Ignition Coil Specification Differences

[Harte3]

Coil #1 51,000 v Spark Duration 250 uS
Coil #2 45,000 v Spark Duration 350 uS

Coil #1 Primary Resistance 0.500 ohms Secondary Res. 8.9k ohms
Coil #2 Primary Resistance 0.700 ohms Secondary Res. 4.70 ohms

Being electronically challenged, what do these differences mean in terms of: 1. Power required to operate them and heat generation? 2. Power delivered to the spark plug? 3. And differences if any in the quality of spark at the plug?

 

[Lazy JW]

I was hoping someone better qualified would jump in here; I am only a technician, NOT an engineer but I'll take a stab at it.

One thing missing from your data is if the coils require the use of an external resistor or not. Also, some coils have additional resistance built inside them. I will assume there is no additional resistance designed into either coil; this may be an error on my part.

Primary resistance is what mostly controls the amount of current flowing into the coil when it is "charging" up. If the coil has sufficient time this current will eventually "saturate" the coil and it will not build up any more energy. At this saturation point the coil needs to fire or it will just generate heat (a bad thing).

Principle #1; Lower primary resistance = more current which produces a stronger electro-magnetic field which "can" make stronger sparks.

Principle #2; Higher secondary resistance is usually from having more winding turns (possibly of smaller wire). The more secondary winding turns the higher the output voltage can be but THE LOWER THE CURRENT will be.

Principle #3; The higher the voltage the shorter will be the spark duration in addition to lower current.

Principle #4; When the primary current has saturated the coil and the current flow is then interrupted (breaker points open) the electro-magnetic field collapses: this induces a current in the secondary windings which will build up an electro-magnetic field causing the voltage to rise proportionally to the ratio of winding turns. THIS VOLTAGE ONLY INCREASES UNTIL IT CAN JUMP THE SPARK PLUG GAP! Once the gap is jumped, voltage drops to around 1500 volts or so as it "pushes" the current through the gap. The amount of this current (measured in Joules) and the duration of the spark are crucial to "building the fire". More current and longer duration are good things at this point in time.

I'm not quite sure how to rate your two coils, but I would guess that Coil #1 would require more power to operate but could fire a wider gapped plug and "may" be able to fire through more fouling and be better able to fire a plug in a supercharged application due to its higher voltage potential.

Coil #2 would require less power to operate and would do a better job of firing a lean mixture at part throttle in a mild street engine due to its longer spark duration and possible higher output current.

I could be all wrong on my assessment of the coils however.
Joe

 

[Harte3]

Thank you kindly!

I have noticed quite a difference in coil specs (browsing catalogs too much) and wondered what they mean. Some very high v coils (61k) have seemingly low spark duration compared to lower v coils. Coil winding ratios vary from 50:1 to over 100:1, etc., etc.

 

[Lazy JW]

.... Some very high v coils (61k) have seemingly low spark duration compared to lower v coils.....

Yup. It can be a mistake to buy a coil based solely on voltage rating. Having a long spark duration is an advantage on a lower-powered engine as it gives a better chance to encounter more fuel molecules, especially at less-than WOT. At WOT there is a more dense charge of air/fuel mixture so the molecules are packed together more tightly, giving increased contact with the spark kernel. The problem at WOT is you need to be able to jump the spark gap so higher voltage is necessary.

One advantage of higher voltage capability is the fact that you can run a wider gap; this automatically increases the amount of molecules contacting the spark kernel from the simple fact that the distance is longer. Trouble is, this also shortens the duration.
Joe

 

[Geezer 300]

I think I used to be a coil when I was younger

 

[Harte3]

http://www.hotrod.com/techarticles/igni ... index.html

http://www.breakerless.com/igntionfacts.htm

Two sites I stumbled on that in many words said what Joe said in few words

And Geezer, I know what you mean...less gap and duration now