Re: A Tale of Two Condensers

[legendre]

Now on to a new instrument.. this time, a Heath IT-28 Capacitor Checker. As of this late date, the IT-28 is pretty well obsolete, but it does have one very useful set of functions – a highly sensitive leakage test at actual DC operating voltages from 10V up through 600V.

Each condenser was, in turn, connected to the test terminals, the voltage was set to max. (600 VDC) and it was left to settle for five minutes at which point the leakage characteristics were observed. Rather than a typical analog meter movement, the IT-28 uses a green ‘Eye’ tube as an indicator: Eye open = no leakage / Eye closing or closed = leakage.

White – no leakage observed at any voltage.

Green – initially no leakage at 600V, but within a few seconds the eye began to close. By the time five minutes had elapsed, the eye was fully-closed. Then the voltage was progressively lowered one step at a time, taking note of any leakage. Significant leakage was found all the way down to 350V (fully closed) and showed moderate leakage one or two steps below (~200V range).

Conclusions? If White is to be accepted as a standard (it seems reasonable), then Green is most certainly defective. Interestingly, Green’s failure mode suggests that when in-use, it may give acceptable spark at cranking speeds – for instance, when checking for spark – yet cause a great deal of trouble once the engine has started and run for a minute or two. Bear in mind that Green was once part of a magneto that ran one of my TD20 just fine..

Again – and this is a salient point: Green was apparently working just fine in one of my TD20 motors, though my second TD20 never ran right with Green in the magneto. What is the source of this apparent discrepancy – was Green the culprit, or simply part of a larger issue?

Either way, Green’s a piece of crap, it was most recently in my troubled TD20 motor, and it’s not going back in there. (What if all that grief was caused by a condenser with a sneaky little failure?). In any case, I have new parts on the way.. so we’ll see what, if any effect, they have on the running quality of bogey TD20..