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Newfangled ignition coils

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geoff_p:
For my hit 'n miss engine I need an ignition coil.  I had hoped to use the old familiar points + condenser + coil method, and there are plenty of circuits shown on the web about them but tracking down a suitable coil is not so easy over here in Thailand.

However, motorcycle coils are plentiful, at least the newfangled ones are.  They seem to contain some electronics but with no indication of even the polarity, let alone the workings.  (I know this because I just took one apart by melting-out the pitch that filled the case.)  The only markings/label on the one I just bought are "MAX R" and a Google search for that just didn't help at all!

Can any of you explain
a/ How they work;
b/ How I might use a newfangled coil?  I'll go away from points if I have to.

Cheers,

Geoff

krv3000:
hi i will find a pic that i have and sum info on the  one im thinking of its the type that you will find on lawn mower engins they get trigerd by a magnet on the fly wheel i will post you the info tonight but whot i think you id describing is the ampleyfier IE ther is no ponts ther is just a magnetic triger on the fly wheel ther is a magnet this pases over the triger this sendes a small eletrikel pulse to the ampleyfier wich then trigers the coil to spark sos for the spelling

krv3000:
hi will this help

geoff_p:
Thanks for that, KRV.  Unfortunately, it doesn't help - the lower part of that pic is just about what I have been trying but with a new coil in its place.  The primary current is something over 10 Amps (the books all say 1.5 to 2 Amps), and the coil becomes untouchably hot in a few seconds.

The type of magneto-coil depicted had no electronics in it, it was a simple transformer in effect.

The coil I have never went even close to the engine - it's mounted on the chassis, somewhere under the saddle - so it never gets a magnetic pulse, either as power or as a trigger.

The guts of the coil I broke-up clearly contains a circuit board with some resistors, a large capacitor and a power-transistor, all of which suggest the thing should be polarity-sensitive.  But which polarity?  My Honda motorbike's manual gives no indication.

I'm guessing that both power AND control-pulse must come in to the thinner wire - the fat one is HT to the plug - and there was a second, orange lead riveted to the core, which I assumed to be ground/chassis return to the battery.

Geoff

awemawson:
Well lets do some (dangerous!) assuming. Assuming that the coil mounts to the chassis of the motorbike then the extension of the transformer core, which seems to be being used as the mounting, must be the polarity of the bikes chassis. Since about 1970 practically all vehicles have chassis negative, so I reckon that there's a 95% chance that the transformer core is negative, hence the other conection must be positive. It probably has a simple 'amplifier' ie current switch in this case so if you have powered it up probably the switch was permanently 'on' hence the high current draw - it will be expecting pulses from the sensor in the engine.

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