Forum

[Count Johnny]

Gentlemen

A question for clever people (which counts me out!).

Am I correct in thinking that the coil draws more current before the engine is started (ignition on) than after the engine is started and, if so, why?

Am I also correct in thinking that the current drawn continues to reduce as revs rise and, if so, why?

Finally (being really cheeky) does anyone have any numbers for static, 1000rpm, 1500rpm, 2000rpm, 3000rpm (1996 500 Bullet)?

Thanks in advance (if you'll pardon the near pun).

[simon]

The coil only provides a resistance when the points are shut. So with the motor stationary and the points in a closed position the draw is constant whereas when running the coil is being switched on and off. The resistance though I believe remains the same.

[Frank]

The primary coil will permanently drawing current when the ignition is on regardless of points position on the secondary. Maximum current will be drawn with the points closed. With the engine running the points will be continuously opening and closing so the current drain will be fluctuating but I wouldn't have thought by much. As the engine is running the coil will warm up and the resistance of the coils will reduce and so slightly more current will be drawn. My theory anyway and probably completely wrong!

[Dennis C]

"My theory anyway and probably completely wrong!"

You are correct Frank, -------------- completely wrong.

[Scalyback]

Induction

Reactance

Reluctance



point open, no flow through coil.
points closed flow through coil.



How 6 or 12 volts turns into thousands...



the points complete the circuit. when they open, they breal the circuit and the spark plug fires.



We don't need to know the theory, but power runs through the coil building up a magnetic field, when the points open, the Magnetic field collapses, and through induction, produced very hign pressure (voltage) in a secondary coil in the induction coil, which becomes thousands of volts, enough to jump the gap in the spark plug.



In terms we understand

I am certain you have all been somewhere with a bit of dodgy plumbing? well when the point close, it is like opening the tap (faucet) suddenly. the water starts to come out quite fast. When the points open, it cuts of the electricity to the coil, just like slamming the tap (faucet) closed very fast. Sometimes you can make the water pipes 'bang'. that is the sudden back pressure when the fast flowing water suddenly finds the tap closed and the pressure comes from it all having to stop suddenly.



It is NOT quite the same with a coil, but it helps to think of it like that. the electricity is flowing through with the points closed, they open, "bang" the back pressure is so great that it jumps the spark plug gap.



YAY! Scaly-speak

[PeteF]

Come on then Dennis!

[Frank]

Dennis, hmmm am I that wrong? Surely the primary coil is a resistance connected directly across the battery and thus must drain a current through it. With the points closed across the secondary coil the load must increase until the points open, the field collapses and the HT voltage is released. Maximum current must therefore be drawn with the points closed and minimum when open and so must fluctuate when the engine is running between Max and Min but always some. To the original question as to whether the coil draws more current when the engine is stopped I would say yes, provided when stopped the points were closed, as when running the current would be varying between Max and min depending on the points position.

[Frank]

Dennis, having slept on it I can see, my foolishness. The points control the primary. Current will be all or nothing.

[JTL]

Hi all... having had problems with an aftermarket coil (and because of this been looking into what kind of coil then to substitute the Lucas coil with) I've learnt coils are not just coils. We have a primary and a secondary circuit and their different resistance values to deal with. We have the different number of windings in the two circuits to deal with. We have two different kinds of coils: oil filled and epoxy filled. We have vertical and horizontal mounting on the bike to deal with. Maybe even a few more factors in question when looking for the optimal coil for a Bullet... I have heard that the primary coil resistance should be around 3,5 ohm to suit the Bullet best. The secondary resistance should be at least 2000 times bigger to produce a strong enough spark. And that the secondary coil should have more than 150 windings for every winding in the primary coil... Please, can some of you guys enlighten the less enlightened of us on the subjects... all the best Jacob

[Dennis C]

OK Guys
I have been away a copuple of days, sorry for the delay coming back, Frank you are correct second time around having had a sleep.
The coil is not connected and draws no current until the points close, therefore points open no current draw, points closed maximum current draw, when the engine is running regardless of revs the current draw in theory remains constant, I say in theory because there are other factors to consider, lets assume for the moment that the points are closed for 25% of the cam/points rotation and open for 75% of the rotation therefore the current is being drawn for 25% of the time regardless of how fast the cam/points rotate, there are as always slight variables to consider if you wish to be pedantic, the main one is the possibility of points bounce at higer revs, but to be honest the speed that a Bullet engine rotates and the point/cam at half engine speed this does not really need to be considered.