OT Zener diode rating

[topct]

I am figuring out the wiring for a little motorcycle I am building.

I do not want to use a battery, however the original setup used one as a voltage regulator to prevent the charging system from blowing the lights.

How can I figure out what size zener to put in the curcuit to keep this from happening.

The lights and ignition are 6 volt. The ignition is not a concern. The motor starts and runs just fine without a battery. It's when you turn on the lights and rev the motor that takes the lights out.

The headlight is rated at 25watts low beam and 35 high beam. I'm guessing the tail light to be about 5?



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Gene

[Evan]

Instead of just a zener diode make a simple shunt regulator. Then you can use any zener available, the wattage won't matter as long as it is good for a watt or so. The power transistor is any npn low frequency type like a 2N3055 or equivalent on a small heat sink. The resistor is 1/2 watt.





[This message has been edited by Evan (edited 12-27-2005).]

[Lew Hartswick]

Evan, I've been out of the "game" for 8 yrs
now but I would think one of the TO 220 regs.
would be easier to impliment for this req.
...lew...

[Evan]

Not enough watts. Also, if they get too hot they go into foldback current limit and your lights go out. The 2N3055 can take around 100 watts on a heat sink.

[Mcgyver]

Evan, wondering whether you need a current limiting resistor on the base?

[topct]

Evan, you show an 8 or 14 volt zener. For a 6 volt system am I right in assumming the 8 volt would be the one to use?

These little Hondas use a sealed beam headlight and they go for about $50. Without a battery to control the output of the alternator they let go at the first blip of the throttle. The tail light goes as soon as you turn the lights on, at idle.

Just trying to save that headlight.

[Evan]

I changed the schematic, see above. I had the wrong one. As for current limit on the base the zener will act as a current limiter. That's why the zener by itself isn't that good since it has significant avalanche resistance.

For a 6 volt system use the 8 volt zener. That isn't critical, anything from about 6 to 8.5 volts should work ok.

[This message has been edited by Evan (edited 12-27-2005).]

[topct]

Evan, what type of cap would that 10uf be?

[Evan]

Any small electrolytic (polarised) capacitor with a voltage rating of maybe 16v or higher. It's there along with the resistor to provide a small amount of filtering action. The value is totally non critical and can be anything from 10 to 100 mfd.

[topct]

Thanks for the help Evan. When the weather clears I'll fire it up and see what happens.

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Gene