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Making HV Plugs And Receptacles From Banana Plugs & Jacks

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jpsmith123

Tue Nov 08 2011, 04:09AM

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

Well I give up trying to buy some decent HV receptacles and mating plugs rated for 50 kv. Not only are they ridiculously expensive, but it seems that in most cases they're not available "off the shelf", thus there's also a minimum buy.

The one thing that many of the commercial parts seems to have going for them (that will be difficult to duplicate without some serious effort), is a "corona-free" design. OTOH, one disadvantage of the commercial parts seems to be that the plug comes as part of a pre-fabricated plug and cable assembly, where the user has to select or specify the length of the attached cable.

In light of this, I can see why Glassman et al. would go the way they did, i.e., using RG-8 coax, a long insulative tube, and some modified UHF connector hardware, for the HV output on their power supplies.

Apparently this (Glassman) method would not be considered "corona free" since AFAIK, as a minimum, the contact point between the center conductor of the cable and the spring loaded terminal (or what have you) at the inside end of the insulated tube, has no special grading or anything and would be open to the atmosphere.

So, is it reasonable to conclude that the Glassman design would have some corona, and that this corona apparently doesn't seriously interfere with the operation or the reliablity of their HV power supplies?

And if so, then fabricating something similar using banana plugs and jacks (of course enclosed and surrounded by sufficiently thick insulating material), and silicone insulated, unshielded wire, seems to me like it should be a viable solution.

I'm wondering, has anyone here ever made any kind of HV plugs and receptacles from banana hardware?

Patrick

Tue Nov 08 2011, 06:06AM

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

I found the bannana plugs in adequate for our purposes, i like to make my own using Porclain and acrylic with MMA adhesive.

Are we 4HV'ers going collaborate and use Femm 4.2 for some common design? Easily reproduciclabe or cheap to sell and trade?

Turkey9

Tue Nov 08 2011, 08:39AM

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

I cobbled together a vacuum feedthrough from banana plugs and other hardware. I took the female receptacle out of the housing and epoxied it into a nylon hose barb so that it stuck out where the hose would usually go. I also had some rubber pieces that were used to cover the connection of a spark plug wire to the spark plug. It happened that this piece fit tight over the hose barb and the male banana plug fit snugly into the rubber piece. This sealed the entire thing and prevented arcing even in a ~100mTorr vacuum. I don't know how well it will work in preventing corona inside, but you never know.

radiotech

Tue Nov 08 2011, 09:13AM

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

The insulative tube was the poly insulation on the RG-8 cable itself. The shield only
went as far as a hollowed out RG-8 plug and socket, and the inside conductor
went straight through with its poly jacket on to its destination.

RG-8 cable itself is good for very high voltage, although it cant be rated as such, because
its connectors aren't.

These is mickey mouse tricks learned in the radar days with pulse modulators.

High voltage cables need to be terminated in 'stress cones' either factory made ones,
or the ones that cable splicers make by certain techniques they use in the field.

Nowadays, the 3M kits are used because the trade of cable splicer is all but gone.

jpsmith123

Tue Nov 08 2011, 01:25PM

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

@Patrick, I think I'm going to start experimenting with FEMM (and other software) as CST has some issues that are really starting to get on my nerves - primary among which is the fact that its own solvers don't agree with each other. And Ansoft Maxwell gives me a solution in between the values that the two CST solvers give me - so I have three solvers and get three different numbers. I can understand slight differences due to varying mesh resolution and boundary conditions, but I think CST has some serious bugs.

@Radiotech, No, the insulative tube I'm talking about is not the PE insulation of the cable itself, but corresponds to it. It's about the same length as the exposed cable insulation and the cable slides into it. Here is an example sold as a kit by another manufacturer:

Ash Small

Tue Nov 08 2011, 05:56PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Could something not be 'cobbled together' using the type of lead that goes from coil to distributor on an automotive ignition aystem?

Either that, or a bit of automotive HT cable, with an unsuppressed plug cap at each end?

I think I'll look into this myself.

jpsmith123

Tue Nov 08 2011, 11:08PM

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

That's what I did for the HV secondary coils I made. I'm using 7mm spark plug wire (silicone rubber insulation with tinned, stranded copper conductors) and Beru connectors. In the range of 10 to 15 kv, the max for the transformer, my simulations predict little or no corona.

OTOH, coming out of the multiplier, where I expect to see 50 to 55 kv, that's where there'll be corona. Unfortunately I don't have any kind of feel for how problematic it'll be. I see numbers right now but that's all.

Ash Small wrote ...

Could something not be 'cobbled together' using the type of lead that goes from coil to distributor on an automotive ignition aystem?

Either that, or a bit of automotive HT cable, with an unsuppressed plug cap at each end?

I think I'll look into this myself.

Patrick

Wed Nov 09 2011, 12:04AM

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

I was thinking porcilain connectors with vinyl aquarium tubing and a copper strand, perhaps filled with soft silicone. you can get polyethylene or vinyl tubing from 1/8 inch all the way upto 2 inches in diameter. On the plus side PE is resistant to UV and Ozone.

jpsmith123

Wed Nov 09 2011, 05:01AM

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

Here's what CST tells me the field will look like along a line (starting at the surface of the conductor and extending radially outward for one inch), for a piece of wire that's representing an 8mm spark plug wire with silicone insulation. The conductor is at 50 kv potential, with ground a few inches away in all directions. Note how just outside of the surface of the insulation the field exceeds the 30kv/cm corona threshold. I don't always trust CST to give accurate solutions, but in this case it's predicting that there'll be corona outside the wire.

Patrick

Wed Nov 09 2011, 05:17AM

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

use femm 4.2 and see if it agrees, we need a accurate, useful field solver. Not a piece of crap... so its imperitive we figure out which one is credible.

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