Re: Mercotronic Coil Testing

[legendre]

quote Mumbles:

I just picked up an older Merc 200 and one coil reads 500-600 K and has spark while the other coil reads 5.6 K and has no spark.

There’s at least one simple answer, though it might not be entirely correct in this (or another) case.

The winding in question may have broken internally at one point, but continued to run for some time thereafter. The continuous internal arc has created a conductive carbon path between the broken end of the winding and the coil terminal – or between breaks in the winding, in any case.

My guess is that if you actually tried to push more than a little DC current through that 500-600K winding, you’d find that it doesn’t actually behave like a 500-600K fixed resistor.. that is, it can’t sustain any amount of DC current at low voltages as the current path (just a track of carbon) is quite fine and tenuous.

Much like a resistor plug cap that reads open yet continues to spark, it will give dodgy service and will most likely eventually fail entirely.