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Large Capacitor Connector

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sngecko

Wed Sept 28 2011, 03:54AM

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

I recently purchased a large 2uF, 25kVDC capacitor for use as a filter in a laser power supply.(After all, it came from a dye laser power supply). Everything is going swimmingly except that I can't find a connector for the high voltage connector.

The rolled poly-something cap is a cylinder some 17 inches tall and about 8 inches in diameter. The base is the ground connector with several tapped holes for mounting and connection, while the top seems to be a copper plate with a 1/2"diameter nipple in the center without threads or obvious standard connector.

I'm hoping that someone here recognizes this type of cap. I was hoping for something more elegant than a 10A spring clamp to make my connections.

Herr Zapp

Wed Sept 28 2011, 05:09AM

Registered Member #480 Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644

sngecko -

A photo of this interesting termination would be useful .....

Herr Zapp

sngecko

Wed Sept 28 2011, 03:20PM

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

Thanks, Herr Zapp. I should have this morning, but I didn't have pictures with me. Here are a couple:

Here is a picture of the top half of the capacitor and the connector I tried to describe earlier. It may be a common connection for energy storage capacitors...

Herr Zapp

Wed Sept 28 2011, 05:09PM

Registered Member #480 Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644

sngecko -

Normally, the terminals on energy storage capacitors will have high-current threaded studs or bolted flanges capable of carrying peak current of 1,000's of amperes.

The small cylindrical stud exposed on the top end of your capacitor doesn't appear to me to be the primary terminal. More typically, these HVC capacitors have a flat flange plate bolted to each end.

Surrounding the central stud are a series of six tapped holes; are these electrically connected to the central stud? If so, your capacitor may just be missing its flange plate.

What does the bottom terrminal look like? Just a flat flange plate? Please post a photo.

Herr Zapp

sngecko

Wed Sept 28 2011, 06:01PM

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

There certainly is a missing top piece, but that lug, and the surrounding copper, is the only electrically connected location on the top. This model of capacitor is no longer made, so I can't just get one from the manufacturer.

The threaded holes are just that, with no connection between themselves or the lug. I've attached a picture of the bottom plate. I also noticed that the oxidization of that top copper lug reduces electrical conduction unless I scratch into it just a little bit with my multimeter probes.

Patrick

Thu Sept 29 2011, 02:52AM

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

Im suprised it has two different ends, there usually the same, your sure theres no conductivity between that center nipple and metal threads? Maybe that corrosion is preventing your continuity test from revealing the real connection?

Proud Mary

Thu Sept 29 2011, 02:58PM

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

I am guessing that the machined base is for direct chassis mounting, via an electroconductive thermal grease to diffuse current 'hot spots'.

The top with its concentric lips and bevels (to increase surface tracking distance, I suppose) looks like a propriety HV connector - but Heaven alone knows what!

If it were my problem, I'd try to find some bits of acrylic tube that fit the concentric rings, and perhaps glue them into place once the electrical connection had been sorted out.

What is that corrosion on the top metal surface, and what caused it?

sngecko

Thu Sept 29 2011, 03:19PM

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

After checking again, I found no connection among the 6 top threads and the top copper plate.

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.

jpsmith123

Thu Sept 29 2011, 04:04PM

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

It looks like it was made to attach directly to some kind of a spark gap switch. That "stud" in the center, with its rounded edges and eroded center could be one spark gap electrode. It's hard to tell from the picture but it looks like it could be a copper-tungsten alloy of the type commonly used in spark gaps. Also that would explain the groove in the plastic; i.e., it's for an o-ring.

Kizmo

Thu Sept 29 2011, 04:51PM

Registered Member #599 Joined: Thu Mar 22 2007, 07:40PM
Location: Northern Finland, Rovaniemi
Posts: 624

That capacitor looks very familar :)

0.33l beer can for size comparison. Mine is 20kVDC 3ÂµF. It has flat terminals on both ends.

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