The correct coil current seems to be 1.3 Amps on the HCCT or other measuring devices.
That is reported to be an average value and different from the way the coils function in the vehicle, as the current only flows through one coil at a time and for less than 90 degrees of the total timer loop.
How much less is not exactly known, so I took and original timer and measured the contact area that would let each coil fire. They all appear about the same, but the average value in this timer would produce sparks from a coil for 43 degrees of the 360 degree loop.
Getting back to the average value, the real question is what would the value of this current flow be, if I could devise a way to measure the actual current flow for each coil.
If I multiply 43 X 4, I get 172 degrees that current actually flows during each timer revolution. That would seem to suggest a current of a little more than 2.6 amps on to produce the 1.3 amps average value. All the coils get their power from the same strip at the bottom.
One of our club members has one coil that gets hot and melts out the tar. It is not easily to understand why a replacement coil does the same thing. If the coil was drawing current for more than the normal amount of time, it would appear that the engine would have to backfire when the cylinder is firing at the wrong time.
Does anyone understand this problem better than I do?
Current does not flow to the coil for the entire time the timer is in contact with the roller. Your thinking is logical but flawed.
Go to the Fun Projects website. You need to read up on what is actually happening.
James, I don't really understand the purpose of your post. Apparently someone has a problem with a coil overheating?
There seems to me to be a few mistakes in your thought process. I will try to help you with that.
You said: "The correct coil current seems to be 1.3 Amps on the HCCT or other measuring devices."
This is more or less true.
Then: "That is reported to be an average value and different from the way the coils function in the vehicle, as the current only flows through one coil at a time and for less than 90 degrees of the total timer loop."
This is where the thought train leaves the track. The coil when operating on mag in the car should have an average draw of 1.3 amps the entire time that the timer is in contact. The current value is a function of the point setting of the coil when operating on mag in the car, much as it is on a HCCT, and not a function of how many degrees of timer contact there is.
The coil fires at 1.3 amps. That is the current builds up to 1.3 amps by charging the capacitor until it reaches 1.3 amps. Then the capacitor discharges quickly causing a high voltage to flow in the secondary coil. This will happen only once every other revolution for a particular coil. If you are running on battery, the capacitor will discharge every time the current reaches 1.3 amps which could be more often than once. per 2 revolutions.
The reason for setting all coils on a coil tester to fire at 1.3 amps is that if you set it higher, that coil will spark late and if less that coil will spark earlier. The timing will be off for the cylinders which fire later or earlier. So the current should be set as close to 1.3 amps as possible.
If your friends coil is overheating, and the replacement is overheating the problem is obviously a continuous ground on the timer wire for that coil causing it to buzz - continually. I'd check the complete harness.
Norman, the average current draw is 1.3 amps. The coil current (usually) actually ramps up higher than that each time it fires. The current does not build to 1.3 amps by charging the capacitor. Capacitors store potential (voltage) not current. The capacitor is actually initially out of the circuit as it is shunted (shorted out) by the points. The capacitor charges when the points begin to open. A coil can fire several times per revolution when operating either on battery or mag.
On 6V DC, the peak current is about 4A which is reached in 3.5mS, at which point the coil fires.
Increasing the coil current delays firing, but also wastes power because the coil starts to saturate beyond this point. Reducing coil current decreases firing time but of course reduces power. Setting my coils electronically like this means they all have the same firing time.
It's no coincidence the point at which the coil is set to draw most current without saturating is about 1.3A average current.
I'm beginning to understand this problem a little better now.