Re: TDK Ceramic "Doorknob" Capacitors For a Tesla Coil
Sulaiman, Mon Sept 14 2015, 06:02PM

2.5% dissipation ceramic capacitors worked in a sgtc (Panasonic MDU)
upgrading to 0.1% pp foil/film/foil made a big improvement. (Arcotronics/Kemet A.72)
That was at c220 kHz (unsure/forgot)

ceramic capacitors are a heat dissipation/generation winner
quite lossy but can run relatively hot vs.
pp foil-film-foil generate much less heat, but die at 85C

EDIT: i.e. looks like a reasonable spec. to me but I do not know.

Re: TDK Ceramic "Doorknob" Capacitors For a Tesla Coil
jpsmith123, Mon Sept 14 2015, 07:09PM

Thanks for the info Sulaiman. That at least gives me a reference point.

I think I'll go ahead and buy them...and if for some reason I'm not happy with them in that role, they should work nicely in a Marx generator.

Edit:
Apparently TDK UHV capacitors were used in this "Jolt" contraption (where they were used with a Tesla transformer to generate 1 MV pulses):

So I suppose they are a reasonable choice.

Re: TDK Ceramic "Doorknob" Capacitors For a Tesla Coil
Hazmatt_(The Underdog), Tue Sept 15 2015, 01:22AM

I run TDK caps all the time and they work great.

They do not change over time, and do not short out your transformer. The MICA ones will short eventually and kill your transformer.
Most people shy away from them because of the price tag, usually $20 each, but the savings in construction and better
efficiency in current dumping to me is a plus.

Let's see those scrawny leaded CDE caps compete with M5 threaded buttons for current density! Not even close.

Re: TDK Ceramic "Doorknob" Capacitors For a Tesla Coil
jpsmith123, Tue Sept 15 2015, 02:57AM

Thanks for the info. BTW that's a nice capacitor bank you've got there!

Re: TDK Ceramic "Doorknob" Capacitors For a Tesla Coil
Hazmatt_(The Underdog), Wed Sept 16 2015, 03:25AM

Yea, and you know what, they're really not that hard to build either!

It's just 3 pieces of acrylic bonded together. If you polish the edges with a buffing wheel, it comes out really nice.

Then if you mount all the capacitors and torque them in, THEN glue, it comes out just fine. Try it some time!

Re: TDK Ceramic "Doorknob" Capacitors For a Tesla Coil
jpsmith123, Wed Sept 16 2015, 04:17PM

I have a few novel ideas that I want to try. Maybe later I'll get a chance to make some kind of a drawing and post the details for discussion.

Re: TDK Ceramic "Doorknob" Capacitors For a Tesla Coil
jpsmith123, Thu Sept 17 2015, 01:38AM

Here's my proposed primary circuit: It's a Marx circuit, with the capacitors mechanically (and of course electrically) integrated into the single turn primary. I still have to figure out the hardware.

Re: TDK Ceramic "Doorknob" Capacitors For a Tesla Coil
nzoomed, Tue Sept 22 2015, 11:53AM

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.

Re: TDK Ceramic "Doorknob" Capacitors For a Tesla Coil
GrantX, Tue Sept 22 2015, 01:24PM

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:

Re: TDK Ceramic "Doorknob" Capacitors For a Tesla Coil
nzoomed, Tue Sept 22 2015, 08:53PM


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.

Re: TDK Ceramic "Doorknob" Capacitors For a Tesla Coil
Hydron, Tue Sept 22 2015, 11:42PM

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.

Re: TDK Ceramic "Doorknob" Capacitors For a Tesla Coil
nzoomed, Wed Sept 23 2015, 01:08AM


Yes i was looking at that, but they are going to cost me more than the CDE series caps.

Re: TDK Ceramic "Doorknob" Capacitors For a Tesla Coil
jpsmith123, Wed Sept 23 2015, 06:22PM

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).

Re: TDK Ceramic "Doorknob" Capacitors For a Tesla Coil
nzoomed, Wed Sept 23 2015, 10:11PM



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.

Re: TDK Ceramic "Doorknob" Capacitors For a Tesla Coil
nzoomed, Sun Sept 27 2015, 08:54PM

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.

Re: TDK Ceramic "Doorknob" Capacitors For a Tesla Coil
Ash Small, Sun Sept 27 2015, 09:38PM

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?

Re: TDK Ceramic "Doorknob" Capacitors For a Tesla Coil
nzoomed, Mon Sept 28 2015, 02:15AM

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.

Re: TDK Ceramic "Doorknob" Capacitors For a Tesla Coil
Mads Barnkob, Mon Sept 28 2015, 06:07AM



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.

Re: TDK Ceramic "Doorknob" Capacitors For a Tesla Coil
nzoomed, Mon Sept 28 2015, 11:06AM

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.

Re: TDK Ceramic "Doorknob" Capacitors For a Tesla Coil
Mads Barnkob, Mon Sept 28 2015, 11:29AM

They might be able to handle 200A peak, but certainly not RMS which often is the overseen factor in terms of MMC overheating.

If you open the table with good capacitors, there is a aerovox snubber capacitor, which is more sturdy than yours, try to use those values for comparison.

Re: TDK Ceramic "Doorknob" Capacitors For a Tesla Coil
Antonio, Mon Sept 28 2015, 04:21PM

This circuit looks quite strange. The resistors will dissipate a huge power, the voltage source is too high, and the primary inductance too small.

Re: TDK Ceramic "Doorknob" Capacitors For a Tesla Coil
jpsmith123, Mon Sept 28 2015, 05:32PM

I should've mentioned that those values are basically just "place holders"; although I do plan to use a 50 kv supply to charge the caps. Basically what I want to do is something similar to a "Rohwein" transformer, i.e., a single turn, low-inductance primary winding pulsed at 100 kv, with maybe 30 to 35 turns in the secondary, hoping to get an output of 2 to 3 MV.

Re: TDK Ceramic "Doorknob" Capacitors For a Tesla Coil
nzoomed, Mon Sept 28 2015, 08:19PM


I cant find the datasheet for these caps, but they are quite large and the supplier said they should take high transient currents.
I think the cheapest option for me will be to get more and arrange 3 or more banks in parallel, im not too sure what configuration will be the easiest, but its so cost prohibitive for me to order those aerovox snubbers from overseas.

Re: TDK Ceramic "Doorknob" Capacitors For a Tesla Coil
Mads Barnkob, Tue Sept 29 2015, 06:13AM


What is their physical dimensions? From your picture they seem to fit in a closed hand.

Re: TDK Ceramic "Doorknob" Capacitors For a Tesla Coil
nzoomed, Tue Sept 29 2015, 06:40AM


They are about 60mm wide, to me that was big because i thought they were going to be alot smaller after looking at the photos.

I know they are a self healing type, so thats always good.

The supplier told me each one would be rated at around 25 amps each.

I thought peak current was the thing to worry about not RMS, since the RMS current is always lower than the peak.

Infact, the calculators ive used tell me i should expect 800A peak, but 80A RMS.

Bus voltage is only about 680v max so is alot lower than the 16KV rating the bank will be.

Re: TDK Ceramic "Doorknob" Capacitors For a Tesla Coil
Hydron, Tue Sept 29 2015, 07:53AM

Bus voltage has nothing to do with MMC voltage rating. You need to look at peak current, frequency and MMC capacitance to work out peak MMC voltage - I think the 4hv wiki might have the info, but it's easy to work out from the impedance of the caps at your operating frequency

Re: TDK Ceramic "Doorknob" Capacitors For a Tesla Coil
nzoomed, Tue Sept 29 2015, 09:47AM


I used the calculator that mads has on his site and my MMC voltage works out to 9600v, im not sure if thats peak voltage or rms, but as long as my bank can take 10KV, that should be OK.

Does anyone use microwave oven capacitors?
I can get these for free and they are rated at 1uf, and 2KV i believe, 5 in series would give me 0.2uf at 10KV.

TBH, im not sure how the MMC voltage gets so high with so low bus voltage, with a SPTC, the NST can put put 20KV, so i was assuming that SSTC's can put out the same power because there is no voltage drop across a spark gap.

From what i read, the capacitor will charge up to a higher voltage with each cycle, but i didnt think it could charge up any higher than the applied (bus) voltage?

Anyway, i will need some more caps, i might risk these ones i have for the time being, but im going to need something more capable of higher RMS current. For testing i should be OK on low power, but if im to drive this coil to its max, i can theoretically run the coil up to 1000A i believe.

Re: TDK Ceramic "Doorknob" Capacitors For a Tesla Coil
Hydron, Tue Sept 29 2015, 10:08AM

Remember that the MMC is part of a resonant circuit - a series LC circuit presents a very low impedance at resonance, which lets you drive large currents into it and consequently generate large voltages across the inductor and capacitor.

I wouldn't run too close to the max MMC voltage, but the calculator probably gives peak voltage rather than RMS, so you've actually got more leeway than you thought. 440V * 1.414 * 21 = ~13kV.

I'd recommend you try and do the calculations of this stuff yourself - the MMC calculator is very useful but it's important to understand why it gives the results it does. The understanding will help a lot when you're later trying to get the coil to run, or deal with a problem. Also it could be worth trying to simulate a coil - LTSpice is free, and though it's a bit of work learning how to use it the skill will be very useful if you keep up with electronics as a hobby/profession.

Re: TDK Ceramic "Doorknob" Capacitors For a Tesla Coil
Justin, Tue Sept 29 2015, 12:52PM

Microwave oven capacitors are not suitable for many different reasons.

Re: TDK Ceramic "Doorknob" Capacitors For a Tesla Coil
nzoomed, Tue Oct 20 2015, 04:18AM

Ive just ordered my CDE 942 series caps, 40 of them (5 in series x 8 in parallel) this will give me a bank rated at 10KV which should be sufficient if i pushed my coil up to 1000APK.

Anyway, ive been browsing alibaba, and i know these are chinese, but for the price, they should be worthwhile testing for tesla coil use, since the manufacturer claims they are suitable.

Sometimes the stuff out of china is not always that bad, IDK, but im interested to try them, these are rated at 60A each!





There are many other types listed there also, im interested if anyone has experimented with chinese caps.

Re: TDK Ceramic "Doorknob" Capacitors For a Tesla Coil
Mads Barnkob, Tue Oct 20 2015, 06:18AM


Your MMC plan sounds fine for 1000A.

About the Chinese capacitors... Package Type: Surface Mount

Their datasheet seems to be specified for 1kHz/10kHz, I would like to see atleast some 100kHz figures. and

They do specify Dissipation factor: Geasured at 1000±20 Hz AND 25±5℃. When Cr≤1.0µF， 4×10-4； When Cr>1.0µF， 6×10-4, the characteristics of polypropylene is rather linear, but only up until 80kHz, then it starts going up.

A proper field test is surely needed but on the other hand, the pricing is just around where you can find proven surplus caps.

Re: TDK Ceramic "Doorknob" Capacitors For a Tesla Coil
nzoomed, Tue Oct 20 2015, 10:47AM



Yes i agree field testing is the only way to know for sure.

There are countless other capacitors on alibaba too for various prices.

If you know of any suppliers of eurofarad doorknobs, im keen to know. They seem to be thin on the ground.
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Re: TDK Ceramic "Doorknob" Capacitors For a Tesla Coil
Hydron, Tue Oct 20 2015, 03:09PM

Big plus with the chinese is shipping is normally reasonable to places US sellers are too lazy or charge too much to ship to (e.g. NZ).

Could be an interesting option for mid sized coils, (~1kA peak), where a single series string might work okay for a rather low total price.

Aliexpress is probably easier to deal with if anyone wants to give it a go!

Re: TDK Ceramic "Doorknob" Capacitors For a Tesla Coil
nzoomed, Tue Oct 20 2015, 09:25PM


Yes i agree, i didnt see those particular caps on aliexpress, but there is alot to choose from.
Would be great to see some reviews on them, shipping from china is so cheap its not funny.

I need a couple of aerovox snubbers and the shipping is going to cost me 3 times as much to get them here to New Zealand!

There is also tons of cheap variacs on alibaba, (not all chinese, some are from india)

I know most chinese variacs are crap, but if you buy a larger one than what you plan to use, you might get away with it.

Re: TDK Ceramic "Doorknob" Capacitors For a Tesla Coil
Hazmatt_(The Underdog), Wed Oct 21 2015, 01:09AM

For a few dollars more each, you could buy capacitors that will not burn up, EVER.




Anything with a high uF value in that form factor is going to be a rolled film capacitor, which will eventually fail.

That's just my opinion though.

Re: TDK Ceramic "Doorknob" Capacitors For a Tesla Coil
nzoomed, Wed Oct 21 2015, 03:29AM


Those capacitors in your link are far too low for tesla coil use, i would need tons of them to build a decent MMC around 0.25uf, in fact even if i had the money, i wouldnt fit that many caps on my coil.

Interestingly, the eurofarad doorknobs are rolled film also and are rated at only 2KV each, so lets assume these chinese caps only realistically can rate up to 2KV and not the 4KV they claim, then you might get somewhere with them, who knows, they might work better than you think.