[cliffyk]

I apologise, as an older fellow dealing with some annoying health issues I get "snippy" at times...

Here is the post:

I have been pondering ways to make a practical device for testing COPs, under actual operating conditions, for some time; and a couple weeks ago while looking at a sales flyer from an electronics supplier I have dealt with I ran across the perfect core component. I had seen this device in the past but as it is decidedly "old-hat" it had slipped my mind (gimme a break, I'm old).

Here's a photo of the complete set-up, and a WMV video of it in action--I will provide details below:



Click here to watch the WMV (if you can't see the sparks download and play the file, your internet connection bit-rate may be too slow to see them).

The core component, with the heat sink in the center of it all, is a Velleman Electronics K2543 CDI (Capacitive Discharge Ignition) driver module that can be had as a kit from Arcade Electronics for $20.31 (currently on sale).

This kit is designed to retrofit a classic Kettering (points/condensor/coil) ignition system to a CDI driver, however it can also serve here to drive a COP when a simple normally open momentary contact switch is used to simulate the distributor points.

I have also used an Am-Pro T71240 adjustable spark tester that I picked up someplace several years ago for less than $10. Any similar unit would work.

Shown in the photo and video is one of my five remaining good Accel COPs, none of the 3 bad ones will fire at all even though they all check out OK with a low voltage Ohmmeter.


If anyone is interested I will draw up an interconnect schematic, it works quite nicely to test an individual COP, or to compare a set.

[stal94gt]

what? you lost me with big words

[sharkbait]

Can you just pull it out and stick the spark plug in it and set it on something metal. Then just crank the car?

[cliffyk]

Originally Posted by stal94gt what? you lost me with big words

Originally Posted by sharkbait Can you just pull it out and stick the spark plug in it and set it on something metal. Then just crank the car?

Sorry to bother you with this "overly complex" mechanism/method to gauge a COPs maximum potential output...

[FoxHoss]

never mind? i was gettin into that

[sharkbait]

I find it interesting just a tad more complex then it needs to be though

[cliffyk]

Originally Posted by sharkbait Can you just pull it out and stick the spark plug in it and set it on something metal. Then just crank the car?

Aside from that it is difficult to crank the engine and observe the spark, doing that will not let you gauge a COPs extended gap performance, which is 110% related to it's overall condition.

I have a set of Accel COPs, of which 3 failed within 15k miles and within a period of two weeks. Of those that failed all test out OK using the typical low-voltage Ohmmeter tests (0.8 to 2.0Ω primary, 6k to 8kΩ secondary), however one will not fire at all with the DIY tester and the other two will not fire at more than a 0.1" gap with the adjustable tester.

A good OEM COP will fire a 3/4" gap on the adjustable tester.

This setup wrings out a COP, and can in fact burn one out in short order if you make it fire 20-30 times in rapid succession with en very wide gap. If a COP can fire a 1/2" or more gap then it is OK. if not then even though it can fire a normally gapped plug, and passes low voltage resistance tests, it is toast.

[FoxHoss]

i dont find it complex at all, its rather simple when you break it down. I like this, i may make one myself.

What are you using for the power source?

the way you have it set up, with the adjustable spark tester, you could probably compare the actuall strength of the spark that is put out by the coil, in theory proving and aftermarket coil to be stronger vs a stock coil and vise versa? right?

EDIT: i gotta say i like this write up. not many people talk about coils, perhaps the boost-a-spark system, but thats about it

[cliffyk]

Originally Posted by sharkbait I find it interesting just a tad more complex then it needs to be though

High voltage plays by the same rules as low voltage circuits, however that it is HV pushes conductors and insulation to the edges, Therefore testing HV circuits at low potentials is pretty much a wasted exercise.

The tester described test the COPs at levels that are 200% to 300% of typical duty cycles, in fact as I said before it's easy to burn one up using this tester.

This is why 50+% of the COPs returned to Ford, under warranty repairs, have nothing wrong with them. There's a TSB to this effect...

[cliffyk]

Originally Posted by FoxHoss i dont find it complex at all, its rather simple when you break it down. I like this, i may make one myself. What are you using for the power source?

It takes 7.0A or more to properly saturate the coil, on the bench I am using a Tenma 14A 12V supply, for most their car's battery would be a good source.

the way you have it set up, with the adjustable spark tester, you could probably compare the actuall strength of the spark that is put out by the coil, in theory proving and aftermarket coil to be stronger vs a stock coil and vise versa? right?

YES, that is why I was pondering and put together the system.

One caution however, as COPs never in real use fire at their "potential" (15kV to 20kV is the probable max) it is quite possible to burn out even the best COP by making it fire at it's full potential more than 5 or 6 times every 10 minutes or so. In fact I burned out one of my remaining Accel COPs doing just that with this test device.

EDIT: i gotta say i like this write up. not many people talk about coils, perhaps the boost-a-spark system, but thats about it

Thank you!

[cliffyk]

I had a question on another forum as to the voltage being generated in the video. The breakdown voltage of air at STP is around 33kV/cm, and in the video above the gap is about 0.55", or 1.4cm.

So the voltage being demanded of the COP is 46kV or so--this was just about the maximum the Accel COP could deliver consistently.

[Trick Tuners]

I applaud your creativity, but there is a much easier way to test a COP if you have a datalogger. Simply watch the fuel trims while you unplug one at a time. Or you could watch the missfire counters at WOT. There is one problem with your device, it should be under pressure. Its much harder for a spark to jump when there is a lot of air pressure around it. I'm not sure if this math is correct, but assuming 100% VE and 14.7 psi with 9:1 compression it would need to fire under 132 psi (at WOT). But you could "simulate" the pressure by extending the gap.

[FoxHoss]

Have you had a chance to test other coils for comparison? ie, a FoMoCo coil?

Granted you don't really want to be burning them out.

I agree about the spark being under pressure. The pressure adds resistance which is being delivered via the adjustable spark tester, if you could equate the distance the spark travels to a pressure equivilant value

[cliffyk]

Originally Posted by Trick Tuners I applaud your creativity, but there is a much easier way to test a COP if you have a datalogger. Simply watch the fuel trims while you unplug one at a time. Or you could watch the missfire counters at WOT.

This will only show that the COP is capable of firing a normal plug gap. It does not allow observation of a COP's maximum potential output, on a bench top under controlled conditions. Nor would it reveal a degraded output--indicative of a failing coil.

There is one problem with your device, it should be under pressure. Its much harder for a spark to jump when there is a lot of air pressure around it. I'm not sure if this math is correct, but assuming 100% VE and 14.7 psi with 9:1 compression it would need to fire under 132 psi (at WOT). But you could "simulate" the pressure by extending the gap.

Adding a pressure chamber to house the gap would be a somewhat trivial task, however as you have said it would add nothing that simply extending the gap cannot.

In the video the gap has been extended to 15mm. In air at STP it requires 33kV/cm to ionise the gap between pointed electrodes--so the output of the COP in the video is approximately 33kV * 1.5 = 50kV.

----------------------------------------------
Just to add some background info so we can dispense with the condescension, I hold a MME (MIT '73) and among many other assignments worked with HV ignition systems in industrial thermal deposition and heating applications for several years in the mid 70's.

[cliffyk]

Originally Posted by FoxHoss Have you had a chance to test other coils for comparison? ie, a FoMoCo coil? Granted you don't really want to be burning them out. I agree about the spark being under pressure. The pressure adds resistance which is being delivered via the adjustable spark tester, if you could equate the distance the spark travels to a pressure equivilant value

I have not tested other coils at this time, though I plan to. I would add that this is not an inherently destructive test method, nor is there any risk in damaging a coil if the tests are conducted with appropriate duty cycle.

Not doing so can damage the DUT, so just don't do that.

In my posting above I added that ionisation of an air gap at STP requires approximately 33kV/cm, and that with the 15mm gap used in the filmed test this indicates an output of at least 50kV. As I had adjusted the gap to just below that at which the coil would not "fire", this is a\n acceptably close indication of the COP's maximum output.

The pressure issue, as you and others have suggested, is largely irrelevant for bench testing the coils to determine their maximum potential; because as long as the test conditions are maintained the only effect would be to shift the absolute magnitude of the observed value (in this case the maximum gap across which the DUT can spark). The comparative relationships would remain effectively unaltered.

[jonwrong]

Great work!

[Trick Tuners]

Originally Posted by cliffyk The pressure issue, as you and others have suggested, is largely irrelevant for bench testing the coils to determine their maximum potential; because as long as the test conditions are maintained the only effect would be to shift the absolute magnitude of the observed value (in this case the maximum gap across which the DUT can spark). The comparative relationships would remain effectively unaltered.

I would love to see these results!! Just be sure to record the temp and humidity at the time of testing, and if possible, control them to within a few % for easy comparison.

[cliffyk]

Originally Posted by Trick Tuners I would love to see these results!! Just be sure to record the temp and humidity at the time of testing, and if possible, control them to within a few % for easy comparison.

I only have six (still working) Accel COPS (<20k miles), and the stock COPs from my '03 GT with 80+k miles on them.

Temp and humidity are easy as I do the testing in my climate controlled electronics lab (see photos below), 72°F (+/- 1.5°) 50% to 55% RH.

I tested four of the Accel COPs, and four OEM units (the driver's side as they are the easiest to pull, here is what I found:



If I run into other COPs I will test them (or if anyone has any they'd like to have tested--let me know).

I went through two sets of Weapon X COPS in less than 5k miles in July and August. They had serious issues with long drives (50+ miles) where they would misfire badly once they got heat soaked. When attempting to start the engine after a short stop, after a run on the highway, they would not fire at all and I had to wait 15-20 minutes for them to cool.

The Weapon X people were great to deal with--after the first set failed they sent me another, after that failed they provided a full refund. I have had no such problems with the stock coils.

Here are a couple photos of my lab:

North end:


South end:

[Trick Tuners]

Great info! Thanks for sharing. I'll keep on telling people that the stock COPs are better then most aftermarket COPs. (until you prove me wrong)

[cliffyk]

Most all, maybe all, COPs that look like the OEM units are made by a company named Micro-Tech. The Ford stock COPs (I disagree with their assertion of a "high failure rate") are made by them, as are Granatelli's.

Also though I have no links to verify this, the body of the Accel COPs, other than being yellow, is identical in every way to the OEM coils--if they were not made in the same molds, then the molds were dead ringers of those used to make the OEM units.

These are all made to the ordering vendor's specs of course, with regard to price point, and other factors--I am certain that if I wished to order a significant quantity I could get them in green...