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Registered Member #1875
Joined: Sun Dec 21 2008, 06:36PM
Location:
Posts: 635
True. I guess a clamp is a pretty good idea, now that I think about it... or at least some rubber bands. I'm totally buying some disposable plates tomorrow and trying this out. This was a good thread to resurrect. Maybe I'll put a few under oil and make a bank! It'll be bigger than a normal mmc but saving half a grand on capacitors is well worth it!
Registered Member #2099
Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716
HM_Murdock wrote ... ... If I place weight on top of the plates, the capacitance goes up proportionately. At around 10 lbs it goes up to 8nF, and with about 30 lbs, I show 13.9nF.
I see where Mike used wood glue, so I am thinking of doing something similar with weight applied to effectively remove air and glue it all compacted. With enough weight and some extra glue/sealant, I think it might seal the edges of the plates and also help stop flashovers. My plan is to use this instead of a saltwater bottle cap for my TC.
So, two questions... 1- Will this work? 2 - What would be the best thing to use in this application...silicone, RTV, wood glue, gorilla glue, epoxy...etc...
You want the stack thickness to be small (for high C) and uniform (so every bit of dielectric is doing its fair share of energy storage).
If you use a glue that sets without evaporation or exposure to air (e.g. mixed epoxy -- maybe even low viscosity stuff sold as paint), consider vacuum bagging as an alternative to weights or clamps. With a plastic bread bag, you could squeeze your stack of plates with many hundreds of pounds of force.
An alternative, that could maintain pressure on a dry stack of plates and foil, would be hard flat disks (e.g. 1/2 inch thick plastic or high grade plywood) with multiple C-clamps. The clamps would have little effect on HF electrical performance, if they are well enough insulated. (top and bottom foil layers should be on the same electrical terminal).
Registered Member #3075
Joined: Fri Aug 06 2010, 02:44PM
Location: Athens, GA
Posts: 148
+1 on the clamps idea...
I like the idea of using 2 disks of plywood and either 1 big C-clamp or maybe 2 smaller ones...I am thinking using a few wraps of electrical tape on the clamp will help to keep it from arcing out. I wonder if I shoudl also wrap the sides of the plates in tape to help with arcovers?
The plates are only 6" across, so the wood disks could be cut using my 4.5" hole saw I used for my primary coil mounting board.
The big plus to using the clamp method is I should be able to dial in the C I want from the stack...possibly even fine-tuning it a bit.
I like this idea...if it works, it's less than $3 in materials, and can be re-made in about 30 minutes. It's also not all that bulky, and no messy no liquids or oils involved...I just wonder how much power it can stand up to...I suspect it will be ok with my 9kV/30mA NST...will have to see. Will report back on my findings (hopefully) later tonight.
Registered Member #58
Joined: Thu Feb 09 2006, 05:40AM
Location: Tri-Cities, Washington, US
Posts: 317
From my limited testing, I got it to around 20kV with no problems I'd say, so the NST should be fine. It really all depends on the plates you use. As long as they are the right material, thickness, and good edge rims to prevent arcing it should work well.
Something I've been wanting to see is how well they perform under oil. I imagine you could put quite a bit of power into them under oil with no problems.
Registered Member #2893
Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242
It looks good. With the overhang of the plates flashover shouldn't be a problem. I'm more concerned with the voltage punching through the plates. Polystyrene has a dielectric strength of only 15mV/meter. I'm not sure how thick your plates are. Measure that with a caliper and you should be able to figure out their maximum voltage.
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Plastic Polystyrene Plate High Voltage Capacitors
