# Ignition Coils - cheap, quick qnd easy



## Gearsguy

Looking for a good source for coils for your model engines? Here is what I have recently started using. They are cheap, easy to make and extremely plentiful. Millions are just waiting for you in your local junkyards.

They are the COP ignition systems used on all modern cars since the late 1980s. COP stands for Coil-Over-Plug, where each plug has its own coil. They are small, easy to modify for your models and powerful enough to meet most needs.

I bought a set of eight COPs for a 1980's Ford van from a local junkyard for $40 USD. That translates to a mere $5 per coil. If you dont need eight then get a set from a 6 or 4 cylinder engine. I suspect yards that allow you to pull your own parts will sell you one at a time.










The first picture shows a COP just as it came from the yard. The second picture shows it with the boot removed. Remove the boot simply by grabbing and pulling it firmly. Sometimes it may take a slight twist.









The next step is to remove the spring. More rocket science, grab and pull, it will stretch out a bit but should pull off easily. You are now in possession of a basic ignition coil. If you look into the hole where the spring was you will see a flat spade type of connector. This is where you will connect the wire to the spark plug. Look close at the picture and you will see the female connector I used to attach to the wire and which slides over the spade connector. I don't know what they are called but I got mine from one of those electrical connector packs you can get at most hardware stores.

The next picture is the finished coil ready to install. Total time, about ten minutes. Not shown is the wires that come from the electrical source. On the COPs I got the wires were missing so I have to make them. Not a big deal, just a bit if a pain. Be sure when you get yours that you get them with the lead in wires attached. Save some time.

I have experimented with this coil some and found it works with any engine I have and does the job whether 6V, 12V or 9V. I ran an engine at last years GEARS show using 9V batteries. Think I went thru two. It also worked with the low-tension circuit using an Ignitor.

The last picture is the schematic for the transistor circuit I use on all my engines. I do not know who made this design as I was given this many years ago. Works great. If anyone is interested in this circuit I will be willing to cover it in a separate post.






Hope this helps.


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## rmw

I'm interested! This is terrific information - thanks for sharing, and please post about the circuit when you can..
Greg


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## 90LX_Notch

Karma Away.

Good stuff.


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## ozzie46

I'm interested also. Very good info . Thanks


  Ron


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## Ogaryd

I want more info, great stuff! Thanks Gary


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## Billzilla

Gearsguy  said:
			
		

> They are the COP ignition systems used on all modern cars since the late 1980s.



Not all of them, but a fair few for sure. For example the LS series of Chevy V8's still uses separate coils with short leads to each plug.
You also have to check to see if the COP unit has the igniter built into it or it's a separate unit as the wiring is quite different for both types.


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## Gearsguy

Billzillz,

That is good info. I was not aware that some contained an igniter. Can you tell us how to identify the different types? What does the igniter do?


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## Billzilla

Gearsguy  said:
			
		

> Billzillz,
> 
> That is good info. I was not aware that some contained an igniter. Can you tell us how to identify the different types? What does the igniter do?



I'm an engine guy, not an electronics guy. 

The igniter amplifies the signal from the ECU to the coil to make a bigger spark. I'm not sure how to tell if any individual COP has one other than to check the specifications on them. I know the wiring for them is a lot more simple if they do have them integrated as you don't need a separate igniter and associated wiring.


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## Swede

This is very interesting. Years ago, I was deep into coils, and tried a number of alternate sources. The most obvious source (I thought) was small motorcycles, mini-bikes, etc, but unfortunately, almost all of them had electronics potted inside with the coil, and the performance was non-existent, or poor. Then, I tried various small engines associated with lawn and garden equipment, like weed-eaters, and it was the same deal. Some solid state stuff going on in there, and I was unable to make them work well.

If these coils are simply straight coils with no additional potted electronics, it'd be a real boon for us modeler types.

Scrapped outboard boat engines also have these types of coils, one per plug. Unfortunately, my gut feel is that each of them is an individual transistorized ignition. Anyway, I look forward to anyone experimenting with these. They should have good energy for multi-cylinder models.


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## Gearsguy

For several years I was using coils from weed eaters and chainsaws for my hit and miss engines. As near as I can tell they were just coils with no embedded electronics. They worked great. Later I was led to believe that new technology coils had additional electronics embedded in them and would not work. At that time I had access to a supply of older coils and didn't worry about it.

Recently the supply ran out and so I tried winding my own with no success. That is when I started looking for an alternate solution and came across the COP. I did some research on the web and found some drawings of a COP and it looked like there was no embedded electronics so I decided to give them a try. To my surprise and pleasure they worked almost as well as the old chainsaw coils. I think the spark may be a little bit weaker but it definitely works. Perhaps the ones with the ignitor embedded would provide a hotter spark.

I am hoping others will go forward with this idea and document what will and wont work. Even if only some types of COP will work the supply would be huge.

By the way there is another ingition system out there called Coil-Near-Plug which may also be a source for coils. Don't know any thing about them except the name.


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## Ken I

I'm no expert so take this with a pinch of salt - but I have experimented with a few.

If the coil is a two wire (or single wire and earth) then it has no embedded electronics.
If its a three wire (or two wire and earth) then it has an on board ignitor.

The normal coil design can be driven via points and discharge capacitor (condensor) as per a normal old fashioned ignition system or any other system.

The three wire version works by what is a crude but effective system - the third wire is the trigger this triggers an internal transistor which simply shorts the primary - blam - huge spark from the secondary.

There is an internal surge resistor to limit the input fault current - if you use this type of coil on a normal igniton system this resistance gets in the way of the field collapse current to the condensor (or external ignitor) - which will make it a very weak spark generator as Swede has noted. So this kind of coil will only work by triggering its internal ignitor.

The trigger is generally a positive square wave signal of very short duration (less than 1ms) from the engine management system.

I once drove one with a square wave generator with a 50% on / off square wave which overheated the coil in a few seconds - the on board electonics generally shut down on overheat and recover on cooling. (It won't tollerate being shorted 50% of the time.)

The trigger signal must be very short duration otherwise the long short (Huh ?) on the surge resistor causes overheating.

A further caution - in some cases the 12V is supplied to two of the wires permanently (when the ignition is on) in others the ECU turns it on shortly before the trigger signal, this type will overheat with permanent on wiring.

The same sort of thing applies to close proximity single and duplex coils.

The duplex coils have two HT secondaries over a single primary firing two cylinders simultaneously with a waste spark on exhaust.

How do you tell the systems apart (other than the 2 / 3 wire distinction) - measure the three wires on a running motor - find the "power" pair - if it measures less than 12V its being pulsed (you could also use an oscilloscope if you have one) - again a caution the ECU may only turn on the coils when it "sees" the engine is turning.

This doesn't really help when scrapyard delving unless you have determined the type beforehand - perhaps some more knowledgable member could post some further enlightenment.

I tried looking up what vehicles use what systems - like BMW genrally use a 3 wire system - but was quickly confounded by the apparent use of differing systems and even differences from country to country on the same model variant so that route wasn't very helpful.

As pointed out they are cheap and plentiful so grab a couple and play with them.

Ken


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## Swede

How does one test a simple unknown coil without fancy equipment? In the past, I've simply applied voltage across the primary, removed the power (like points opening) and have been rewarded with a nice fat spark. No spark generally = internal solid state stuff. Thoughts?


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## Ogaryd

Hi Gearsguy, Im interested in trying your style ignition system in my new hit & miss engine, could you tell me if you use points, hall effect sensor or reed switch in the diagram posted? When You say cheap, quick & easy, Thats me. Thanks Gary


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## Gearsguy

Gary,

I think you will like this answer. I use paper clips for points. That is one of the great things about the ignition circuit I use. It doesn't need a condenser nor does it need regular points. This is because all you are doing is grounding the base connection of the transistor which turns the transistor on and off. No current, no voltage, no arc.

I am working on another post explaining the circuit, as best I can, and hope to have it up in a day or two.

gearsguy


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## rodue

The transister I purchased from R.S. was not marked  is this apossiblity of 
being wired back ward.
My set up not working. Is there away to check the coil mine seam to be dead  I think.
Rodue


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## lee9966

Since this topic came up again...

This page explains the differences between 2, 3 and 4 wire coils and what vehicles typically have each.  It says Ford and Chrysler typically use 2 wire coils.

http://www.tirereview.com/Article/96901/coil_on_plug_ignition_the_wired_differences.aspx

Lee


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## jasonh

FWIW:

I've been using these after market coils with success.
The original use was for some sort of ATV vehicle.

The common between the hi/lo sides is the iron core.
ie- hook up the points between the iron core and the ground.

It is possible to burn them out if you have a 12V battery and leave the points closed.
You can fix that by using a ballast resistor of about 1 ohm.











http://www.amazon.com/Emgo-24-71532-Ignition-Coil/dp/B00230959C/ref=sr_1_1?ie=UTF8&qid=1350967034&sr=8-1&keywords=6v+12v+coil+emgo


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## rodue

I have a coil that is good now but nothing happening when I hooked it up to schematic.  I know these little components
can take much heat when making a conection. I will keep trying.


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## Ogaryd

I have built 3 gearsguy's ignition systems with used Ford coils,all have performed perfectly. Watch the way the transistor is labeled, some have the letters in different positions. I use a 9 volt rechargable battery and a 9 volt portable phone charger to maintain battery voltage. If the points are left closed, it will deplete the battery quickly.I find the ignition system very dependable.  Gary


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## Philipintexas

Good idea! I've used motorcycle coils but they are not as plentifull and are larger.


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## Niceonetidy

Well chaps, I have looked for a cheap reliable, small compact ignition system for petrol ic engines.  And so far, this is the bet I have found. . . . . . . 

http://www.hobbyking.com/hobbyking/store/__10996__Replacement_CDI_Ignition_for_RCG_50CC_Engines.html

$20 for a complete system including the hall sensor. And they have twin cylinder versus too for another ten dollars. This unit will output three sparks In Quick succession.  I have one here and its going on a friends cnc made engine. I will let you know how it goes. This unit make a big spark !

Cheers

Colin


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## IC-man

Hi all,
About a week ago I found a transistor ign. System using hall trigger that was stated as fail safe in the event of engine stopping with ign left on. I can't find it now. Any ideas where I can find it people.
Thanks All.


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## TonyM

Was it this one. https://www.homemodelenginemachinist.com/threads/a-new-ignition-circuit.20415/ I've built a few of these and they work fine.


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## propclock

Beware the COP primary resistance is VERY low. 
I have cloned the Dave Sage ignition IGBT system for myself and members of
Bay Area Engine Modelers. BAEM. I use the same 5$ coils and they work great.
But I recommend a 4x AA nimh battery supply. They can only supply so much current.
With a BIG 12v battery, you can draw a lot of current. Add a ballast resistor or 
reduce the voltage some way. They can be made quite small if you trim all the excess
plastic/ connectors off. Just my 1.414 cents worth.


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## IC-man

TonyM said:


> Was it this one. https://www.homemodelenginemachinist.com/threads/a-new-ignition-circuit.20415/ I've built a few of these and they work fine.


Hi Tony it looks might it might be the one but can't find the circuit diagram. I have been playing around with many different circuits over the years with various results. I find one of the main problems is the earth has to be really good. Otherwise it blows the P transistor, the hall, or both.
Perhaps I'm being stupid but more help to find the diagram would be useful ( I did notice it has had an update but could find any circuits)
Thanks anyway.
Graham


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## IC-man

Hi Tony,
Thanks for you help I've found it now.
Graham


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## dsage

See post number 63. It's the final circuit. But you might read further down the posts for other tips.
https://www.homemodelenginemachinist.com/threads/a-new-ignition-circuit.20415/page-4

As mentioned above (by propclock) the COP coils need to have current limiting. Either the NIMH battery trick or something like a 5 ohm ballast resistor depending on how much spark you need (less resistance - more spark).


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