The BSA A7-A10 Forum

Technical => Lucas, Electrical, Ignition => Topic started by: ADP91 on 19.06. 2016 15:53

Title: Magneto question
Post by: ADP91 on 19.06. 2016 15:53
Please forgive my lack of knowledge on magnetos but is it possible to run a headlight/ taillight off a magneto?

Maybe through a voltage regulator?

If my only option for lights is a generator that's fine, just thought I'd inquire.

Title: Re: Magneto question
Post by: a10gf on 19.06. 2016 16:32
Basically a magneto produces a high voltage at low current (amps), suitable for sparkplugs, & a dynamo\generator outputs a low voltage at higher amps, suitable for lamps, battery etc.

And I dont think the magneto would like to see a voltage regulator connected instead of a sparkplug, and in my opinion, even if a 20.000 to 6 v device was available commercially, there would'nt be anything left to make a spark on the plug. But some here may have some interesting views.
Title: Re: Magneto question
Post by: RichardL on 19.06. 2016 17:50
I think "not-doable" or "don't-doable" might be an adequate answer, because coming up with an impulse to dc converter for a motorcycle is not likely in the extremis. There exists what is called a "magdyno", which combines the magneto and dynamo mechanisms in a fastened-together Frankensteinian device that will not work on our bikes.

Richard L.
Title: Re: Magneto question
Post by: Triton Thrasher on 19.06. 2016 18:20
The ML Maglita used the unused wave on a single cylinder magneto to power the lights.

They say it wasn't very good. (
Title: Re: Magneto question
Post by: groily on 20.06. 2016 10:53
Ha! Not really very good at all TT. What with a max of about 3.5A on the bigger ones. But they don't work like a typical mag, as there's a lighting armature with a simple 2 part commutator, as well as a primary and secondary winding relying on the lighting armature as an inductor for the sparks, and a series of tweaks (centrifugal self-locking lighting armature cut-out, a compensating winding comprising half the low tension ignition circuit, etc) designed to get round the inherent weaknesses of the design.
To be avoided unless originality is absolutely essential I'd say.
The original M-L leaflet (600.1 from Sept 1930 is the one I have) is full of laughable statements implying you get the best of both worlds, simplest thing ever made etc. But when economy was the watchword, and when they were new  . . . maybe they were OK. The simple bar magnets sure as heck need to be as saturated as they can be got! They claimed to be OK on 500s, outfits etc etc - but quite honestly, a bit of a development blind alley I'd say, although there are a good few still, out there (a lot of them on small Beesas of those days it has to be said).
Re the original question, you won't get lights out of a typical mag, No. I had a chap who swore blind that his grandfather had used a twin cyl mag on a WW1 vintage single, with the second pick-up being used to produce some sort of glimmer of light - but I'm darned if I can see quite how and wouldn't want to try. I just don't see how you'd get enough current out of the thing without putting it in harm's way. But maybe there are clever tricks out there, and with LEDs etc, who knows?
Title: Re: Magneto question
Post by: coater87 on 21.06. 2016 20:36
 Odd little question. *conf*

 Groily, what is the turns ratio on a magneto like the K2F?

 I ask because the only way I could see this maybe working, even a little bit is with a second mag armature used as a step down transformer. But even then I am not positive because the inductor would resist a change in current, but the secondary side (now opposite of a normal K2F) may be able to carry through enough that the (small draw) bulb would not flash noticeably enough to look like a strobe light. Maybe. And I wonder if it would last at all, or just quickly heat up and turn to a pile of smoking rubble... *conf*

 This goes back to the days of being an apprentice, and is WAY outside of what I really do, and my real job is a lot less fun than the bikes. *sad2*


Title: Re: Magneto question
Post by: groily on 21.06. 2016 22:03
100:1 is the oft-quoted yardstick for HT mags generally Lee, but winders have their individual preferences I believe.
I haven't really thought much about trying to get illuminations (of the non-spark variety) out of the things, as I'm sure it's a non-runner in practice, even if in theory a tiny bit of something might be manageable. Takes a bit of current (more than a mag's ever realistically going to provide) to get a filament to glow, especially from cold. After all, some dynamos will struggle to light high wattage 6v bulbs wired directly off them, and they're designed to whack out at least a handful of amps!
I do smell smoke here, and think claims that may have been made from time to time are a bit on the snake-oil side! I suggested to the gent who thought his grandad had done something like this that the way forward on a veteran would be a bolt-on acetylene kit. (Or a bicycle lamp!)