# Finally starting on my coil...

#### Usernametaken

##### New Member
This is what dining tables are for, right?
Going to be asking a LOT of questions in here so I'm hoping you guys are willing to help me out.

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#### DerStrom8

##### Super Moderator
Most Helpful Member
Looking good! Keep us posted - always happy to help.

#### Usernametaken

##### New Member
So here are the specs, so far. Anyone able to confirm that this is all relatively OK?
Secondary winding height is 400mm on a 90mm dia. former wound with 36AWG wire. With the topload should give ~110Khz frequency.
MMC is 3 strings of 3 942C20P14K-F giving 6KV @ .15uF.
The bridge is yet to be decided on but probably a CM200DU-24F brick or a full bridge of TO-247s
Loneoceans UD2.7C driver.
Diy 555 interrupter for testing but will probably use a Onetesla interrupter in the finished coil.
Secondary will be using 1/4 inch copper pipe.

I run off 240V here.
Not looking for a ridiculously high powered coil, more a solid, reliable conversation piece to put in the loungeroom for people to look at.

Tested the UD2.7 tonight and it all appears to be working well. Now to wind up some GDTs.

#### DerStrom8

##### Super Moderator
Most Helpful Member
Will this be a DRSSTC or just an ISSTC?

DRSSTC.

#### DerStrom8

##### Super Moderator
Most Helpful Member
In that case I'm afraid 6kV won't be enough for the tank cap. You should rate your capacitor for about 30x the DC bus voltage. In your case if you're running it off 240V mains, this rectifies to 339.4V. Multiply by 30 to get 10.18kV. This is the minimum voltage I'd recommend rating your capacitor bank for. Also, from personal experience, 150nF may work but you'll get better results from closer to 250nF, for a coil your size.

#### Usernametaken

##### New Member
Oh.
That's going to add up to a lot of caps...

#### atferrari

##### Well-Known Member
Not looking for a ridiculously high powered coil, more a solid, reliable conversation piece to put in the loungeroom for people to look at.
Protected like the Gioconda, I hope.

#### DerStrom8

##### Super Moderator
Most Helpful Member
Oh.
That's going to add up to a lot of caps...
I'm afraid so. Capacitor banks often add up to being one of the most expensive parts of a DRSSTC. My coil uses 36 Aerovox RBPS IGBT snubber capacitors (2uF 530VAC each, 18s x 2p) giving me 222nF at 9.54kV. I'm running off 120V mains (170VDC bus) so this was plenty for me. You could probably get away with a similar setup but you'll risk blowing caps. I bought 50 of these capacitors from an online surplus store for $55 including shipping. #### Usernametaken ##### New Member #### DerStrom8 ##### Super Moderator Most Helpful Member Ouch,$20 a pop? Keep in mind the AC rating is probably about half the DC rating, so you'd need at least 17 of them in series to get the voltage rating you need. Even with the high price of caps for DRSSTCs you shouldn't have to spend $340+. See if you can find someone selling these Aerovox RBPS 2uF 1000VDC (530VAC) caps in bulk: https://www.ebay.com/itm/Aerovox-RBPS-IGBT-Snubber-Capacitors-2-0UF-1000VDC/352069951944?hash=item51f90121c8:g:yuYAAOSwvjdZOZdU They're tried and true. I haven't had a single problem with mine. Last edited: #### Usernametaken ##### New Member That’s$20 for 4 though so it isn’t that bad.
I’ll look into those aerovox ones tomorrow though.
Thank you.

#### DerStrom8

##### Super Moderator
Most Helpful Member
That’s \$20 for 4 though so it isn’t that bad.
I’ll look into those aerovox ones tomorrow though.
Thank you.
Woops, misread that, you're right.

#### Usernametaken

##### New Member
My calculations for the tank cap size were done through JavaTC, I take it this is incorrect?

#### DerStrom8

##### Super Moderator
Most Helpful Member
My calculations for the tank cap size were done through JavaTC, I take it this is incorrect?
Which tool did you use? Generally you need to select your capacitor bank and then tailor your primary coil to match. You'll need to find a balance between the two.
I don't see any information about the capacitor itself. If you can find a datasheet I'd be happy to look it over.

#### DerStrom8

##### Super Moderator
Most Helpful Member
I actually found the datasheet right after I asked

Looks like they are rated for 4000VDC/1600VAC. You might be able to get by with a string of 5 of these in series (with proper bleeder/balancing resistors), giving you a peak voltage rating of #caps * Vrated(AC) * sqrt(2) = 5 * 1600 * sqrt(2) = 11,314V peak and a capacitance of 1uF/5 = 200nF.

Based on this value your primary would need to have an inductance of around 10.5uH. This seems a bit low but it'll get you started. You could always add a sixth capacitor in the string, bringing the total capacitance to 167nF, which would require a primary coil inductance of 12.6uH. This might actually be an even better start.

#### Usernametaken

##### New Member
Thanks for all the help
JavaTC suggests a primary inductance of 13.953uH so I'll look at 6 of them.

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