Re: Large DRSSTC plan
Steve Ward, Mon Sept 24 2007, 12:54AM

You dont need a full bridge for your coil, that single half-bridge is far more powerful than you might think. While i do have those IGBTs (2 of them), i cant say that i'm willing to give them up, they are just too cool.

Re: Large DRSSTC plan
Danielle, Mon Sept 24 2007, 01:14AM

oh I know how nice that is, I just would much rather use a H-bridge... I am building a huge PSU that I can use for any tesla coil (under 60Khz) and as a base for pretty much any high power use I want, induction heating ect. I am trying to get it past 20KW system... this is my project for the next 2 years. I also purchased a 106A 1200V doubler diode module so that will power the DC bus and the 900V 2400uf capacitance should be enough. I plan to switch 800VDC... or should 240VAC doubled 678VDC at probably max of 60A on my homes special 240VAC 200A line (we had it specially installed separate from the homes line)

Re: Large DRSSTC plan
Steve Ward, Mon Sept 24 2007, 03:20AM

That sounds like a pretty decent idea. I think your filter cap should be far larger if you ever want to get more than 1-2kW out. Im using 6000uF at 700VDC on my coil which gets up to around 8kW. Typically, to handle the ripple current you will need rather large capacitors, probably up to 10,000uF across your supply.

Re: Large DRSSTC plan
Danielle, Mon Sept 24 2007, 07:15AM

so you really would think I need a 6.6kJ cap bank for this, if so I may be able to get (24) 2400uf 450V capacitors for $60 that will give me 900V 14,400uf....That is rather large for a tank capacitor is it necessary or is that only can crusher stuff?

Re: Large DRSSTC plan
Steve Conner, Mon Sept 24 2007, 10:07AM

That single brick would give you something like 8-9 foot arcs in a DRSSTC. It should also easily handle 20kW of CW power, if you want to do induction heating experiments and the like. With a 600V DC bus, you can get nearly 10kW CW from a bunch of TO-247s anyway.

If you want to make a DRSSTC with 20kW average power, well, that is another story, as it implies a peak pulse power of several megawatts If I were doing that, I think I'd want a H-bridge of the next IGBT size up (the CM600 type) at least, maybe even two H-bridges with their outputs combined in some way, and I'd be looking for sparks around 16-20ft long from a 7ft x 18" secondary tuned to 25kHz. So I wouldn't start constructing such a thing unless I knew I had access to a 40ft x 40ft workshop with a 27ft high ceiling

This thread should perhaps be moved to another board if you want to discuss the design of your proposed system.

FWIW, I'd sell you one if I had one but I don't :(

Re: Large DRSSTC plan
Danielle, Mon Sept 24 2007, 04:01PM

I see what the litmitations are and I still would rather use a H-Brige of CM400s this will be pleanty for what I will do. I do plan to only use 12 of the 2400uf 450V caps and rate the supply for 20KW. I do not think I am ready to spend the money on 4 CM600s and I think 9ft arcs are large enough for me. I just would like this thred here untill I find someone who would sell me one of them!

thanks everyone for the help.

Daniel Costantino.

Re: Large DRSSTC plan
Dago, Mon Sept 24 2007, 06:06PM

I'd say you need quite a few more bricks than two if you're inexperienced with DRSSTCs/SSTCs because you will most certainly kill a few. They die very easily when stressed over the maximum ratings in DRSSTC duty.

Re: Large DRSSTC plan
Steve Ward, Mon Sept 24 2007, 11:17PM

Yep, even with all the safety features you can think of, they dont mean a thing unless they are implemented properly and are proven to work. This stuff is very sensitive and id say its pretty hard to get it all right the first time around especially being somewhat new to electronics... and given your age you are new.

Im not trying to discredit you in any way, but its pretty foolish to base a whole design on a part that you have trouble finding more than 1 of. Ive only seen a few of these IGBTs on ebay in the past... on the other hand, CM300s and CM600s are very common, and can often be had for about 20 bucks each.

Also, wanting 20kW at a high-ish frequency is what i would consider wanting too much. Either design something for power at low frequency (where you would actually use that much power), or go for less power and more frequency. Its just a trade off you have to make, unless you have the money to buy the best parts on the market (and even still, a 20kW DRSSTC at 60khz is pretty unrealistic).

Re: Large DRSSTC plan
Danielle, Tue Sept 25 2007, 12:52AM

I understand I plan to get this working with a half and H-bridge of CM300s and then put this in after I have it running consistently without faliuars. I did understand though I was asking for alot and first plan to have my Drive scurcite witch contain everything but the IGBTs and caps.

I think that a more realistic plan will be for a 10-60Khz 10KW system.

Thanks Steve for the hint on ebay I got my first one for $30 so it wasnt too bad for something much faster and powerful than the CM400.

Re: Large DRSSTC plan
Danielle, Wed Sept 26 2007, 03:43AM

I am ok with a mod moving this to the form that you think most appropriate.

I have a question about the voltage divider on the half bridge, I know to use good film caps I was planning to use when put together 10 caps 5 on each side, 1000V 5uf will that be enough for the power levels I am talking about?

Re: Large DRSSTC plan
Steve Conner, Wed Sept 26 2007, 10:16AM

You need to use two banks of electrolytics in series anyway, to handle your 600V bus. So just use those as the "voltage divider" too.

BTW, if you drill your heatsinks with a few different sets of holes, you can probably get most half-bridge bricks to fit. Mine will take either Semikron or Powerex F-series.

Re: Large DRSSTC plan
Danielle, Thu Sept 27 2007, 01:08AM

thanks for the design tips I will need to figure out what to do with the 12 2400uf 450V caps that arrived today my parents were really upset lol that was a great deal though $29! I will need to figure out the best lay out for alot of them with low inductance bus bars connecting to the IGBT directly.

The only reason I questioned the divider because in a smaller coil the caps blew up after a long operation. I wasnt able to figure out if it was the caps were just too small, but if you think I can build it with the main caps as the divider I will.

I plan to though build it so I can without permanent changes move from a H-brige to half bridge.

and one last question is that can I use a simple comparator and resistor as a soft start? so when it is powered on the cap bank wont bring down the house, all it is that the power would be switched by a relay on startup through a 100ohm power resistor untill it reaches full charge then will trigger the relay to switch to a direct connection. or for a nice PSU like this should I build something like a powerful IGBT dimmer, I think that would be unnecessary though because I have full control by the inturupter?

Thanks for the help and I will be posting some sketches on the designe or pics once I get started.

Re: Large DRSSTC plan
Finn Hammer, Thu Sept 27 2007, 06:06AM


You can buy a timer that switches a second relay to short out the resistor.
That`s how I did in the CCPS.
Then you can have slowblow fusing in the surge phase, and shift to fast blow fuses in the "run" phase.

Cheers, Finn Hammer

Re: Large DRSSTC plan
Danielle, Tue Oct 02 2007, 11:56PM

ok so here is what I have now I have the 12 2400uf 450V caps and doubler 106A 1.2KV, and the 400A 1200V CM400 IGBT I should be able to get on to construction as soon as my second CM400 and heat sink arrive.

I am also working on the control circuitry along with this. now to just decide how many caps to use. All of them, sounds good.





one thing is that I am getting a 300A very similar model IGBT and the CM400 these are faster (60Khz) than the slandered CM. the ratings are verry similar and I wont go to 300A do you think I can use 2 different modules?