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Bench Testing Ignition Coils 2 weeks 4 days ago #32566

  • dcarver220b
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I applaud the enthusiasm to learn, but feel I need to curb your actions before you damage your coils. 

First- The KZ1300 has a redline of 8000 rpm, so the spark event needs to happen in 60 seconds divided by 8000 = 7.5 milliseconds.A spark event is the build up of a magnetic flux, collapsing of the magnetic flux and a discharge of a spark.A typical spark duration for most ignition systems is around 1.3-1.5 milliseconds and there are some ignition systems capable of up to 2.8 milliseconds but for the purposes of this rant, let’s stick with 1.3 milliseconds.So if a spark event at 8000 rpm is 7.5 milliseconds and 1.3 milliseconds is used up in spark duration, they the time left over to build a magnetic field is 7.5-1.3 = 6.2 milliseconds. So the ignition coil has to be able to charge in 6.2 milliseconds or less. Most ignition coils running a 3.0 Ohm primary circuit require 8 milliseconds to build a full magnetic flux.To achieve a full magnetic flux of 8 milliseconds and a spark duration of 1.3 milliseconds (9.3 milliseconds total) works out to 6457 rpm. After that there’s not enough time to create a fully charged spark.So where am I going with this? – The coil is designed to build a full magnetic flux in 8 milliseconds.Energizing the coil for longer than 8 milliseconds will not build any more flux and can likely damage the windings by overpowering for too long. Your setup with a toggle switch should be reconsidered as it’s impossible to turn on and off in that timeframe.

Hmm.. Hopefully I’m doing the math correctly here.. If coil primary is charging (putting winding under stress) every 6.2 milliseconds, then discharging (winding not stressed) for 1.3 milliseconds then the primary winding duty cycle is 79%. 100-(1.3/6.2*100) A 3 ohm resistance at 13 volts draws 4 amps (13 volts / 3 ohms).  I’m simply having difficulty understanding how a 1 second power toggle could harm the primary winding. 

Second- You measured the resistance of the components but do you have the design specs for the coil??Measuring resistance will give you one of 3 outcomes. Either the resistance is within spec or too low or too high. If you measured the resistance and found it out of spec and to the low side, it could mean in the case of an ignition coil, that the winding is short circuited and if so, it will not build a full magnetic flux. It’s unlikely that you’ll ever measure a coil with high resistance. You might measure a primary winding with an open circuit but it would be a rare event. It would depend on where in the coil the winding burnt out. 
With the Martek coils, I don’t have baseline data. However, I do have 3 coils, and all measurements across all 3 coils is very close. I would think this establishes a confident point of reference.

Third- A condenser acts like an accumulator. It accepts a charge and will also dissipate a charge. In the case of a points operated ignition circuit, when the magnetic field collapses, it also collapses on the primary winding and creates a voltage on the primary side equal to 1 volt per winding. Most primary windings are in the neighborhood of 150-200 windings so the voltage created by the field collapsing can be around 150-200 volts. That voltage is absorbed by the condenser and then once the voltage in the primary windings drops below the 150-200 volts, the charged condenser offloads it’s charge into the primary circuit and that can extend the duration of the spark slightly, but the purpose is to discharge that energy before the points close and help reduce the electrical load across the points. Your setup less the condenser should create a spark although I would caution you not to toggle the switch too many times for fear of burning out the primary windings. I suspect a short in the primary windings are why your test is not working. Usually, a standard test for coils involves a setup similar to yours, but instead of using a switch, the positive wire end is momentarily tapped on the battery terminal which limits the “on time” to something more appropriate.

Yes, for DC, a cap is a storage device. I’ve seen video of point ‘arc’ with and without  the condenser. It’s significant!
  
I can toggle the switch about once per second and never leave the primary ‘on’ for longer than that. The primary resistance for all 3 of the coils is right at 3 ohms as measured with a Fluke 87.And the fact I do have spark when the condenser is connected proves that the primary is intact.

What I’m not understanding is why… why when the condenser is in circuit, do I get a nice big fat blue spark but no spark when condenser is disconnected?

I have a set of used FJR 1300 coils I’ll try next. I have baseline data for them, and they were working well when replaced. 

The web has several examples of pulse width modulator coil testers.. that allow simulation from 600 to about 6k rpm. About 70 USD. I've also seen some home-brew circuits using 555 pulse timers, SCR's etc. Or, thinking out loud, I bet my neighbor has an old distributor that could be hooked up. Science!

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Last edit: by dcarver220b.

Bench Testing Ignition Coils 2 weeks 4 days ago #32568

  • Neville
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Interesting topic! My understanding is that the capacitor (sometimes called a condenser in this application) is critical in providing a rapid change in current through the primary windings (12V circuit) of the coil.  Without the capacitor, there is a less rapid change, as when the primary circuit is broken, there will be siginificant sparking at the point where the primary circuit is broken, reducing the rate of change of current.  As we all know, the secondary (high voltage) output from the coil is a function of the rate of change of current in the primary windings.  f you use a conventional switch to open the circuit, you are unlikley to see the amount of ionisation or sparking when the switch is opened .
I recall back in the 70's and early 80's when most vehicles used contact breaker ignition systems, that if a car was difficult to start on a cold morning, adding a very large capacitor (about the same size as the coil!) across the contact points (using a couple of crocodile clips) would provide a much more powerful spark and get the vehicle started - once started, it could be just unclipped without any issues.
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Bench Testing Ignition Coils 2 weeks 1 day ago #32589

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The quest continues. I found this tester - but not sure if it will work on a wasted spark coil?

Found this one too which looks more promising ...




 

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Last edit: by dcarver220b.

Bench Testing Ignition Coils 2 weeks 1 day ago #32590

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First off, I should say Thank You to KB for his detailed response. Thank You!

Spent too much time today looking for an ignition coil tester. From KZ1300.com, KawBoy commented my testing tecnique is flawed and I'm possibly damaging the coil from over-charging the primary.

While searching the innernet, found a video where a guy explained that ignition systems require very short primary coil charge time (see KB comment above!). Which is why his coil tester was needed... as it would provide a pulse width modulated signal to the coil with ranges of frequency and dwell time appropriate for coils.

Ok then, maybe that explains why I could only get spark when using the switch and condenser, and no spark when when contacting the test lead directly to battery (w condenser still in circuit).  See video above. The switch was/is getting 'iffy' on opening and closing, perhaps the shortened open time plus charging the condenser and resultant condenser fast release time got into the coil's happy zone of millisecond charging/discharging and thus produce  a spark?
 

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Last edit: by dcarver220b.

Bench Testing Ignition Coils 2 weeks 1 day ago #32591

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Found this tester - and ordered it.. 

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Bench Testing Ignition Coils 2 weeks 1 day ago #32592

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..and, if anyone is interested found these videos on wasted spark ignition systems.. 2024-05-31 Wasted Spark Videos Permalink  Submitted by  dcarver  on Fri, 05/31/2024 - 11:41. 
  1. Really good explanation of wasted spark system
  2. Spark plug tester without electrode
  3. Ignition Myths - GREAT video!
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