PS on one of the yamaha xt500 sites people have done the change to 12 v (there are plenty of volts) but you need to unsolder the ground (and resolder a wire)for full wave rectification.

if the regulator is hooked up to the low current wire that regulates the high current as well (they are on the same coil)

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You could try to use those modern PWM controlled Solar charge regulators. They are very efficient andle currents up to 30A. Just use a bridge rectifies and capacitor to filter the input.

 

Do you have any plans or circuits? could they handle 130v?

 

Remember, 130V is "no-load" voltage. Try to connect 100W lamp and you never reach 130V. The regulators are no so expensive. You can google for switchmode regulators. These are good and efficient too. I have some circuits for these but only up to 3A.

 

I realise that it is all a bit acedemic, as you don't have the bike, but winding the alternator for a higher voltage would have been counterproductive.

Twice the turns would mean twice the voltage, but 4 times the inductance, so half the current, and exactly the same amount of power......

I found that just changing to a higher voltage bulb of the same current worked well, although the dimming at tickover was worse. The self regulating feature of the coils kept the current the same as before at high revs.

 

All that sounds like fun but i don't think my xt 500 has a self regulating coil. i have blown 4 bulbs in a week and a half and they are hard to find now 25 years later. for the moment i have a very crude regulator that stops my battery boiling. a triac shorts the coil triggered by two zener diode in series anode together. my scope tells me it works a bit but it is too crude.

no body has better ideas?

scr are used in industry regulators but i have no idea how to use them in a shunt circuit.

i would like to ride my motorbike after dark and sleep at night.

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Yes, but you only need half the current anyway - that's the point of moving to 12V.

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OK if we talk coils: has anybody made a model of a single phase magneto (eg LTspice)? on my scope i have 4 phases per rpm. It would be cool to model a rewire of the coil.

 

I thought the idea of moving to 12 V was to get more power.

Lower voltage filaments are better because they are fatter and can be run hotter, so unless you can get more power by going to 12 V you will end up slightly worse off.

12 V is generally better in a car because the currents are lower so the voltage drops are much less significant.

 

A note about magneto generators. Some comercial diesel engines use magneto generators to charge the battery. To regulate the output, a second winding is wound over the main AC winding. The regulator has 2 sections: bridge rectifier from the main winding to the battery, the second part "injects" a dc voltage into the second winding "counteracting" the magnetic field. The greater the DC the lower the AC.

 

No, it's to improve the brightness of the lights, by reducing losses.

That's the exact same reason to use 12V on a bike as well.

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Has your bike got a directly lit headlight? If so, you are best to shunt it with a resistor to keep the voltage down to the rated voltage for the bulb.

 

Not a very good plan! - the headlight is already very poor at low revs, so adding an extra load is going to make it worse.

Like I said before, I used to have a DT400, and I never had to replace the headlight bulb at all - and it had a LOT of use, it was my sole mode of transport for a number of years.

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no, the reason to move to 12v is to use the power that is already produced (135w). the light bulb i have is a 35W. 12V light bulbs use 45w or 55w. the bike was made with a regulator.

i have found a circuit on the net that uses a triac but when i try to model it in spice it regulates at 2 volts (and only without a capacitor). could anybody have a look to see if there is an error.

The coil produces enough power, other people have already done this with a regulator for a skidoo (snow bike). the circuit below is supposed to be be the same. if you speak French i can give you the site where people explained what they have done.

can we presume that the coil (the V,the I and so the power) will be at the end of the wires. all i need is a good regulator.

this is the 3rd circuit i have posted. triac, scr, or transistor can nobody help me? (please)

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i would like to try to regulate before rewinding the coil.