6 Vac to 6 Vdc rectifier /regulator for a motorcycle

If the magneto has an isolated winding, a simple bridge rectifier may be all you need to convert the output to DC. You might use one made of Schottky diodes to cut the need for heat sinking in half. I think that regulators for such systems are often simple shunt regulators that load the battery voltage to keep it from exceeding about 7 volts. These are rather simple zener diode transistor circuits. But they need to be switched off when not in use, if connected directly across the battery. If they have their own bridge rectifier, so they load only the magneto coil, that bridge isolates them from the battery when the engine is off.

Heyyy...I thought Si diodes generally have less Vd than Schottky? The less Vd..the less Pdisp. D from BC

Have you actually looked at this? I thought the magneto put out several thousand volts to fire the spark plug. Where does the battery come from?

Tam

It can also provide power for lighting as well as battery charging and ignition.

A Schottky diode is something like a half of a semiconductor junction (metal taking the place of the N type material). They generally have about half the forward drop of full junctions, and also have low reverse voltage ratings and high reverse leakage current.

Here are a couple data sheets for you to compare.

Dohhh! :( Dunno how I got that mixed up.. Time for another coffee! I looked at the datasheets. Even around the 10A point the schottky Vd wins at 25C. Thanks for the correction.. Also good for the news achieves. I'll try to be more careful..

D from BC

I remember the use of selenium rectifiers! man did those stink when over heated.

Exactly; their leakage is as bad as that of Germanium diodes, withessentially the same forward drop.

(snip)

I wonder if anyone makes a germanium Schottky. It should have something like a 50 mV forward drop and be good for a couple volts, reverse.

Why not a power MOSFET and a comparator to switch it? At low frequencies it's pretty easy to do.

...Jim Thompson

Thank you, John. This is the first time I've heard it described so concisely. :-)

Thanks! Rich

Hey! We should ask Jim Thompson - he designs IC's; he must have some kind of contact with the people that operate the foundry. :-)

Cheers! Rich

Do you have contact with the foundry people? Do you specify materials for your epitaxials? A gremanium Schottky sounds like just the ticket, in these days of Vcc l of a volt or so.

Cheers! Rich

One of the transmitters I worked on in the USAF had a separate power supply, that was pressurized, and had selelium rectifiers.

One had a blown selenium stack. When we opened it up and let the air out, it not only cleared our shop, but the two shops in adjoining rooms. It took 3 or 4 hours with all of the windows and doors wide open before anybody could even go back in. (what's the smiley for "EWWWWW!!"?) ;-)

Cheers! Rich

What kind of bike, British? I'm a little confused about your use of the term magneto. To my understanding the magneto only fires the spark plugs, and an alternator or generator charges the battery.

A friend of mine has an old British bike with a permanent magnet generator, rectifiers, and a big zener diode to regulate the voltage; very primitive voltage regulation, but the bike is thirty or forty years old.

There's no need - as I remember the original post,

"I would like to build a rectifier / regulator for my motorcyle. The magneto puts out 6 Vac so it needs to rectify it to 6 Vdc and be capable of handling about 10 amps. I would like to charge the battery without overcharging it. does anyone have a suggestion or schematic"

So, it's putting out 6 VAC.

Maybe it's got another winding?

Hope This Helps! Rich

I have wondered the same; my guess that it was not done due to the

...the circuit run from a battery so it can be used "anywhere".

From what I can find out, there are 2 windings, but you probably don't have access to the low voltage one. The output is more of a pulse than AC. The following is from

"Since the magneto is a self-contained integrated ignition unit providing its own electrical power generation, a vehicle with other electrical equipment (lights, radios, etc.) also requires an alternate means to provide electrical power for that equipment, such as an external dynamo or alternator. "

Tam