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Registered Member #54503
Joined: Sun Feb 22 2015, 10:35PM
Location: New Zealand
Posts: 288
GrantX wrote ...
nzoomed wrote ...
Does anyone know much about these russian ceramic caps on ebay? There sees to be tons of old stock doorknob caps on ebay that were made in the USSR, but i dont know how reliable they are, but they also seem to be in rather low values, i need to make a 225nf bank for my MMC.
If I recall correctly, the ones marked "K15У-1" are low loss RF ceramics, and seem to be very popular in VTTC's. I've got a few 10kV 2200pF and 8kV 3300pF examples laying around, but I haven't yet used them as tank capacitors. They seem abundant and cheap, but you'll need a huge pile to reach 225nF.
This site lists some of the common Russian capacitor codes, which makes searching ebay a lot easier:
Thanks ill check that out.
Im building a DRSSTC and am looking for alternative caps, especially now that i would like to up my voltage rating a little, i thik 8KV is a bit on the low side.
Registered Member #30656
Joined: Tue Jul 30 2013, 02:40AM
Location: UK
Posts: 208
As I mentioned in another thread I still recommend looking at using the Aerovox RBPS snubbers (2uF 1kV) - for example 34 (2 parallel strings of 17) gives 235nF at 17kV. Mine ended up about 5 NZD each inc all shipping costs.
Registered Member #54503
Joined: Sun Feb 22 2015, 10:35PM
Location: New Zealand
Posts: 288
Hydron wrote ...
As I mentioned in another thread I still recommend looking at using the Aerovox RBPS snubbers (2uF 1kV) - for example 34 (2 parallel strings of 17) gives 235nF at 17kV. Mine ended up about 5 NZD each inc all shipping costs.
Yes i was looking at that, but they are going to cost me more than the CDE series caps.
Registered Member #1321
Joined: Sat Feb 16 2008, 03:22AM
Location:
Posts: 843
What about one of the metallized polypropylene capacitors from this place:
(I was looking at that 20kv 0.1uF cap for my own possible use, but they're not forthcoming with the specs. for some reason. At a price of $106 USD, it might be a good deal, but without any idea of the peak and rms current rating, max. dv/dt, and inductance, I can't use it).
Registered Member #54503
Joined: Sun Feb 22 2015, 10:35PM
Location: New Zealand
Posts: 288
jpsmith123 wrote ...
What about one of the metallized polypropylene capacitors from this place:
(I was looking at that 20kv 0.1uF cap for my own possible use, but they're not forthcoming with the specs. for some reason. At a price of $106 USD, it might be a good deal, but without any idea of the peak and rms current rating, max. dv/dt, and inductance, I can't use it).
Those do look alright, so ill keep those in mind. Ive just heard back from a local supplier who has a large amount of snubber caps at a cheap price, they are 4.7uf rated at around 750v each, so 21 in series will give me what i need for my bank rated at around 16KV!
I wonder if its worth using less caps to get a higher capacity MMC? I believe people like higher values is there any preferred value people like? It seems people use 375nf quite a bit on their coils.
Registered Member #54503
Joined: Sun Feb 22 2015, 10:35PM
Location: New Zealand
Posts: 288
Ive just managed to score these snubber caps for only $2 NZD each! They are rated at 770VDC so should give me a 225nf bank rated at 16KV if i have 21 in series.
I see their AC rating is only 440V, but it will still be rated at almost 10KV at the AC rating, im not sure what is most important in a tesla coil, but i think i will be sweet.
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
I think the general concensus is to have several strings, and distribute the current evenly between them. How much current can you put through those leads before they get hot and the resistance rises?
Registered Member #54503
Joined: Sun Feb 22 2015, 10:35PM
Location: New Zealand
Posts: 288
Ash Small wrote ...
I think the general concensus is to have several strings, and distribute the current evenly between them. How much current can you put through those leads before they get hot and the resistance rises?
Yes i didnt think much about that at the time, this means i may need more capacitors, how many amps would i expect to go across these caps? My bus voltage is about 680V.
I saw loneoceans had all his caps in series but they are larger doorknob caps, i thought these had heavier terminals on these caps, so i didnt think much about it.
Registered Member #1403
Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968
nzoomed wrote ...
Ash Small wrote ...
I think the general concensus is to have several strings, and distribute the current evenly between them. How much current can you put through those leads before they get hot and the resistance rises?
Yes i didnt think much about that at the time, this means i may need more capacitors, how many amps would i expect to go across these caps? My bus voltage is about 680V.
I saw loneoceans had all his caps in series but they are larger doorknob caps, i thought these had heavier terminals on these caps, so i didnt think much about it.
I do not think you should expect more than 5-10 Arms from these capacitors, peak current is hard to guess, if you know the dv/dt rating it can be calculated.
Do you know about my MMC calculator?
It is a good tool to find out if your MMC can withstand the load/abuse seen in a DRSSTC.
Registered Member #54503
Joined: Sun Feb 22 2015, 10:35PM
Location: New Zealand
Posts: 288
Mads Barnkob wrote ...
nzoomed wrote ...
Ash Small wrote ...
I think the general concensus is to have several strings, and distribute the current evenly between them. How much current can you put through those leads before they get hot and the resistance rises?
Yes i didnt think much about that at the time, this means i may need more capacitors, how many amps would i expect to go across these caps? My bus voltage is about 680V.
I saw loneoceans had all his caps in series but they are larger doorknob caps, i thought these had heavier terminals on these caps, so i didnt think much about it.
I do not think you should expect more than 5-10 Arms from these capacitors, peak current is hard to guess, if you know the dv/dt rating it can be calculated.
Do you know about my MMC calculator?
It is a good tool to find out if your MMC can withstand the load/abuse seen in a DRSSTC.
Ill have a play around with it, i was unsure if it was much use to me since my caps are not on that list and i am unsure of their capacity, what i do know is that the supplier told me a string of 21 would handle 200A easily, I know they far exceed that of a CDE 942 series cap.
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TDK Ceramic "Doorknob" Capacitors For a Tesla Coil
