Originally Posted by Ken Tee
Charming! Pot calling the kettle black? I didn't say anything about the "insulation on the LT wires" and I wasn't thinking at the time about any inter-layer potential differences because, as you agree, there wouldn't be any; instead I wrote of the "insulation around the LT winding." Yes, one place where that sees a large electric field with your test is between the copper of the innermost LT layer and the cross-piece of the bobbin. Another place is between the copper of the live LT tail and the channel in the bobbin wing along which it runs.
There is no need to get your back up. If ever I answer a different question than the one you intended to ask, all you have to do is to point that out. The wording of what you wrote in your previous post is consistent with the same misunderstanding expressed by someone else in a question in a subsequent post, the answer to which I provided. Fine that you say this isn't what you meant.

Originally Posted by Ken Tee
What I admit I don't understand, however, is:
[*] given that you didn't know how the armature had been wound, and given that insulation around the LT winding that can withstand, say, 1 kV long term would be perfectly adequate, why do you apply 2.5 kV with the consequent risk of blowing your friend's armature's insulation.
As I've written in a few places, I had no way of knowing if this coil had been properly wound, or if it had been vacuum impregnated. If it had been properly wound, there would be a layer of insulation around the core of the armature that easily can withstand 2.5 kV. If not, my test would have destroyed the coil and I would have had to spend a day winding a new one.

Had the coil been directly wound on the armature, and even if it had been vacuum impregnated, not all of that resin might have made its way as far as the first layer of windings. In operation, those windings are subjected to a cyclic electromagnetic force as the armature rotates, and relative motion caused by this force can and does abrade insulation from windings. Even if the coil passed my other tests, there still would be the non-negligible possibility it would fail due to this abrasion after some unknown number of miles.

Even though the coil already had passed one dynamic test with a Merc-o-tronic tester, that test cannot determine if the primary was improperly wound directly on the armature. Again, the reason for doing this test is a properly wound coil will pass it, and an improperly wound one will fail.

Originally Posted by Ken Tee

[*] given that slip rings see 6 kV in operation, and given that slip rings can exhibit faults only when exposed to voltages higher than 2.5 kV, why do you conclude that a slip ring that passes the 2.5 kV test is good.
My experience is that no slip ring has passed this test but failed in operation. The resistance was 10 GOhm (i.e. ten-thousand-million Ohms, to emphasize the point) at that voltage, and either the resistance would have had to fall by many, many orders of magnitude between 2.5 and 6 kV to fail (which is physically implausible), or something in the slip ring that survived 2.5 kV would have to suffer dielectric breakdown at 6 kV. Amongst the many things I might worry about happening on a magneto, this is way down on the list. This is why I concluded it was good.

Originally Posted by Ken Tee
[*] given that your insulation tester has a crocodile clip that you could have clipped directly onto the live tail of the LT winding or the earth tail, why do you go to the trouble of winding a length of stainless steel wire around the slip ring and then connecting your insulation tester's crocodile clip to that. (It just struck me as a very odd thing to do.)
I do it this way because it simultaneously tests whether there is insulation on the armature and whether the operating surface of the slip ring has a sufficiently high resistance so as not to be a concern. Attaching the tester to either of the primary coil leads wouldn't test the latter.

Originally Posted by Ken Tee
given that you have an Eisemann tester at your disposal, why use an insulation tester on the slip ring at all.
Already answered.

Originally Posted by Ken Tee
On the point about environmental testing of our condensers, you originally wrote, as if it were fact, "no extended environmental testing has been done on them." Our own two main test bikes have clocked up tens of thousands of miles without any degradation of their EasyCaps. We have sold many hundreds of EasyCaps, and we're unaware of even a single failure of an EasyCap in service to date. That is environmental testing, in a real-life environment, ozone and all.
As I wrote previously, there is a long and checkered history of condensers that have been sold with seller's written assurances as strong as the following: "Modern substitute, very high specification, zero failure." Despite that seller's unqualified assurances of not a single failure, an unreasonable percentage of them failed in service. I have no way to confirm your own claim that there hasn't been "even a single failure" of yours, nor do I even care. What I do know is I have enough legitimate concerns about your capacitors, some of which I have expressed, not to have any interest in relying on them myself.

However, an important point is, it is not up to someone else to demonstrate your capacitors do have problems in service. It is up to you to provide credible test data to indicate they do not. Having them sit in a pan of hot water for a day, or telling us that they have had zero failures, is not sufficient.

Originally Posted by Ken Tee
Looking at the alloy and steel that are exposed to this ozone, I'd have thought that these levels of ozone are insignificant. But if they are significant, I am surprised that the eminent physicist Dr. Falco didn't mention the ozone issue in his article previously referred to. Did he do any ozone tests on the Panasonics, do you know?
I'm not going to take the time to look for the quote, but at least one treatise on magnetos explicitly comments on the importance of not sealing the points housing because of the buildup of ozone levels. That's why even a Lucas Wader magneto has a way for water to get in -- in order to let the ozone out. When a capacitor is placed in the cavity at the other end of the armature, the reactive ozone created by the points, or any of the brushes, has to make at least a few right angle turns in contact with metal to get as far as the condenser, which itself is covered by epoxy as well as its own coating. In contrast, your condenser is directly adjacent to the points, where the ozone level is highest, and not protected by anything other than itself.

Originally Posted by Ken Tee
On the ESR point, the simplistic model of a real capacitor being merely a perfect capacitor in series with a perfect resistor is, as far as I can see, totally insufficient to describe the faults that are found in magneto capacitors. One fault is the inability to hold a charge. I can't see how that can be modelled with an ESR, but without an EPR (equivalent parallel resistance). Another fault is dielectric breakdown. I guess an EPR and ESR might perhaps be able to model that at one particular operating point, but not over a wide range. Anyway, that's by the by. I was just puzzled by what Dr Falco had written.
The simplified, not "simplistic," ESR model was used in an article in a motorcycle magazine to explain to that audience the essence of why Lucas wax paper condensers failed with time. This present thread is about restoring a c1920 Bosch magneto, and has nothing to do with failure modes of various condensers. However, since so many types of replacement condensers touted by so many people over the years have failed, I included a sidebar about capacitors because I believe it is important for people reading this to understand why I used the one I did in order to have high confidence it would survive long term. You have not reported any tests on the capacitors you sell that would be needed to give me the necessary confidence to even consider using them.

At this point I think we have covered capacitors in far more detail than anyone reading these posts cares to know about them, so please direct any future questions to any aspects of this restoration other than capacitors. I'll be happy to discuss any and all issues, other than why I don't use the capacitors you are promoting.

Last edited by Magnetoman; 10/10/12 2:58 pm.