Re: Glassmike cap as MMC
Terry Fritz, Mon Jun 18 2007, 11:44PM

Hi,

They seem like they might explode and throw glass everywhere.

I have never played with them, but Glassmike and flying glass explosions are almost synonymous in Tesla coil and high RMS current use!!!

Terry

Re: Glassmike cap as MMC
Hazmatt_(The Underdog), Tue Jun 19 2007, 01:57AM

Okay, look, if you don't have the experience with the product, why on earth are you telling someone how it fails???

I have used Dearborn glass capacitors for Tesla Coil use. 5KVDC caps in a string as my pulse network.

They DO work for SHORT run time, but they get warm or hot.

HOW THEY FAIL, for all you people who do not have experience with these capacitors :

They fail this way, The capacitor is undergoing a tremendous amount of stress because its a FILTER capacitor, NOT a pulse capacitor. The dielectric gets hot from the AC current going through them, which causes some swelling of the body of the capacitor. The capacitor is rolled very tight and is somewhat tight in the glass tube, so when it gets hot there is quite a bit of force exerted on the glass tube.
Two or three of the caps in the string will get very warm, and one or two will POP, NOT Explode. Let me be very clear, they will Burst with a POP sound. Glass does not fly far, nor fast, but I did notice a piece of glass about 2 feet away at times. The high viscosity oil in the cap prevents the glass from traveling far.

So now you know.

Limit use to under 10 minutes, limit use to 3 second bursts with 10 seconds between bursts minimum.

Re: Glassmike cap as MMC
Coronafix, Tue Jun 19 2007, 02:14AM

I would class bits of glass 2 feet away as flying glass.
If you can't use them for long bursts because they "pop", explode, whatever,
then why use them at all? And why make such a fuss at correcting a technicality
that is technically correct? If anything, you've made it clear why not to use them!

Re: Glassmike cap as MMC
Hazmatt_(The Underdog), Tue Jun 19 2007, 02:19AM

Goldspehere, When I began Tesla coiling 10 years ago, these were the only economically feasable capacitors to me.

Again, they do not explode, Am I talking to myself here?! They burst with a POP and the majority of the glass falls directly below.

Goldsphere, Explosion infers Bodily Harm. POP or Bursting of MY capacitors in MY Experience (something not debatable here) had little or no chance of bodily harm other then being cut by glass.


You are right that I advise NOT to use these capacitors because they are not suited for Tesla coil use, but if you must use them because its what you can afford, keep them cool in an oil bath in a plastic container.

Another note: You will hear the tesla coil spark gap with a particular 'Bang' and as the capacitors get hot that sound will change very slightly, and if you pay close attention to this you can stop your run short of a burst.

Re: Glassmike cap as MMC
Terry Fritz, Tue Jun 19 2007, 03:02AM

Hi,

Okay, look, if you don't have the experience with the product, why on earth are you telling someone how it fails???

After ten plus years of "having" to "hear out" the complaints about it and a number of injuries..., and noting the trends... and after fighting really hard for five years to push plastic MMCs... I listened, and never bought that crap... I "heard" and "made the art far better"...

I really can calculate capacitor RMS current to less than 1% and I know what most current manufactures "do" and "say" from direct talks in "pleasant and "VERY" unpleasant " situations with them... I helped make the MMc because of older tech explosions and dangers... I think I am sort of an "expert" in this situation...

ANY high power cap in a glass or non safety venting technology these days is just "stupid"... "Glassmike" is infamous for dangerous explosion events... The explosion can almost be calculated to the second...

So don't mean to be harsh, But let's not get anyone else hurt by pushing to many RMS currents into these "glass grenades"... A stupid idea that should be forgotten now... Plastic shrapnel is pretty safe, but the new plastic cap never blow up anyway...

Why even bother with this dangerous and stupid type of capacitor... Thing are much better "now" due to MMCs...

Terry

Re: Glassmike cap as MMC
Hazmatt_(The Underdog), Tue Jun 19 2007, 03:30AM

Say what you will, I have been there myself.

Re: Glassmike cap as MMC
Tom540, Tue Jun 19 2007, 03:54AM

LOL well thanks, I'm not going to use them now. That's kind of what I expected to hear. I did try it out but the coil was untuned and only running of a 60 volt bench supply. They'll probaby still be here 10 years from now, heh maybe some day i'll find a use for them. I did have one crack once from over volting them. I just didn't want to waste any of my good MMC caps on this junk coil im building.

Re: Glassmike cap as MMC
Terry Fritz, Tue Jun 19 2007, 04:05AM

Say what you will, I have been there myself.

Cool!

But I chose to "call you out" on this safety issue...

"Liability" for "dumb remarks" and actions can run into the 100's of millions of dollars... But no one should be "allowed" to get hurt from well known dangers...

Why "defend" that which is "stupid", in light of that which is "bright"... Just because "you" were not killed as a child, does not prevent you from killing other children from promoting old dumb ideas...

We must express the "best thoughts and ideas the best we know them"...

If there is a danger, it is "our duty" as the "knowledge bearers" to deflect those that follow from those well known dangers!!!

In my case, anyting that has to do with "Glassmike" is a danger!!! And I tell all there to just "run away"...

Terry

Re: Glassmike cap as MMC
Hazmatt_(The Underdog), Tue Jun 19 2007, 04:56AM

Terry.... take a minute to read my posts, you might just find that I said Dearborn.

So don't go off on me half cocked.


You can call me out all you like. I speak from experience. I'm not BS-ing anything here.
I myself HAVE 'blown up' 2 Glassmike capacitor and 8 Dearborn capacitors. How many have you 'blown up'?

Take a minute to read where I said I do not endorse their usage, but if you must, use them for very short run times.

Something else, read everything first, then get angry, okay.

Re: Glassmike cap as MMC
J. Aaron Holmes, Tue Jun 19 2007, 06:03AM

I suppose your point is that danger prepared for is not danger at all. Which, whether true or not, is something we must all believe to some extent or we wouldn't be playing with any of this stuff! And, naturally, we all *think* we're prepared when in reality, to be fully prepared would mean knowing the complete domain of possible outcomes. And if we knew that, we'd have gotten bored with all this silly stuff a long time ago!

And I suppose Terry's point is that, if you know the Right Answer, why shoot for any less? Of course, this generally assumes you have some $$ and not a stockpile of "yesterday's" Right Answers. Although hey! That guy on eBay is asking $15 for just one of those caps Tom540 says he's got several of. Time to cash in, perhaps?

For me, time is the most precious resource, so if building something with materials on hand suggests that I'll probably have to do it again when it blows up three minutes (or three seconds!) in, I'll probably wait and save my $$ and build it when I can buy the Good Stuff.

And generally, I'll side with not using caps the are predisposed to self-destruction. No, I haven't used the glass ones, but I have found myself running for my life from a friend's coil when one of his big forty-pound metal-cased pulse caps turned from a cube into a sphere and sent twenty-foot spouts of boiling oil out from the seal around the ceramic bushing on top. One more second under power and I'm sure we'd have all been in the hospital. A positive experience, on the whole, because now we know what *not* to use! There's no shame in blowing stuff up, really. You just don't want to be caught making the same mistakes twice.

Regards,
Aaron, N7OE

Re: Glassmike cap as MMC
sparky, Tue Jun 19 2007, 07:14AM

I had some nasty experiences with some Glassmikes running a parallel series for 30 kV 10nF - the caps got hot and blew shards of glass all over the floor. They just couldn't take the discharge current I'm guessing...
This was years ago - I ONLY use plastic MMCs now!

Re: Glassmike cap as MMC
Coronafix, Tue Jun 19 2007, 01:42PM

MMMMmmmmm, I thought I would be eaten, but I know now who's advice to take, that be the man with the experience. And you pale against few Terry, who think their dark might dost shine brighter.

Re: Glassmike cap as MMC
Wolfram, Tue Jul 03 2007, 08:25AM

Sorry, a bit late, I was going to reply to this thread, but forgot all about it.

I'm surprised that no one has commented the impolite behaviour of Hazmatt.

Hazmatt, why the angry tone? Terry only tried to give safety advice. Just because your glassmikes haven't exploded doesn't mean that glassmikes can't explode in tesla duty, as Terry said, he has heard stories of glassmikes exploding in TC duty.

You are free to challenge his statements, but please try to do so in a civil manner.

Re: Glassmike cap as MMC
Hazmatt_(The Underdog), Tue Jul 03 2007, 08:36AM

Because I think this case is an exaggeration, and what I have seen and done tells me it is.

What surprises me is none of you guys have jumped on the PCB bandwagon yet.

Re: Glassmike cap as MMC
Wolfram, Tue Jul 03 2007, 08:52AM

Still, that's no reason to be rude, you could have just pointed it out.

Re: Glassmike cap as MMC
Hazmatt_(The Underdog), Tue Jul 03 2007, 08:59AM

You know Anders, this is getting off topic by the way, but go back to the first 4 replys and actually read them. I have tried to 'point' this out, but from your point of view and everyone else's, you just don't take the time to read, so I gave up.

Re: Glassmike cap as MMC
Steve Conner, Tue Jul 03 2007, 09:12AM

Will you guys calm down! Terry is *THE* expert on capacitors, period. If you saw the work he has done over the years on characterising different kinds of cap for Tesla coil duty, you would agree.

Also, enough of the arguing over whether things pop, burst, crack, shatter or explode. If things made of glass are doing any of the above, it's unsafe. (well, a potential liability issue at least.) It's also a complete waste of capacitors that would function fine in another project like a C-W multiplier.

The issue with glassmikes is the same as with most other DC filter capacitors, AFAIK. Not only do they have a lossy dielectric, but the lead-outs are simply rolled into the capacitor, or maybe spot welded to the foil in one place if you're lucky. That causes a lot of resistance and very high current density, so they fail where the foil meets the lead-outs, start to arc internally, and the gas generated by the arcing bursts them.

A "real" pulse capacitor has "extended foil" construction where the foil sticks out of the ends of the roll and is connected to the leadout along the entire length of one edge. The path for current is far shorter, thicker, and more even. Low-loss polypropylene dielectric is nice too.