battery to give me some nice bright lights, even at tickover. This was about 20 years ago....



All of the extra bits were hidden under the tank so that it didn't spoil the look of the bike.





G