# How would you select an 'ignition coil' ?

#### Externet

##### Active Member
Looking for a simple choice of a coil with a largest number of turns, an automotive ignition coil comes to mind.

Am after the largest number of (secondary) turns and a straight bar type core, not 'E' core. How to select/pick such ? Measure secondary inductance ?
Can you suggest any other off-the-shelf items that could be a source of 'zillion' turns coil ? No significant current needed.

#### debe

##### Active Member
theres heaps of these types of ign coils on Ebay. This one is off a Kipor inverter generator & powered by a separate ignition module. My tester wouldn't read the secondary as inductance only resistance.

#### chemelec

##### Well-Known Member
Looking for a simple choice of a coil with a largest number of turns, an automotive ignition coil comes to mind.

Am after the largest number of (secondary) turns and a straight bar type core, not 'E' core. How to select/pick such ? Measure secondary inductance ?
Can you suggest any other off-the-shelf items that could be a source of 'zillion' turns coil ? No significant current needed.

Why do you want the higher number of turns?
My Understanding is All the older Car Coils have a 1:100 Turns Ratio.

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#### jpanhalt

##### Well-Known Member
Letting us know what are you using it for might help.

I have a buzz/vibrator coil that I use to start a small pulse jet. They give a pretty good spark, but some of the prices on eBay seem outrageous. Mine appears newer than early 20th century, maybe NOS, or maybe new replica. It was purchased this century and cost about $12. Here's what they look like: John #### shortbus= ##### Well-Known Member Letting us know what are you using it for might help. I have a buzz/vibrator coil that I use to start a small pulse jet. They give a pretty good spark, but some of the prices on eBay seem outrageous. Mine appears newer than early 20th century, maybe NOS, or maybe new replica. It was purchased this century and cost about$12.

Here's what they look like:
View attachment 110004

John
Model T Ford coil. Or that's what they used. They had four of them each feeding the 'distributor'.

#### Externet

##### Active Member
Letting us know what are you using it for might help...
Am building a differential gradiometer; do not have winding equipment and exploring what is applicable/available off-the-shelf.

#### Ian Rogers

##### User Extraordinaire
Forum Supporter
You want a coil from an old car with at least 6 cylinders.. That way the coil will have the greatest output as it has the least time to fire..

Older cars used to need 14kv across the spark gap.. Nowadays its more like 8kv.. Latest cars have a coil per cylinder..

#### jpanhalt

##### Well-Known Member
If you look for racing coils, you will find some spec'd to 80 kV or more. Don't know whether those specifications are bloated, but higher compression needs higher voltages, and higher voltage at 12V must mean more windings. They can get kind of pricey.

#### MikeMl

##### Well-Known Member
If you look for racing coils, you will find some spec'd to 80 kV or more. Don't know whether those specifications are bloated, but higher compression needs higher voltages, and higher voltage at 12V must mean more windings. They can get kind of pricey.
Actually, the secondaries have about the same number of turns; what they did is reduce the primary turns so the step-up-ratio is higher...

#### jpanhalt

##### Well-Known Member
I never paid attention to either. My pulse jet is "low compression."

#### chemelec

##### Well-Known Member
Reducing the Primary Turns to Increase the Turns Ratio Does Not Increase the Output Voltage.
The turns ratio on older coils is 1:100.
So based on 12 volts in, the output would be just 1200 volts.
Car Coils work on a Fly-back Principal to increase Voltage.

#### ClydeCrashKop

##### Well-Known Member
Something that wasn't mentioned yet is that some coils have an internal ballast resistor.
You don't want one of those.

#### tomizett

##### Active Member
Reducing the Primary Turns to Increase the Turns Ratio Does Not Increase the Output Voltage.
The turns ratio on older coils is 1:100.
So based on 12 volts in, the output would be just 1200 volts.
Car Coils work on a Fly-back Principal to increase Voltage.
Granted, but surely a lower number of primary turns means less primary inductance and a faster rate-of-rise of current while the points are closed. So if the points are closed for the same time then they will open at a higher current - meaning more stored energy and a higher voltage spark.

#### schmitt trigger

##### Well-Known Member
I never paid attention to either. My pulse jet is "low compression."
Pulse Jet?
You mean like a V1?

WOW! That would be very interesting to watch. There are several pulse jet videos on Youtube used on model airplanes. I wonder if yours is there.

#### jpanhalt

##### Well-Known Member
Pulse Jet?
You mean like a V1?
WOW! That would be very interesting to watch. There are several pulse jet videos on Youtube used on model airplanes. I wonder if yours is there.
Yes, like a V1. Runs on ethanol and nitromethane. Drinks fuel fast. Thrilling, but not very practical -- more a curiosity, unless you compete in "jet speed," which I don't. It's an improved version of the "DynaJet" that suffered from weld cracking (http://www.airplanesandrockets.com/motors/dynajet-engine.htm ). I saw one in a hobby shop in the mid-50's, couldn't afford it, but always wanted one. Finally got one when I was in my 50's.

#### Externet

##### Active Member
Something that wasn't mentioned yet is that some coils have an internal ballast resistor.
You don't want one of those.
I will not be using the primary, were that resistor may live. And will likely dismantle it out of the can to remove only the secondary with its core. Even better if I can replace the core with μ-metal. Time to visit a wreckyard and pick several to evaluate for largest number of turns. Never dismantled a 'modern' coil, it may be suitable

#### shortbus=

##### Well-Known Member
Why not a flyback/LOPT secondary from a CRT television then?

#### chemelec

##### Well-Known Member
This Fly Back transformer is 12 VDC in and 10KV out. When Potted in Epoxy.
But is is driven at about 10 KHz.

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#### Externet

##### Active Member
A spool zilion turns would be perfect, I could insert the core of choice but... There is no access to connect to the winding start wire...