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Registered Member #15
Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068
Tom540 wrote ...
yeah thats why i said it was too thick. I mean itll work but itll work much better with thinner wire. My first SSTC ran at 1MHz and I think it used 22 awg wire.
And why would it work "Much Better" with thinner wire?
Registered Member #1517
Joined: Wed Jun 04 2008, 06:55AM
Location: Chico CA
Posts: 304
so let me get this straight.
I want more more turns mainly because of the step up right? And perhaps because of the feedback frequency range, needs to be within operating tolerance of the circuit yes?
Dr. K, so this is a medium size sstc? I thought it was a "mini" :P
either way I am unwinding the secondary and rewinding with 30 awg
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
coillah wrote ...
so let me get this straight.
I want more more turns mainly because of the step up right? And perhaps because of the feedback frequency range, needs to be within operating tolerance of the circuit yes?
Dr. K, so this is a medium size sstc? I thought it was a "mini" :P
I don't know, but my SSTC secondary has 3.5" diameter and 10" winding length and I call it medium I have never seen the monster coils use SSTC drive scheme, so for me medium SGTC=large SSTC.
You want more turns for lower switching frequency and more Vout. However as i said, too much turns can result in the secondary coil melting down, especially with non-interupted operation.
Registered Member #289
Joined: Mon Mar 06 2006, 10:45AM
Location: Conroe, TX
Posts: 154
Guys, there is one really good reason to wind a low frequency secondary that is being over looked here: switching loss.
The higher your resonant frequency the higher your total system losses. You will lose more power in your gate driver and more power in you bridge. That means hot parts that are more likely to fail. IMO you should aim for an operating frequency of less than 200khz. As Dan said, you can go as high as you want, but if this is your first coil a 14Mhz class E system is probably not a good idea
So, use the 30awg and wind it to 16" instead of 10".
Registered Member #989
Joined: Sat Sept 08 2007, 02:15AM
Location: São Paulo, Brazil
Posts: 476
Yeah, with higher frequency the cross-conduction gets worsed. But the biggest problem is on the driver, here all time that I need to run more than 800khz at the driver, I get much heat (some times I blow the drivers), that can be resolved with a IRF540/9540 bridge for the gdt driver with no problems, but you will get a more complicated gate driver. With something about 300Khz or so, you can use cheap TC442X or UCC's drivers for driving the GDT directly, and even running at CW, you will get only a little heat at drivers.
My secondary coil is 30cm height, and 4'' diameter, its near than 3:1 h:d and its working very fine, I was able to get 25cm sparks to air with an halfbridge of IRFP250 running at Halfwave retified mains.
Registered Member #15
Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068
hvguy wrote ...
Guys, there is one really good reason to wind a low frequency secondary that is being over looked here: switching loss.
The higher your resonant frequency the higher your total system losses. You will lose more power in your gate driver and more power in you bridge. That means hot parts that are more likely to fail. IMO you should aim for an operating frequency of less than 200khz. As Dan said, you can go as high as you want, but if this is your first coil a 14Mhz class E system is probably not a good idea
So, use the 30awg and wind it to 16" instead of 10".
We're not talking about switching frequency. The question asked is regarding wire size. I can make a 50kHz coil using both 30AWG and 20AWG and likewise make a similar one at 8MHz using 30AWG and 20AWG as well.
Someone made a comment that thicker is worst than thinner, and i'm asking that person to validate their claim.
Registered Member #289
Joined: Mon Mar 06 2006, 10:45AM
Location: Conroe, TX
Posts: 154
Since we are talking about wire size for a specific scenario, in this case Steve's mini SSTC, coillah would need to use smaller wire to achieve ideal results. Steve used 30ga for an Fres of about 225KHz. I would use at least that. 24ga yields an Fres of ~685KHz, this is far to high to realistically switch with IRFP260s in the arrangement shown. The losses would be very high at that frequency, especially in a CW system like this.
So Dan, I understand your point, and I agree. Wire size is irrelevant, it is the frequency (coil geometry) that matters and even that is topology dependent.
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24 AWG for Mini SSTC
I have never seen the monster coils use SSTC drive scheme, so for me medium SGTC=large SSTC.
