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Large Capacitor Connector

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LAN_403

Proud Mary

Thu Sept 29 2011, 05:15PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

sngecko wrote ...

Thankfully, I will only be using this capacitor as a filter with <2% ripple at 20kVDC. That's only 160mA maximum operating current. So, I think that I can forgo the thermal paste. However, I like the idea of using acrylic tubing on the top. I might then devise a way to "screw down" or use a spring to make the top connection to a bushing lug, or some such kluge.

The corrosion seems to be oxides of copper, as it's got that Statue of Liberty green thing going on.

Given the low currents involved in your application, you might think of soldering directly to the central spigot thingy - which looks like a job for an 80W iron - and then filling the top in with potting compound, or epoxy etc, with or without an acrylic tube 'tower'. Either 25kV TV EHT wire, or old-fashioned vehicular copper-cored sparking plug HT wire would do the job of a flying lead nicely. Completely embedding the top cap connection will also prevent it from hissing off and generating unwanted ozone.

Patrick

Thu Sept 29 2011, 05:28PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

He could also use conductive silver epoxy to make that connection, if he worries about heat, since he said its a PP film cap. Then pot it with epoxy.

Though silver epoxy is expensive, solder is cheap, that cap is a one time find.

jpsmith123

Thu Sept 29 2011, 05:32PM

Registered Member #1321 Joined: Sat Feb 16 2008, 03:22AM
Location:
Posts: 843

That cap was almost certainly built the same way as Kizmo's and subsequently modified. I'll bet that white stuff is ceramic potting similar to the stuff sold by Cotronics.

I'm certain it's a half of a spark gap we're looking at there.

The plastic in the center is machined to increase the path length, and just to the outside of that I see what I think is a groove for an o-ring.

Edit: I bet it was a factory mod done for the laser co.

sngecko

Thu Sept 29 2011, 07:48PM

Registered Member #3447 Joined: Fri Nov 26 2010, 11:10PM
Location: North Jersey
Posts: 97

I really appreciate the comments, especially regarding that unusual connector. Just for the record, the terminal is 5/8" in diameter and 1/4" above the plate, with rounded edges and a slight dimple in the center. The exposed copper plate is 2" in diameter and extends under the plastic flange. The spark gap theory sounds most reasonable to me.

I plan to braze a heavy lug to, or around, the dimple. I'll probably use a blow torch to make quick work of the connection. I'm guessing that the plate presses against the edge of the aluminum rolled inside and, in turn, a poly-something layer that I don't want to get too warm.

Am I right, Kizmo, in thinking that Hi-Voltage Components, Inc. is no longer in business (or bought by another company)? I checked into it a year ago and it looked like it had disappeared a few years back.

Does anyone have a recommended lug (screw-type?) that they like to use for this sort of thing?

Patrick

Thu Sept 29 2011, 09:22PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

I would not braze or flame solder anything to that cap, id use an electric or flame powered solder iron, or you will carbonize the plastic on the cap, and youll never be able to insulate it then.

jpsmith123

Thu Sept 29 2011, 09:40PM

Registered Member #1321 Joined: Sat Feb 16 2008, 03:22AM
Location:
Posts: 843

What about just drilling and tapping the electrode?

Patrick

Thu Sept 29 2011, 09:44PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

Solder the dam thing and be done with it.

sngecko

Thu Sept 29 2011, 10:20PM

Registered Member #3447 Joined: Fri Nov 26 2010, 11:10PM
Location: North Jersey
Posts: 97

Thanks Patrick - I hadn't thought of of that... My only concern now is with mechanical strength.

Since those six holes are still on there, what about (1) soldering a bolt head with the threads up to the nipple, (2) putting an o-ring into its groove in the plastic flange, and (3) attaching an acrylic plate to the six threaded holes with a hole to allow the bolt to pass through.

I think this would sufficiently insulate the electrode without using epoxy potting and provide an added degree of mechanical strength to the pass-thru bolt. Moreover, I could take it apart later.

radiotech

Fri Sept 30 2011, 01:54AM

Registered Member #2463 Joined: Wed Nov 11 2009, 03:49AM
Location:
Posts: 1546

I have some 18 kV capacitors that are about 2 cubic feet in volume. The connectors were PL259
male, but the original insulator and pin were missing. The RG8 cable had the braid soldered to the
259 M plug shell as ground and the insulated center conductor just passed through the connector
body about 9 inches to the capacitor terminal stud.

Turkey9

Fri Sept 30 2011, 02:42AM

Registered Member #1451 Joined: Wed Apr 23 2008, 03:48AM
Location: Boulder, Co
Posts: 661

I'd make an acrylic plate that bolts onto that end using the 6 tapped holes. In the center of the plate but a copper bolt with 2 nuts sandwiching the acrylic holding the bolt at a length that is just slightly too long for the connection. The torque everything down with that o-ring in there.

On a second look at the picture, you might just put a couple washers between the bolt head and the plate to get the right spacing. The bolt can be soldered to without worrying about heating up the cap itself.

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