*POP* Goes the Condenser

[Todd, KA1KAQ]

The mystery is solved, at least partially. The noise that resembled a plastic 2 ltr soda bottle being run over was caused by a detonating oil-filled condenser. It blew the top off the metal can after deforming it pretty nicely. Sure does explain the puddle, and the cooking smell that became noticeable yesterday.

But why? I was under the impression that these things hardly ever went bad. The bigger mystery will be figuring out why it let go, as being 'defective' should've show up decades ago.

Beyond blowing oil and a bit of paper around the inside, it doesn't look like anything else was damaged. Haven't checked the schematic yet to see what's associated with it. Maybe a rectifier shorted or something else failed that took it out?

So much for blaming Frank for spreading vicious crapout rumors.... 

[N3DRB The Derb]

Derb, I'll just be happy to work you on the air again - regardless of the rig! Of course, by the time you get back on, my rig will probably crap out. You just know it will, I'm overdue.... 

wow, you predicted that crapout within a day!!!!! 

pretty good splat. 

what rig was that in and how much joltage did you have on it?

I have a 1930's GE Pyranol 15uf @1000 vdc I am debating on recycling into the new HB rig. is clean with no leaks. Gotta test it.

[WQ9E]

Todd,

They almost never fail but "almost" is an important qualifier.

Years ago at a contest station I was using a nearly new Alpha 77 which had a rather spectacular oil filled cap explosion.

For the older capacitors, I am aware of at least two failure modes.  One is where the seal has failed and the oil is hygroscopic and its dielectric strength is reduced through moisture absorption, additional corrosion may also come into play here.  The other mode is when one foil plate finally moves enough (after numerous heating and cooling cycles) to contact either the opposing plate through insulation breakdown or the container side. 

But oil filled caps are still pretty darn reliable although they are at least as messy (probably more so) than electrolytics when they do fail spectacularly.  I don't have any experience with them but I imagine there have been a number of failures of the modern "energy storage" oil type caps when pushed hard.  These caps were designed for large energy discharge and some heat up pretty quickly when exposed to high ripple and most require voltage de-rating when used for filter service.

Rodger WQ9E

[k4kyv]

I think I have had two oil caps crap out in all these years.  None of mine exploded.  They just shorted out. 

A couple of others have  sprung leaks and some oil dripped out. I remember sealing the leak in one with epoxy and going on using it.

The hazmat nazis wearing their space suits would have a heyday cleaning up yours, Todd, and charging you $5000 for the job.  They might even insist on hauling the entire rig to the hazardous waste disposal site, since it has been contaminated with PCB.  That would add additional 5 or 10 grand to the clean-up bill.

The Kentucky EPA called me to find out what I did with the oil caps in my BC1-T. I told them I had repaired the transmitter and was using it, and that seemed to satisfy them.  The radio station that gave it to me had to account for disposing of the PCB.  Several components that were not even oil filled had those yellow stickers affixed.

Which rig was it, the KW-1?

[Todd, KA1KAQ]

Yeah Derb, except I figured it would end up being the LV transformer since it's a notorious weak link in the transmitter and has leaked tar in the past. Gotta get a SS sub for that white-hot 5Z4 metal tube.

Fortunately (?) it was only the 32V this time. Pleasantly surprising is the location: easily accessible with the rear plate removed, held in place with two mounting screws and two screw terminal posts. The 32V series is notorious for having the parts that break located under layer upon layer of 'stuff'.

This one is C305, a .25MF according to the schematic, but listed as 25mf in the parts list. It's paralleled across L303, the 5 hy HV Filter Reactor and in line with the pair of 5R4GYs.

I beat the hazmat guys to the draw, Don. Already cleaned up the oil, planning to blow some WD40 through the inside chassis later to clean up the excess inside. It covered pretty much everything in there with oil. Just wish I'd gotten a shot of the smoke escaping, it was most impressive resembling a wildfire.

Should add that I may have pushed it over the edge by having the rear switch for the HV transformer switched from the 600v to 700V position. The manual says that the final drives more efficiently at the higher voltage even though the tube manufacturer recommends 600v for fone. The symptoms certainly showed up in the last two days while running it at the higher tap.

Most likely route for now will be to replace it, then check voltages once a known-good replacement is installed. It's a pretty stout unit, so it's still a bit surprising to see how it expired. Hopefully it's just the condenser. Derb will be on the air before me though, since my stock is still up north.

[WQ9E]

I have a feeling those choke tuning caps face pretty rough duty but you did get a lot of life out of it.  I am sure the smoke was most impressive!

Earlier this year the motor run cap on my Delta dust collector blew apart with flames and smoke.  I was running some glued up panels through my drum sander and heard a pop from the dust collector but assumed it was just a small chip of wood from one of the other power tools finally getting sucked into the collector area; having ear protectors on made what was probably a big bang sound pretty minor.  A couple of moments later the dust collector shut down and smoke begin covering that area of the shop.  That got my attention since there is a lot of sawdust in the vicinity but fortunately it was just the capacitor shooting out the remains of itself along with some burning oil.  At least all of this was in the barn so it wasn't a big deal.  This cap was only a few years old but unlike your Collins cap it was another proudly produced piece of **** from Red China.

Rodger WQ9E

[Todd, KA1KAQ]

Sounds like I'm in good company!

The one thing I forgot that might tell more is that C-305 let go right after I unkeyed the mic. Was turning the rotation over to Tom and looking forward to enjoying a chat with him as it's been a while, but as soon as I let go and the receiver recovered, *pop*. Hadn't buzzarded too long, but obviously it had heated up enough.

Heading out now to check the other garage where a few boxes of parts reside. Most are still up north, but there may be something usable out there. Otherwise I'll be chasing DX for a while on the heels of WB3HUZ, the DX Cannon. 

[Opcom]

Derb, I'll just be happy to work you on the air again - regardless of the rig! Of course, by the time you get back on, my rig will probably crap out. You just know it will, I'm overdue.... 

wow, you predicted that crapout within a day!!!!! 

"and calleth those things which be not as though they were. "

[W3SLK]

I seem to remember workin on our PPI HVPS on ship. They had non-polarized caps that were made out of glass and sealed ends. You could actually see the oil inside and were designed to be refillable. I think one of the 'cycle' PM's called for checking the color of the oil and changing it if it had turned dark. I know damn well they were PCB's since these units first saw duty in ~1964/65 era. They were Sprague Vitamin Q's.

[WA1GFZ]

Todd,
Maybe you had raw AC on the cap due to a rectifier failure.

[Todd, KA1KAQ]

I did wonder about that, Frank. Haven't checked the tubes yet, but I've got a box of JAN 5R4GYs somewhere here, so they'll get replaced even if they still test good. Wondered if maybe one shorted.

Got the pieces out, it's amazing how distorted the top and can are. The terminals that were parallel now sit closer to 45 degrees. The can itself bulged so much that it's nearly oval shaped now. That was some serious pressure build up.

.25 mfd @ 2000 VDC is stamped into the can. A friend locally may have one in his parts unit.

[WQ9E]

Nice carnage Todd!   

Take a close look at the 5R4 sockets and tube bases, they are prone to developing carbon tracks between pins given the voltage differential between fairly closely spaced contacts and this could be a source of AC hitting the filter. 

There is a good reason most rectifiers used for plate supplies have the plate connection on top.  It doesn't take much dust to create problems with the 5R4 series and I have run into carbon track problems with both my Viking 1 and 32V-1.  Fortunately the only parts replacement needed was a pair of sockets (and the tubes) in the Viking 1.

Rodger WQ9E

[flintstone mop]

I thought I recognized the crowded space of your 32V?
A TX that puts out 125 watts and modulates without a sweat, but a bad mechanical design for maintenance.

I worked for Howard, W3HM taking in the basket cases for a Summer and it was not goodness when he had a 32V for repairs.


Fred

[Todd, KA1KAQ]

Or 'after and before' works too, I guess. Got the 32V replacement condenser from Nick K4NYW today and installed into its mounting bracket after reforming the bracket, which was deformed when the old condenser bulged and exploded. Compared to the 'expanded version', it sure does look different!

[k4kyv]

If you are looking for good quality condensers, check these:

http://www.v-cap.com/tefloncapacitors.html

For the voltage and capacitances you need, you might have to purchase several and run them in series-parallel. 

Be sure to scroll to the bottom of the page for pricing information.

[w8khk]

Gee Don, after looking at the prices, I had to check my calendar.  Thought it was April first again    Good one!  Thanks for the laugh!