White wire succses story!!!!

[MurraySabrePlus]

I don't think these dinky cells will be of much use,but that of course depends on your energy needs.I agree about the power rating of the diodes.But the frequencies are so low (less than 100 hz) that to require fast-recovery diodes are to be used, makes simply no sense.These are used in high freq switching supplies at 100 kHz or so. Schottky diodes which are inherently fast recovery types,could produce somewhat higher output because of their lower voltage drop, but are more expensive.

Not to argue with you JJ, but being an electronics tech and servicing television sets (including horizontal frequency & switch mode pwr supplies) for years, I happen to know that replacing a standard 60hz diode in a circuit that switches at high frequencies will eventaully stress and fail.

At the speeds of these 2 stroke engines being in the 1000's of rpms, I'd prefer to play it safe then el-cheapo, and use a proper diode.

 

[etacovda]

Just HOW do you come up with 133 hz from say, 8000 rpm?
Since the sparkplug fires with each revolution/compression stroke and that correlates with the pulses from the magneto, one would think 8000 rpm would equal 8000hz.
Enlighten me.

er, simple math...? 8000/60 = 133?

 

[MurraySabrePlus]

er, simple math...? 8000/60 = 133?

Certainly that would be correct, but...
Enlighten me as to this mysterious "60" figure, and where does it come from?

 

[etacovda]

that would be the amount of seconds in a minute.

 

[duivendyk]

Rpm means revolutions per MINUTE not SECOND,what happens during an ac pulse is faster them the rep. rate,possibly 10 times as fast, so as far as speed is concerned we might be dealing with around 1 khz, not all that fast.I'm not against playing it safe,I'm all for it, even if it is of doubtful benefit,provided that it doesn't cost a small fortune.

 

[MurraySabrePlus]

It seems to me, if we're talking about 2-stroke engines here, and the VARYING revolutions of such engines is from 1000-8000 rpms......AND the spark pulse is for EACH revolution, then those pulses in the magneto to trigger EACH spark is the SAME speed.

THUS..... we're dealing with HIGH-speed A.C. pulses, well over what a 60hz diode can efficiently handle without eventual failure.
Yes, at 8000 RPM, the AC component is around 133hz, but with sharp spikes, unlike a clean house current waveform (sinewave).

And THUS, the necessary use of a diode designed to deal with these sharp, high-frequency spikes..... to insure reliablility, efficiency and safety.

Come on guys, I know some of you are not experienced in electronics design, you're just backyard mechanics puttering around with the idea of powering a battery from the engine magneto to use some lighting with.

All well and fine, but since I'm more knowledgable about these things, I'm trying to educate you on the differences of semiconductor designs, and why you just can't use any old rectifier diode for this application.

If that diode fails, it'll short out, and the result will be full battery voltage across a 2 ohm winding in the magneto. I'd also suggest a fuse (1-2A?) in line with this diode for additional safety.

Diode shorting will effectively and instantly shut down the engine by magnetizing the whole magneto, disrupting the rotating magnet's pulses to fire the sparkplug, and in a few seconds burn up the windings, rendering the magneto toast. A couple of amps of DC from the battery across a small 2 ohm coil will make it fry real fast.
If you're tooling along at 20-30+ MPH when this happens, I hope you have your helmet on, and your health insurance paid up.

If you don't believe me, run the engine at idle, and briefly touch a 6 or 12 volt battery to the black/white wires, and watch it fumble, maybe stop alltogether, if left on there long enough.

Or try it on a junker engine.

 

[duivendyk]

You really amaze me MSP, you persist in error and appear to be incorrigible.Get it through your thick skull once and for all that these engines are running at 6 thousand revolutions per MINUTE or a mere 100 per SECOND, get it, 100 per SECOND or 100 Hz.As for blundering ignorant shadetree mechanics we know a thing or two about elementary math like n revs/min equals n/60 cycles/sec BTW, I happen to have degrees in both mechanical and electrical engineering and decades of experience in both fields.
Since the engine is stopped by a short on the WW the possibility of zapping the entire coil is simply nonexistent,also there is little current in that part of the winding anyway (330 Ohms) and zero when it stops.You also seem to think that the engine comes to a dead stop instantaneously,It will wind down and I would instinctively pull the clutch and get off the road,I would be most likely in the right lane anyway.

 

[MurraySabrePlus]

You really amaze me MSP, you persist in error and appear to be incorrigible.Get it through your thick skull once and for all that these engines are running at 6 thousand revolutions per MINUTE or a mere 100 per SECOND, get it, 100 per SECOND or 100 Hz.As for blundering ignorant shadetree mechanics we know a thing or two about elementary math like n revs/min equals n/60 cycles/sec BTW, I happen to have degrees in both mechanical and electrical engineering and decades of experience in both fields.
Since the engine is stopped by a short on the WW the possibility of zapping the entire coil is simply nonexistent,also there is little current in that part of the winding anyway (330 Ohms) and zero when it stops.You also seem to think that the engine comes to a dead stop instantaneously,It will wind down and I would instinctively pull the clutch and get off the road,I would be most likely in the right lane anyway.

And you mister JJ, certainly don't amaze me... why?

Typical internet blabber is one reason.
Typical retort from a "college degree lad" is another. (I've heard it all before)

You must think people with degrees know more than people with EXPERIENCE.
Your statement about "Since the engine is stopped by a short on the WW the possibility of zapping the entire coil is simply nonexistent,also there is little current in that part of the winding anyway (330 Ohms) and zero when it stops." COMPLETELY misses what I said in my post.

But then, you don't have the experience that I do... You only have those "degrees".

Do things your way dude... ok? and good luck.

 

[duivendyk]

Some people profit and learn from experience,you seem to be the exception.The fact is that you can't bring yourself to admit that you were completely wrong about the number or revolutions PER SECOND that an HT engine makes.It can do about 6000 rpm max or about 100 per second,not 6000 Hz or more as you claim, which is not all that much above 60 Hz. Get that through your head.Only a few diodes I have ever come across failed by shorting out,most just vaporized the junction& exploded,of course you know better.As far as blowing up the rest of the coil in the few seconds until the engine is supposed to stop.That is rank nonsense,complete drivel.If anyone is concerned about the diode shorting out for whatever reason, there a simple fix,a fuse will take care of that.If I was supposed to have completely 'missed' what you had to say,please enlighten me on that score,it would be interesting to find out what that might have been,your inacquaintance with or disdain of elementary arithmetric?

 

[MurraySabrePlus]

You obviously never worked "hands on" in an electronic repair shop, or you'd eat your own words, but I assume stubborn virginny people are just that.
I'd never hire you to work in MY shop for that fact.

I'm not rigid about discussing the actual cycles per second NOR the revolutions here, because you're somehow not familier with high-speed spikes that are a part of rudimentary generation from these magnetos and even in television flyback circuits.

You'd be replacing flyback-derived power/deflection diodes with standard 1N4007's and costing me money on callbacks!.... no thanks!
Enough of this. push on now... please.