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Registered Member #139
Joined: Sat Feb 11 2006, 11:01AM
Location: Perth, Western Australia
Posts: 358
Right, the time has come to make my first DRSSTC and I have a few questions. I was going to go for a rather large (250x1000mm secondary) but have decided that due to the fact that my IGBT's are only rated for 600V/120A (FGA40N60) I will go for a slightly smaller secondary. I'll probably use steve c's PLL driver, as I like the idea of being able to use it as an SSTC as well. Now a few Q's
1. Is a 1 metre long primary feasable with the semi's I have? (I would like to bite the bullet and build a decent sized coil first off) is 0.5mm wire too large/small for this size of coil?
2. How closely do I have to watch the amount of secondary turns? I want the Fres as low as possible. But obviusly don't want to overdo it with the turns. i.e. 0.25mm wire means I have a Fres low enough to try my bricks on, but I think 4000 odd turns is a bit excessive.
3. How do I calculate the size of the MMC and primary turns? Due to my lack of EE experience, a lot of my work is "eddisonian" i.e. try it until you find something that works. I would like to avoid this situation.
Registered Member #75
Joined: Thu Feb 09 2006, 09:30AM
Location: Montana, USA
Posts: 711
1. You can always run the big coil at low power and get some bigger IGBTs later, so why not. 2. Modern IGBTs can easily switch at 100s of kHz, so with a 1m secondary I don't think you will have too many problems with this. 2000 turns would probably be plenty. 3. You want to match the resonant frequencys of the primary and secondary circuits. If you know the secondary frequency (from for example), and you know the primary inductance (from the same link I suppose), you can use that to figure out the capacitance by f=1/(2 pi sqrt(LC)) or, heck, just let the program do it for you ...
Registered Member #146
Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055
Just wanted to address one of your questions more specifically:
3. How do I calculate the size of the MMC and primary turns? Due to my lack of EE experience, a lot of my work is "eddisonian" i.e. try it until you find something that works. I would like to avoid this situation.
This is a common question, since DRSSTCs dont have any real guidline for setting the capacitor size (unlike an NST coil where you know basically the largest cap you can charge in 8.33 or 10mS). What i find in general is that all of my DRSSTCs tend to use around 5-9 primary turns (its not too helpful to talk about "turns", i should be talking inductances, but this is very general and a pretty wide open topic). So my suggestion is to simply design a primary with say 8-10 turns, and then use a TC calculator to 1) determine its inductance, then 2) figure out how big to make the tank Cap to resonate at 25% lower frequency than that of the secondary (this gives you a good range to tuning options).
Also, all of my coils use MMCs of 75nF or larger... my larger coils use .45-.7uF or so. I generally like to use bigger capacitances as it allows for greater energy transfer in a shorter amount of time (a very good thing for DRSSTCs!).
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First DRSSTC
