Pinpointing Insulation Failures in Coil

[marmas]

Can you provide any way to pinpoint the location in a coil where the turn to turn short is occurring. This coil is a 12ohm automotive (12V system) coil (0.140 diameter wire). I've read about Surge testing but it seems to only indicate the presence of a turn to turn short but does not have the ability to identifiy the exact location. Thanks.

 

[GusD]

Hi marmas

All you said is valid.The surge test would not apply itself very well to an automotive ignition coil.
As for telling where the short is located I don't think you find an instrument to do that very easely.
I don't know what you plan on doing after you find the short.If you plan on repairing the coil,it is not impossible to do it, but it might be cheaper to buy a new one.If you cut one of this things open,I believe you probably will know what I mean on buying a new coil.They are messy.

GusD

 

[marmas]

Thanks Gus. This coil is a fuel injector coil that has failed in the field in an injector and I'm looking to perform failure analysis to try to determine how this turn to turn short was created. The coil is overmolded in nylon, tested and then assembled. The coil was tested and passed at a certain resistance limit but went low when it was placed in an injector. My problem is that when I try to remove the nylon to inspect the coil, my process also removes the poly insulation. Thus, I needed to find the precise location of the defect so I could selectively remove the nylon.

 

[electricpete]

You might try energizing it and viewing and infra-red image.

 

[OperaHouse]

We used to send a pulse down a line and look at the reflection. That works with coax finding a crimp or a short and it might work with a coil. This would tell you how long the wire was before the problem. This would tell you about what layer the short occured since you have the imformation how they were made. The only way to pinpoint it would be by IR heat immage but the plastic coating would make that difficult.

 

[CarlPugh]

With AC you can open an AC clip on ammeter slightly and run it over the surface of the coil. The shorted turns will have high circulating current and will read much higher.
Can you test the coil with AC?
It may be possible to use a DC clip on ammeter to determine which part of the coil is shorted? (low magnetic field)

 

[gcaudill]

I have heard of a test where the part is placed in a salt water bath. A small current is passed through the coil. A certain chemical is added to the bath. If there are any dielectric failures in the wire the chemical will turn pink at the point of failure. The problem is, I can't remember the name of the chemical. Do some research on pinhole testing in magnet wire.

 

[jbartos]

Suggestion: A Time Domain Reflectometer (TDR), or Frequency Domain Reflectometer (FDR) or Standing-Wave Reflectometer (SWR) might be applied. Visit

http://www.thomasregister.com

and type Reflectometers under Product or Service, which will return 30 companies to approach to. Skip optical reflectometers.

 

[ScottyUK]

Thinking along jbartos' suggestion, TDR's also show up under under descriptions like cable fault locator and are usually fairly easy to hire.

They usually need to know what type of cable in terms of C and L in order to determine distance, or have a set of curves pre-plotted for different cable constructions. Do you have a good coil to compare against which you might compare the damaged one?