MTFCA Forum

I know double spark shows up on a hcct. In terms I can understand, what causes it? How do you correct it and what happens if is not corrected?
I do not have a hcct but I am slowly trying to design and put together in one box a unit with a train transformer, a coil holder to test capacitors and amperage draw and a coil holder to test for bad windings. It will also have a small panel holding an Amp meter to read draw for testing the coils and a voltmeter to read input voltage. I have my plans drawn out, it is just getting it.cut out and assembled but yard work comes first.
I know I can send my coils off to be rebuilt but there is a lot of enjoyment and satisfaction to some of us to do some things ourselves even if the results are not perfect you can learn a lot by trying.

Double sparking occurs because of improper coil point adjustment. The coil points open too earley, close and re-open as the Magnetic field is building up. The first spark fires early and is weak, the second spark fires late and is also weak.

An HCCT measures average coil current as an indirect approximation of time to fire spark. Reasonable results can be achieved if all 4 coils are identical electrically and mechanically. Much more information about coil testing and tuning (Including double sparking) can be found here: www.modeltecct.com.

Check out the webinar video for a broad overview of the Model T ignition system with focus on Model T coil operation. Adjusting coils for equal and consistent firing time by actually measuring firing Time provides optimum ignition performance.

Dennis,
I have basically tried what you contemplating with mixed results. Playing with coils is entertaining to some of us A few suggestions based on my experience are:

A train transformer will not work so well because the frequency is too high. I use 3 or four D cell batteries.

Capacitor testers can be bought for about $20.

Coil winding impedance could be checked with a commercially available meter. I don't have such a meter but have often thought about buying one.

Checking the coils with an ac iron core ammeter connected to a 6 volt dc power supply correlates quite well with an HCCA.

The downside to the above is, double sparking and dwell time are not checked. Professional settings take care of these issues.

Art Mirtes

Hey Dennis,

Just to expand on Mike’s reply. Double spark is caused by incorrect tension/adjustment on the cushion spring. Sometimes this is on brand new points, caused during the process of tuning or the thickness of the material used, depending on the coil type.

I just changed the material thickness and type on Kingston low bridge coils to eliminate double spark and I have a working prototype of Heinze that also eliminates double spark on the ‘11-‘12 style.

This is the fun part about tuning coils is learning the art of it. You can actually hear double spark in any tester, you can only visualize it on a HCCT or StroboSpark, but once you tune your ear to it you will pick up it every time.

Either way a single hot spark will service you better.

David Woods

Williamston T Works

The little book that came with original HCCTs noted that double sparks were OK to have, but then electricity was rather new and not fully understood yet.

An example of a double spark as displayed on a HCCT