Atomic ignition

A bit overdue..:-) Down here, the equivalent cost about 6 quid. My lawnmower, Victa GTS (Guaranteed To Start) had one from new, it's 17 years old, Still starts first pull..

Tom

Reading the instructions more carefully indicated that swapping the leads around might help - and it did. The spark now occurs on clockwise rotation. However it is a poor, sad thing compared with the bloody great crack that came from it anti-clockwise - very frustrating. Moving the base plate to the extremities of its travel makes no difference and spinning it over with the electric drill doesn't help either. In fact, as it works away, so the feeble spark seems to thin out even further & I doubt if it is firing the plug under compression - certainly it pops not, nether doth it burble.

I am unwillingly brought to the conclusion that the HT coil is past its use by date and needs replacing. I'll go and take its picture later on & start pleading in earnest later ;o))

Regards,

Kim Siddorn.

"Kim Siddorn" wrote

I noticed when fiddling about with the minimoto ignition set on a Wico A body that it only sparked once per rev ie, that it was polarity sensitive. But, if the coil is knacked, how come you got the 'would light water' spark in the other direction?

Not that I know too much about magneto's (apart from to try to avoid them), but if the coil is of a similar design to a "conventional" HT coil, one end of the primary would be connected to the secondary in such a manner that the voltage induced in the primary by the breakdown of the primary field would enhance the secondary spark - i.e. kick it up the ****. If the current flow through the primary is reversed the induced voltage works against the secondary voltage - kicks it in the teeth and thus reduces the HT voltage - hence poor spark.

Now, without a diagram, I have no idea if I am talking crap or not and I also have no idea how to solve the problem. I had better go back to my diesels.

Deep in my addled grey matter something is stirring!

Both coil and magneto ignition systems (except capacitive discharge) work by building up current and thus energy, in an inductor (1/2 LI^2 IIRC) while the primary circuit is closed, then rapidly transferring this stored energy to the secondary when the primary circuit is opened and the magnetic field in the inductor collapses.

The Atomic device replaces points and condenser so presumably operates in the same way - allowing the primary current to build up and then going rapidly O/C. Now the points and coil don't care which way the current is flowing when the circuit is broken (apart from the possibility of a 'backwards' spark, but many modern cars seem quite happy with that, sharing one double ended coil between two cylinders), but the Atomic is polarity sensitive.

I don't quite know where I am going with this, but could there be something in the moving magnetic circuit (shape of pole pieces etc) which means that the inductance (L) is lower when the current peaks in one direction than it is in the other? Thus, even though the current flowing when the circuit is broken was the same, there would be less stored energy to be released.

Just a thought, try flipping the coil end to end if it is physically possible.

Where can you buy one of these Atomic Kitten coils ?

I think the coil may well care "which way" the spark is going. If we leave modern high energy ignition systems out of it because the original coil was not for such a system then there is a good chance that there will be several hundred volts difference in the HT output depending upon which way round the primary current flows (I have measured it in the past).

Again, extrapolating from older vehicle coil ignition systems, a reverse connected coil primary circuit would typically give symptoms of poor starting and high speed misfires and those can both point to low HT voltage. This was very common when cars went from positive earth to negative earth because (for a very short time) both coils had their primaries marked SW (switch) and CB (contact breaker) . The manufacturers wised up and marked the coils + and -, so one coil could be used on both pos and neg earth.

On some industrial engine magnetos I have had the pleasure of playing with the coil assembly had an earth wire with an eye terminal that was fixed under a suitable bolt - often one that held the coil's pole piece in position. If yours is like this it may be worth a little experiment to see if extending this and using as the "live" connection and changing the existing "live" to the "earth" would help matters. If the "earth" is a metal strip trapped against the pole piece it would be very much more difficult.

This has nothing to do with amounts of magnetic energy stored (or however you want to put it). It is related to which way the current induced in the primary coil flows when the contacts open and cause the magnetic field to collapse. It saves complication to normally ignore what happens to the current induced in the primary coil so your explanation of operation is typically the one used and does well most of the time, however as soon as I hear anything that suggests reversing current flow in the primary coils alarm bells ring for me.

As we must be talking about sparks with the plug out of the engine the direction of spark emission at the plug is irrelevant. It only becomes relevant when one attempts to design engines to run with weak sparks and then ensuring the spark jumps from the hotter of the two plug electrodes helps. This clearly does not apply in this case.

"Tony Brooks" wrote (snip):-

Well, even If I don't quite understand the whys and wherefores, I can't argue with experimental evidence!

Is nobody going to tell me where these can be bought :-((

Mart> Where can you buy one of these Atomic Kitten coils ?

Didn't Kim mention his source in the opening post of this thread?