2024-05-28 Coil Bench Testing

published by dcarver on Thu, 05/30/2024 - 13:06

Forums:

1979 KZ1300 A1 Kawasaki

Installed new YellowSquare ignition coils. Bike still didn't run good.

Time to bench test the coils. Search Google. Find this. Ez pz.

Batt + to coil +
Coil neg to switch to batt neg
Ground spark plug
Hi tension lead to sparkplug cap
Open the switch, primary field collapses, induces hi voltge in secondary, discharges through plug.
But. It doesn't work. No spark. Borrow two auto ignition coils. No spark. Test old Martek coils off KZ1300. These coils had the bike running. But no spark on the bench.

WTFO? Not likely all coils are bad. Must be test set up.

Check all wires for continuity
Check plug resistance
Check switch
Everything checked out SAT

Got to thinking. Auto ignition coils use a condenser to prevent premature point pitting - due to high voltage induced into points. The condenser blocks that voltage.

Installed a condenser and voila, spark.

What I don't know is why adding the condenser enables plugs to spark. Could it be the switch, as it opens the primary to induce field collapse and 2ndry discharge is discharging though the switch contact? Or trying to lit the little bulb in the switch that indicates the circuit is powered?

Here's the test set up.

2024-05-31 Wasted Spark Videos

Permalink Submitted by dcarver on Fri, 05/31/2024 - 11:41.

2024-06-06 Ignition Coil Tester

Permalink Submitted by dcarver on Thu, 06/06/2024 - 15:46.

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.

"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.

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.

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. "

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?