High Voltage "cure"?

OldStan · Post by **OldStan** » Fri Jul 24, 2015 6:05 pm

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.) I have the Classic Honda silicon diode rectifier on both bikes already. I decided to do some experimenting. I've installed voltmeters on both bikes, these meters both read max of 16.8 volts. I did some research on zener diodes, which have been mentioned on this forum a few times. In the day they were used on some of the British bikes so I figured it was worth a try. I obtained a 14v 50 watt zener diode for each bike. These I installed on an aluminum plate for a heat sink (using dielectric grease) and suspended them in the headlight shell on high temp silicone. They are both wired in so they are keyed off. So far I've logged 100+ miles on the CA77 and 250+ miles on the CL77 in about 50 mile stretches between shutoffs, no city driving. Now the max voltage is 14.8 volts. All driving was with the headlights on high beam. Now it's just a matter of seeing how long they last. I think at worst they'll just burn out and I'll be back where I started.

brewsky · Post by **brewsky** » Fri Jul 24, 2015 7:54 pm

Wonder what adding some driving lights would do to soak up some of the extra juice?

OldStan · Post by **OldStan** » Fri Jul 24, 2015 11:39 pm

I thought about that. If you were driving in traffic you would have to turn them off to prevent battery drain, a particular problem on the CL77 with it's 2ah battery. With the zener diode there is no draw when you are below 14 volt (+ or - 5%). Sizing (wattage) could be a problem. High beam to low beam there is a 13 watt difference (10 on the light, 3 on the high beam indicator) on the CL77. I'm not sure on a stock CA77 headlight, but on mine there is also a 13 watt difference.

DianneB · Post by **DianneB** » Sat Jul 25, 2015 4:52 am

I am working on a '67 C77 and just replaced the Selenium bridge with a Silicon bridge rectifier on my bike. I am a retired electronics designer and know that Silicon is a much more efficient rectifier - it has much lower forward voltage drop (when conducting) and very little resistance in the conducting direction compared to a Selenium bridge. I have not started my bike yet (but will very soon) and will have to check the voltage when charging. Anything over 14 volts will shorten battery life; ideal would be 13.6 volts.

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.

A much better approach would be to use a "3 terminal regulator" with an output voltage of 13.6 volts because a 3-terminal regulator only PASSES enough energy to maintain the output voltage. The only wasted energy is the difference between input voltage and output voltage (multiplied by the current). A 3-terminal regulator will maintain the 13.6 volt output as long as the stator is producing a voltage above 13.6 - this is the exact arrangement used in an automotive alternator.

There are two types of regulators - linear and digital. Linear regulators maintain voltage like a variable resistance and dissipate excess energy as heat. A digital (or "switching regulator") dissipates far less heat and behaves as a switch, turning on and off very rapidly to maintain output voltage and are therefore FAR more efficient.

I haven't reach that point in my project bike yet so I haven't looked at what is available in the electronics market yet but I will be doing that soon. I will keep you posted.

brewsky · Post by **brewsky** » Sat Jul 25, 2015 7:16 am

OldStan wrote: 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?

G-Man · Post by **G-Man** » Sat Jul 25, 2015 8:17 am

Hi Dianne

I'll be interested to see your findings. I thought that automotive and later motorcycle regulators worked by reducing the field current to the alternator and therefore controlling the power at source.

I'm interested to know where the excess energy goes with your three-wire regulator. Is that what Podtronics use in these? http://www.podtronics.net/DC_regulator.htm

The usual 'control' with the Honda alternator and most early Lucas systems was to switch in extra coils as you upped the load (usually the lights)

G

DianneB wrote:I am working on a '67 C77 and just replaced the Selenium bridge with a Silicon bridge rectifier on my bike. I am a retired electronics designer and know that Silicon is a much more efficient rectifier - it has much lower forward voltage drop (when conducting) and very little resistance in the conducting direction compared to a Selenium bridge. I have not started my bike yet (but will very soon) and will have to check the voltage when charging. Anything over 14 volts will shorten battery life; ideal would be 13.6 volts.

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.

A much better approach would be to use a "3 terminal regulator" with an output voltage of 13.6 volts because a 3-terminal regulator only PASSES enough energy to maintain the output voltage. The only wasted energy is the difference between input voltage and output voltage (multiplied by the current). A 3-terminal regulator will maintain the 13.6 volt output as long as the stator is producing a voltage above 13.6 - this is the exact arrangement used in an automotive alternator.

There are two types of regulators - linear and digital. Linear regulators maintain voltage like a variable resistance and dissipate excess energy as heat. A digital (or "switching regulator") dissipates far less heat and behaves as a switch, turning on and off very rapidly to maintain output voltage and are therefore FAR more efficient.

I haven't reach that point in my project bike yet so I haven't looked at what is available in the electronics market yet but I will be doing that soon. I will keep you posted.

DianneB · Post by **DianneB** » Sat Jul 25, 2015 1:13 pm

Many of the early alternators made some attempt to use the field to control the output voltage and many large generators (like Kilowatt size and bigger) still do. Large alternators like trucks and buses do as well to save power but with the advances in solid state electronics the automotive alternators I have seen in the last decade or so just run the field 'wide open' and regulate the output. Many small AC generators are using permanent magnet armatures and turning the resulting AC into DC and then back to AC at 60 Hz and regulating the output all with electronics.