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MMC where to buy

billybob

Active Member
That's usually because they find just the right capacitor to make up their resonant tank cap which is convenient. This is definitely the most difficult part for me when I'm building a Tesla coil - finding a resonant capacitor. It's still difficult for me to this day.
Aghh It's so frustrating! It's the last part of my tesla coil (besides the control box) and also the hardest to find and get. Someday though I WILL FIND SOME!
 

DerStrom8

Super Moderator
Aghh It's so frustrating! It's the last part of my tesla coil (besides the control box) and also the hardest to find and get. Someday though I WILL FIND SOME!
Now that I think about it, this is precisely the reason I never finished my own medium-size Tesla coil - I got stuck on the cap bank and then life happened, and I ran out of time :p
 

billybob

Active Member
Now that I think about it, this is precisely the reason I never finished my own medium-size Tesla coil - I got stuck on the cap bank and then life happened, and I ran out of time :p
I can't let that happen!!! Ive spent too much time and money on this to be stopped by a few capacitors!!:arghh:
 

billybob

Active Member
I even got a variac for the project
 

DerStrom8

Super Moderator
I can't let that happen!!! Ive spent too much time and money on this to be stopped by a few capacitors!!:arghh:
Well as long as you don't plan on getting married, buying a house, changing jobs, and having a child in the near future, you're in a better position than I in terms of spare time! ;)
 

rjenkinsgb

Well-Known Member
Most Helpful Member
Would these be suitable? Epcos B32654A1154J000 "high pulse" rated polypropylene caps, 150nF, 1600V DC, 27.5mm lead spacing.

RS Components are selling them rather cheaper than any other place I can find; £0.84 + VAT but you have to buy 200, which makes the total cost almost exactly £200.. Part number 194-3738

They are not quite a match for the Cornell Dubilier 0.15uF 2000V ones that some people online are using - but those seem to be nearer £5 each!

The description in the RS item page is wrong, it says 0.47uF - but all the list entries correctly say 0.15uF for that part number, eg. here:

More info in the Epcos datasheet, they are on page 20 for the specific part:
 

DerStrom8

Super Moderator
Would these be suitable? Epcos B32654A1154J000 "high pulse" rated polypropylene caps, 150nF, 1600V DC, 27.5mm lead spacing.

RS Components are selling them rather cheaper than any other place I can find; £0.84 + VAT but you have to buy 200, which makes the total cost almost exactly £200.. Part number 194-3738

They are not quite a match for the Cornell Dubilier 0.15uF 2000V ones that some people online are using - but those seem to be nearer £5 each!

The description in the RS item page is wrong, it says 0.47uF - but all the list entries correctly say 0.15uF for that part number, eg. here:

More info in the Epcos datasheet, they are on page 20 for the specific part:
My concern with those would be the current rating. The 942C20P15K-F capacitors from Cornell Dubilier are selected by Tesla Coil enthusiasts because their peak current rating is 432A (WOW!!!). I am not able to find the peak current rating in the datasheet for the EPCOS parts.

That being said, I have seen capacitor banks made up of these caps, but that was for a small Tesla Gun, which uses a QCW driver. If I'm not mistaken, this is much less taxing on the capacitor bank in terms of current rating requirements. I have yet to build a QCW coil though.
 
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billybob

Active Member
My concern with those would be the current rating. The 942C20P15K-F capacitors from Cornell Dubilier are selected by Tesla Coil enthusiasts because their peak current rating is 432A (WOW!!!). I am not able to find the peak current rating in the datasheet for the EPCOS parts.

That being said, I have seen capacitor banks made up of these caps, but that was for a small Tesla Gun, which uses a QCW driver. If I'm not mistaken, this is much less taxing on the capacitor bank in terms of current rating requirements. I have yet to build a QCW coil though.
Ah thats too bad
 

DerStrom8

Super Moderator
That's not to say they can't be used, the MKP style of capacitors are great at high frequencies. It would just take more parallel strings to split up the current, and that will greatly increase the number of capacitors required to make a suitable MMC.
 

billybob

Active Member
What about these? They say they are 2000k volts
Need to calculate how many I'll need if they work.
 

DerStrom8

Super Moderator
What about these? They say they are 2000k volts
Need to calculate how many I'll need if they work.
You'll have to link the actual product page, you can't share shopping carts that way.
 

rjenkinsgb

Well-Known Member
Most Helpful Member
From the info contained in the data sheet, voltage vs. frequency, they are rated to stand 9.5A RMS continuously at 20 KHz.
The maximum pulse charge or discharge rate is 1000V per uS.

I'm sure there must be a way to calculate the current for that, but it's not a calculation I've ever needed!
>google<
For a constant current to give a certain rate of change, the formula appears to be:
V(t) = (I*t)/C

From that, if I have it correct, 1000V per uS on a 0.15uF cap means it is rated to handle 150A ??
 

billybob

Active Member
What about these? They say they are 2000k volts
You'll have to link the actual product page, you can't share shopping carts that way.

I determined that 8 would work for a 9k 60 mA power source. With almost enough power rating
 

DerStrom8

Super Moderator
Those also don't give a peak repetitive current rating. Again, they're MKP which is great, but without knowing how much current they can handle it'll be a gamble.
 

billybob

Active Member
Those also don't give a peak repetitive current rating. Again, they're MKP which is great, but without knowing how much current they can handle it'll be a gamble.
Hmmm and the price difference isn't a significant difference. Guess I'll keep looking
 

DerStrom8

Super Moderator
Another cap you might want to keep your eyes open for are the Aerovox RBPS20591KR6GNZ IGBT snubber caps, 2uF/530VAC. Those are the ones I used on my DRSSTC. They are absolutely spectacular, with an individual peak current rating of around 900A. You will need quite a few in series to meet your capacitance requirements, so cost may become a concern, but if you're able to find a good deal they will handle the high current quite well. I bought 50 of them for $1/ea back in the day, though last I checked the price went up significantly. Due to their high capacitance you would need over 100 for your coil (110-120, somewhere in there). There are other caps in that series that may be worth a look as well.

 

billybob

Active Member
Another cap you might want to keep your eyes open for are the Aerovox RBPS20591KR6GNZ IGBT snubber caps, 2uF/530VAC. Those are the ones I used on my DRSSTC. They are absolutely spectacular, with an individual peak current rating of around 900A. You will need quite a few in series to meet your capacitance requirements, so cost may become a concern, but if you're able to find a good deal they will handle the high current quite well. I bought 50 of them for $1/ea back in the day, though last I checked the price went up significantly. Due to their high capacitance you would need over 100 for your coil (110-120, somewhere in there). There are other caps in that series that may be worth a look as well.

Why do some have more than 2 prongs?
 

DerStrom8

Super Moderator
Why do some have more than 2 prongs?
Most likely they're designed to be mounted on a PCB, so individual pins are needed, but impedance needs to be reduced so they use multiple pins. My guess is that all of the pins on one side are connected to the same point internally.
 

billybob

Active Member
Most likely they're designed to be mounted on a PCB, so individual pins are needed, but impedance needs to be reduced so they use multiple pins. My guess is that all of the pins on one side are connected to the same point internally.
oh ok
 

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