What insures voltage balance on stacked pairs of PS Filter Caps?

[Chuck H]

It's happened to me! Anything black has the potential to be conductive. It's just a question of how much "black" was used to make a thing black. Because all black pigment is carbon. Packed tightly enough "lamp black" as it is known, and still the main component for making anything black, can align conductive pathways within the black thing. Especially bad are black items intended to be heat stable. As carbon is already in it's heat altered state I suppose bumping the carbon up to the level of a structural component of the mix could be the case. Just guessing on that though. But I can tell you darn certain that automotive vacuum tubing is conductive! Or at least it can become that way and more so when HV is applied to it! It's a not so funny story involving smoke and some burned up components

[tedmich]

silicone o-rings are safe! but ugly orange usually...

[Chuck H]

Yes. I've taken to testing many potential construction materials for conductivity! FWIW I wouldn't automatically trust BLACK silicone O-rings, I would test them. Pretty much anything that isn't black and not otherwise made of a conductive material is safe. After that it's a matter of longevity and thermal stability. Silicone rates pretty high.

[Leo_Gnardo]

I can tell you darn certain that automotive vacuum tubing is conductive! Or at least it can become that way and more so when HV is applied to it! It's a not so funny story involving smoke and some burned up components

At first I thought you were using vacuum tubing to make a sort of engine "stethescope" and got a spark-plug jolt to the ear. Glad to hear that wasn't the case.

O-rings dammit, ya just can't trust 'em. First frozen ones sent the Challenger into oblivion, and Dr. Feynman had to prove it to the congressional investigation committee while the blood drained out of the faces of Thiokol Corporation's top brass. Now electrically conductive o-rings have been playing hob with nevetslab's power supplies. FWIW carbon black isn't by far the only black pigment, but it is the cheapest so you'll find it nearly everywhere. Good find Chuck! Now I'll never be tempted to assume an ordinary o-ring is an insulator.

[Chuck H]

Carbonized something or another is used as the black pigment in nearly everything but dye's. And even some of those. I don't know of any black pigment that doesn't involve lamp black or some other form of carbon. I think there were some ancient Asian inks that used graphite, but that's only almost black I'm open to any new information I can understand though.

"Lamp black", incidentally, is so called because of the black soot that would build up on glass oil lamp covers. And the same basic principals are used to make it today.

[nevetslab]

I was fortunate to have escaped without failure and smoke trails, no doubt due to Hewlett-Packard's attention to details in their multiple feedback loops to safely control this complex high voltage regulated power supply. The imbalance I found initially was again present as soon as I re-installed the Nichicon caps, with the SOMEWHAT CONDUCTIVE O-Ring glued to the base of the cap, used for mechanical stability (as I had to spread the leads out further). I powered it up this time at 20VDC output, and looked across the pair of ballast resistors, finding again that huge imbalance. Shut it down, removed them, then took the ohmmeter to the O-Rings to find variable resistance. That explained it. No solder mask present on the 1970 vintage PCB of the HP power supply. So, still needing the 'false-bottom' the O-Ring provided for spreading the leads out, I cut, punched & fitted fishpaper insulators to solve that problem. I still have to finish up with the trim adjustment to the supply's Constant Current Comparator circuit which had a failed resistor, but was saved from larger headaches. Task for later man.

[nevetslab]

OMG, the original "dim bulb tester."

I've never heard this one called that before. Sure you're thinking about the same instrument? The 1617A I have is the 4-terimal Capacitance Bridge, covering the range from a couple pF out to 1.1 Farad, has a 0-600VDC bias supply & leakage current test range from 20mA down to 60uA full scale. Basic RC bridge, 120Hz internal generator. I had to look at the schematic to see if there was any internal incandescent bulbs besides the pilot, Bias On and DC Charge Present bulbs on the panel. Light grey finish, flip-top cover, AC Mains powered. Bigger than their 1650B Impedance Bridge.

[g1]

I've never heard this one called that before.

Pretty sure he was referring to SGM, aka "helpy helperton", aka "the honey wagon".

[Chuck H]

Great. I was eating cereal! Now I have to clean milk off of my keyboard!!!

[Enzo]

Oh nevetslab, thanks for making my day.

The guys are right, I was refering to the "guru" who posted above somewhere. he likes to feign expertise by making stuff up, or by - as in this case - responding to something not asked. SO I was making a pun on the "light bulb limiter" we use around here a lot. But it is also called a "dim bulb tester." So I was inferring that that individual was himself a dim bulb when it came to testing things.

So i am sure your test equipment is fine.


Unless you are in fact pulling my leg, in which case I just totally swallowed the bait.


In any case, welcome to the forum.

[R.G.]

We had a saying back at my former day job - some bulbs are so dim that they suck the light out of their surroundings.