Topic: DIY coil tester

[Deltarider]

I've noticed that often coils are being replaced without diagnosing. So I've looked around for a simple DIY coil tester and finally - on a Spanish site – did I find a diagram to my liking. You will find the scheme, adapted somewhat by me, below.
Needed is: a 12VDC source which could be your bike's battery, a condenser like the one on your bike, a 5 pins changeover relay and some wires. Cost in total: < € 5,-. 
The tester works and even better than I had expected.

1) For a 12V source I have used a 12V/1.5A adapter that is normally connected to my penlites charger.
2) In my test I have used both an OEM condenser as one from an electronics dump (see pic). Both (630V/0.22-0.26 μF) worked fine. For the OEM one, polarity is probably to be observed. For the ordinary one that I had lying around, polarity doesn't matter.
3) A 12V 5-pins changeover relay can be had for less than € 4,-.
4) Coil: in my test I have used the OEM dual output TEC coil we know. To complete the circuit with such a coil, oppose the ends of the HT leads at a distance of say 7-8mm of each other (see pic). For testing a single output coil the end of the HT lead needs to be opposed at a similar distance to GND ofcourse.

As said, the tester performed well. Out of curiosity, I've done some measurements to find out in how far this set up mirrors our bike's ignition.
VDC: 12V
Current: 0,6A
I have held probes of an automotive DMM on the coil's negative and GND and measured:
Tach: 3780 RPM
Duty Cycle: 71%

Remarks
To fully test an ignition coil, you want to run it say for 10 minutes continuously. I have no idea if a changeover relay like mine will survive this. The condenser takes most of the brunt ofcourse. Bosch states their relays are good for up to 250.000 cycles, so who knows (mine is not a Bosch).
For a complete test, have the plugcaps and sparkplugs attached. The threads (or hexagons) of both sparkplugs need to be connected like in one and the same vise grip or similar device. Enjoy the ozon!
Warning 1: be aware there is high voltage involved.
Warning 2: when you have the HT leads end in a piece of vinyl tube like shown in my pic, the sparking may eventually burn a hole in that tube.
Prospect
This is a very simple device, but it works. You can make it as nice as you want, put it in a case, whatever... I myself just used wires and alligator clips (see pic).
This could be a first step. Next level would be to have some electronic trigger instead of a mechanical relay; not an expensive pulse generator but something simple, like a solid-state relay.
Any recommandations?

[MauiK3]

That's pretty cool, do you have a video of it in action?

[Deltarider]

That's pretty cool, do you have a video of it in action?

Yes. Click that last line in the attachments. It's a mp4.
Here it is once more.

[Deltarider]

And another one.

[scottly]

As said, the tester performed well. Out of curiosity, I've done some measurements to find out in how far this set up mirrors our bike's ignition.
VDC: 12V
Current: 0,6A
I have held probes of an automotive DMM on the coil's negative and GND and measured:
Tach: 3780 RPM
Duty Cycle: 71%

First, the two coil outputs are the opposite polarity, so placing the HT leads apart from each other is not a good test. Say the output voltage is +/- 8000v, then there is a potential of 16,000v between the leads: each lead should have a gap to ground.
Your numbers don't add up: if the duty cycle was really 71% and the voltage 12V, the current should be 1.7A. Perhaps the actual duty cycle is 29%?
Here are pics of my ignition tester, which can vary from zero to to 10,000 RPM.

[Deltarider]

Thanks for your reaction. Your setup is ofcourse ideal: almost all aspects can be monitored.
The duty cycle was measured at the correct spot, simarly to the coil primary's NEG or where it's wire is fastened to the breakerpoints, if you like. Realise that 'at the breakerpoints' although static you will see 12V, dynanically(!) things are going wild so to speak. If you're interested, you can make a simple tester with a diode, a capacitor and a voltmeter that can read 600VDC.

Say the output voltage is +/- 8000v, then there is a potential of 16,000v between the leads: each lead should have a gap to ground.

Uhm... I have to think about that a bit more.
I was surprised myself the current was lower than the 0,8 - 1,3A I had expected. I did all measurements similar to how I do them on a bike. I'll repeat the test with plugcaps and sparkplugs attached and will run it for a longer period of time. The reason I didn't do that now is, that I fear the sparking between the bare ends of the HT wires will erode them badly and these wires are already a bit short  . As soon I have caps and plugs in position, I will do some further measurements and then also with a common ground. Also I would like to know what temperature the coil develops when 'running'.
I still study the possibility of a solid state relay.

[AshimotoK0]

This is my solid-state coil tester.

I will trace out the circuit. The signal generator  could easily be substituted with a cheap 555 timer PCB of eBay. It uses a dedicated ignition transidstor to switch coil.