More Ignition Experiments

nutgone wrote:The best way to think of it is like this:-
The coil you are winding is a power source. This power source is replacing the 6v (or 12v) battery in a normal car or motorbike coil ignition system. Therefore, one side of your newly wound coil (thinking of it as a battery) needs to go to earth (the same earth as the points eventually ground out to, so the magneto back-plate). The other end of your newly wound coil needs to go to the auto-type ignition coil, where the power source would have previously gone (so the positive side, or whatever it says on the coil).

From there on it's a normal car-type ignition system, where the negative side of the auto coil (the only remaining, as yet unconnected low tension terminal) goes to the insulated side of the points (along with the condenser, so could even be connected to the condenser wire).

So keep your newly wound coil ends reasonably long, so you can switch them over & try it both ways. Basically I've no way of knowing which end will be better as the polarity of your new coil depends on the direction of the windings in respect to the direction of the magnetic field passing over it. So to reverse the polarity of any simple coil you simply change the end connections over. In theory one way will work better than the other, but in reality the difference will be so slight I doubt you'll notice a difference.

Unfortunately Paul's diagram above (thanks Paul) just needs the points moving so they are between Lt2 & "handy earth point", which is already built in. Then substitute the points (as they are in the diagram) for a straight through, uninterrupted wire.

A stop switch on that diagram would go from Lt2 to earth (effectively holding the points closed). It would need to be open for running & closed for stop.

I can't do diagrams like Paul, well I probably could, but I would need to teach myself & that could take time, but I could draw it out on paper & take a photo if necessary.

nutgone wrote:For the flexible coil end connection wires just use any bits of flexible cable you happen to have lying around. I just used the 3 different coloured pieces from a normal piece of household flex. I think I used green/yellow for the points, brown for one end of my coil & blue for the other, then led them through a suitable hole in the back plate of the magneto, so I could change wiring without having to keep taking the flywheel off.
Just remember which colours went where.

Also, tape over the soldered joints (from flex to solid coil wire) & tape the whole thing over the coil, so the only movable wires are flexible ones.

Remember to make sure your finished coil isn't too big, or it'll rub on the inside of the flywheel.

Funny, since this thread has been revived I've been dismantling my latest project, a 1937 German army, Auto Union, 2 stroke portable battery charging generator (my god those Germans were so far ahead of us on 2-stroke design back then!). Anyway, that's got a flywheel mag & the coil is reading open circuit. It will probably end up being my first flywheel mag re-wind (I've been told by a professional magneto rebuilder to stay away from flywheel mags, apparently they're a pain in the arse) but until then it may well have this system applied to it.

chiefy wrote:By the way Matt did you know that the bsa bantam is a copy of a German engine I think it was D K W engine the Allies nicked the design after the war was over, there were others maybe Excelsior was another my memory is not what it used to be.Best Wishes Keith.

nutgone wrote:

chiefy wrote:By the way Matt did you know that the bsa bantam is a copy of a German engine I think it was D K W engine the Allies nicked the design after the war was over, there were others maybe Excelsior was another my memory is not what it used to be.Best Wishes Keith.

I did know that. Interesting how we managed to keep a pre-war design running right into the 70s. The engine I'm working on at the moment is Auto Union (same badge as modern Audi) but most people refer to it as a DKW, as they were part of Auto Union at the time. I think most of the Auto Union companies ended up on the other side of the iron curtain after the war, but it's also interesting to note that their later 3 cylinder car engine (a loosely based version of which ended up in the old Saabs that did so well on the rallying circuit) actually came from a pre war Scott motorcycle engine. Only a handful were made & one was in Paris when the Germans invaded. They commandeered it & sent it to their 2-stroke division for evaluation. A few things were changed (like the oiling system) but much of it remained the same. They never put it in a motorbike though, only in cars. Scott actually made a prototype 6 cylinder version which went under the bonnet of an Aston Martin! Imagine that, a 2-stroke Aston!