# Finally starting on my coil...

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#### DerStrom8

##### Super Moderator
Thanks for all the help
JavaTC suggests a primary inductance of 13.953uH so I'll look at 6 of them.
Keep in mind the 13.953uH will change based on capacitor tolerance, leadout length, etc. This is the value that is "tuned" when you tune a Tesla coil. JavaTC has an "Auto-tune" tool, and this is exactly what it adjusts.

##### New Member
A couple of quick questions whilst I finalise my JavaTC simulation:
How far from the secondary coil do I want the first turn of the primary and what do I do in relation to coupling (I take it this is how far above/below the plane of the primary that the first wind of the secondary is placed)?

#### DerStrom8

##### Super Moderator
A couple of quick questions whilst I finalise my JavaTC simulation:
How far from the secondary coil do I want the first turn of the primary and what do I do in relation to coupling (I take it this is how far above/below the plane of the primary that the first wind of the secondary is placed)?
1. For a coil the size of yours I would recommend at least half an inch between the first turn of the secondary and the innermost turn of the primary coil
2. The coupling coefficient is directly related to the positioning of the secondary coil within the primary. Generally you should shoot for between 0.1 and 0.2. 0.13 is usually recommended as the target. JavaTC also has a tool to automatically adjust the coupling too, along with auto-tune. I recommend using it.

##### New 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.
Found these as well.
https://www.aliexpress.com/item/Tes...656576e&transAbTest=ae803_1&priceBeautifyAB=0

#### DerStrom8

##### Super Moderator
Those caps look fairly nice, though the seller clearly doesn't know what they're talking about or how caps are rated.

The one downside is that the AC rating of those caps is not listed. We'd have to check the datasheet for that in order to determine how many are needed.

Shipping to Australia will definitely be the tricky part.

#### DerStrom8

##### Super Moderator
Excellent! I'd go for four in series to give you a 12000VAC rating. That will give you a capacitance of only 110nF though, so if you have the money to spare you might consider putting two of these strings in parallel (8 caps total, ~\$160). Heck, I'm even tempted, though they don't ship to the US. That's actually a pretty decent deal for that type of capacitor. I do see the ESR is around 2 ohms. That seems a little high, so keep an eye on their temperature. They'll be dissipating a lot of power.

##### New Member
The ones I linked to are actually 6000VDC.
I've ordered 2 of them for 12000VDC and 0.22uF which would be ideal.
Be interesting to see if/how they work and if they stand up to the coil.
Happy to get them delivered here and then forward them on to you if they don't ship to the US.

#### DerStrom8

##### Super Moderator
The ones I linked to are actually 6000VDC.
I've ordered 2 of them for 12000VDC and 0.22uF which would be ideal.
Be interesting to see if/how they work and if they stand up to the coil.
Happy to get them delivered here and then forward them on to you if they don't ship to the US.
Look at the datasheet. 6000VDC, 3000VAC each. You need to go by the AC rating when using them in Tesla coils. The AC rating is generally around half of the DC rating.

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