Herbert A magneto works much the same way as a coil - except it is self excited. There is a low tension side which is "normally" short circuited by some sort of switch, and a high tension overwind similar to the secondary winding of the coil or transformer. The magnet moving past the windings induces a current in the primary which, at the appropriate moment, is interrupted by the switch opening. The current in the primary suddenly has "nowhere to go" and the voltage across the primary rises dramatically. Since the secondary winding is on the same magnetic circuit, it's voltage rises even more dramatically as it has more turns and is sufficient to break down the spark gap & fire the mixture. To my knowledge there are no systems that generate the secondary voltage directly from the magnet/coil arrangement - and spark timing would be a major problem with this system anyway. As I noted earlier, 2 stroke engines can have points (generally well buried under the flywheel) or more commonly these days, a transistorised module that detects the current in the primary winding and opens the transistor switch as soon as this current starts to decay (i.e. as the magnet moves away from the gap in the coil) - or something like that (I haven't looked in detail but have had to replace a module or 2). Hope this helps. I realise you may not want to get too involved with rewiring the magneto so suggested the spark plug shorting method. Another advantage that comes to mind is that it may be possible to arrange it as a kill switch if the car flips etc. although vibration could be a problem. Richard P Herbert Graf cc: Sent by: pic Subject: Re: [PIC]: Building a Servo microcontroller discussion list 10/08/01 11:36 Please respond to pic microcontroller discussion list But AFAIK there IS no "low tension side of the magneto". The spark is created when the magnet on the crankshaft passes by the stionary coil, which results in the spark. Please correct me if I'm wrong, remember, this is a small 2 stroke engine. Thanks, TTYL > -----Original Message----- > From: pic microcontroller discussion list > [mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Richard Prosser > Sent: Thursday, August 09, 2001 16:24 > To: PICLIST@MITVMA.MIT.EDU > Subject: Re: [PIC]: Building a Servo > > > I think the suggestion was to put a relay across the points/sensor on the > low tension side of the magneto. > > Richard P > > > > Herbert Graf > RCITE.NET> cc: > Sent by: pic Subject: Re: > [PIC]: Building a Servo > microcontroller > discussion list > .MIT.EDU> > > > 10/08/01 08:16 > Please respond > to pic > microcontroller > discussion list > > > > > > > > -----Original Message----- > > From: pic microcontroller discussion list > > [mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Douglas Butler > > Sent: Thursday, August 09, 2001 15:50 > > To: PICLIST@MITVMA.MIT.EDU > > Subject: Re: [PIC]: Building a Servo > > > > > > > I might also add a redundant kill switch with a > > > second transmitter and > > > receiver, the only problem, and this is something I was > > > planning to ask, is > > > how do you stop a gas engine remotely? I thought about > > > disconnecting the > > > spark plug but how would I do that considering the voltages involved? > > > Cutting the fuel flow is a second idea but my experience with > > > two stroke > > > engines is that they keep running, without any fuel flow for > > > at least 30 > > > seconds, long enough to cause damage. Anybody have a better > > > idea? Thanks, > > > > How about some relay contacts across the breaker points for the ignition > > coil, assuming you have mechanical points vs. electronic ignition? The > > voltages there are reasonable and without spark the engine should stop > > quickly. > > I was thinking about something like that but it may be > hard to find > a relay > that can do it. The problem is that if the relay contacts aren't > far enough > apart a spark will simply develop across the relay contacts AND the plug! > :( The motor I am using (and no I can't change the kind of motor being > used! > :) )uses a "coil flying by a magnet really quickly" approach to > develop the > spark. > > Why I don't really like this idea either is that assuming I find a relay > with contacts far enough apart it is still possible that on say a > humid day > the spark WOULD jump across the contacts. I guess I could heavily modify a > relay so the contacts are say 1cm apart, I believe that would be enough, > but > being a safety device I'd rather go with something a little more > "sure". :) > TTYL > > -- > http://www.piclist.com hint: To leave the PICList > mailto:piclist-unsubscribe-request@mitvma.mit.edu > > -- > http://www.piclist.com hint: To leave the PICList > mailto:piclist-unsubscribe-request@mitvma.mit.edu > > > > -- http://www.piclist.com hint: To leave the PICList mailto:piclist-unsubscribe-request@mitvma.mit.edu -- http://www.piclist.com hint: To leave the PICList mailto:piclist-unsubscribe-request@mitvma.mit.edu