Can you stack 2 ignition coils together?

[nsled]

I want to join 2 ignition coils together to double the voltage. Can this be done by "phasing" them like a neon transformer works? ie. One side is negative while the other is positive. I've attached a crappy picture but I'm not sure if that's correct or how to wire it, I've labelled all the terminals so it's easier to describe.

[Nusa]

That diagram puts them in parallel. I would expect zero increase in voltage, but you will get an increase in current capacity. Which means they're more capable of killing you by mistake in that configuration.

Out of curiosity, what's your application that requires more than the already high voltage an ignition coin puts out?

[Psi]

You can wire them so one produces +HV and one produces -HV and then you have double the potential between them.
You can also run them on 20V instead of 13V and get bigger arcs, but lifespan will be a bit reduced.

[magic]

Some/many/most/all(?) old coils of the sort that the OP drew aren't even meant to work on 12V.

In cars they are used with external series resistance which limits their voltage to little more than half battery voltage, and IIRC this was deliberate.
(The ones I measured had maybe an ohm or two of their own resistance on the primary.)

[nsled]

That diagram puts them in parallel. I would expect zero increase in voltage, but you will get an increase in current capacity. Which means they're more capable of killing you by mistake in that configuration.

Out of curiosity, what's your application that requires more than the already high voltage an ignition coin puts out?

Parallel but with the current flowing through the primary winding in opposite directions. Since ignition coils output AC, the point is to get the secondary HV terminal at negative potential while the other is at positive thus having 2x voltage without straining the coils.

[p.larner]

would a diode+cap multiplier not be better,as in cockcroft walton i think its called?.

[magic]

It doesn't output AC, not in the usual sense.

Like every flyback, it produces a pulse of secondary current every time the primary current is interrupted. The induced secondary current is turns ratio lower than the primary current which had been interrupted, so for instance a typical 1:100 automotive coil produces 10mA per 1A of input. The secondary current charges capacitance of the winding and external cables until enough voltage develops to strike an arc. During this time, a 100 times lower voltage (so maybe 200~300V) appears on the primary and must be blocked by the interrupting circuit (mechanical switch or transistor).

The primary switching circuit should actually break down and start conducting near this voltage, in order to prevent excessive voltage from appearing on the secondary and damaging coil insulation. BTW, I'm not 100% sure if the limits I give are entirely correct or if lower voltage limit would be safer for the coil or maybe higher could be gotten away with.

The amount of energy delivered into the spark is determined by primary current before interruption, primary winding inductance and "efficiency", which depends on primary leakage inductance and resistive and capacitive losses on the secondary. Total energy in the primary is the usual I²·L/2 and I suppose a large fraction of it is delivered to the spark.


I think your idea of connecting two coils in opposite polarity should work. You will need to ensure that both primaries are interrupted at the same time; this means that transistor drive is the best option.

[G-son]

Interesting idea. What would be the use for your double coil creation (assuming it works)?