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Secondary self-resonance (with topload) should be around 110kHz.
Primary resonant capacitor:
MMC of GE42L series capacitors 100nF 3KV (7 strings of 3) for a total of 236nF (measured) at 9kV.
Primary coil
Diameter: 30 cm Number of turns: 6.5 1cm copper pipe Tuned to have a primary resonance around 95-100kHz (and then adjusted)
Coupling will be adjusted in order to have the best performances (spark length vs power in), I will start with 0.18 (estimated with JavaTC)
Bridge:
Full bridge of IXYS IXGN60N60C2D1. According to simulations, maximum primary current will be around 700A, I hope these components will handle the current…
Power supply:
Rectified mains (230Vac) filtered with two big 2200uF 450V electrolytic capacitors.
Controller:
Basically quite similar to “Steven Ward DRSST controller 1.3â€. The main difference is that I have added a R-C network right after the current transformer which anticipates the signal of some hundreds of ns in order to compensate driver+IGBT delay.
Interrupter:
Simply based on the classical 555, Ton variable between 0 and 400us, BPS from 50 to 300.
So far all the electronic parts have (almost) been completed, primary is finished while secondary and topload have still to be finished. See attached pictures.
Any comments/suggestions are welcome!
I will keep you updated.
Regards,
Luca
Secondary pipe with wire bobbin:
Primary coil:
The two big bulk capacitors:
MMC (I did not find enough GE caps, so the last string is made of CDE940C caps... )
IGBTs on the heatsink:
The FB completed. The two big cylinder are bypass capacitors (MKP 40uF 450V)
Detail of the GDT board mounted directly on the IGBT terminals:
Registered Member #2628
Joined: Fri Jan 15 2010, 12:23AM
Location:
Posts: 627
Very nice worksmanship, and best of luck with your coil! I do have one question though, is your bridge's heatsink made of 4 different ones? or is it 1 heatsink?
Registered Member #2481
Joined: Mon Nov 23 2009, 03:07PM
Location: ITALY
Posts: 134
Gatedbreakdown wrote ...
Very nice worksmanship, and best of luck with your coil! I do have one question though, is your bridge's heatsink made of 4 different ones? or is it 1 heatsink?
Thanks!
They are 2 heatsinks joined with the metallic bars visible in the pictures.
Registered Member #2292
Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795
Ok you have a lot of things wrong with your bridge, a lot
1. Don't use brass for you buss use copper 2. Your IGBTs are way to far apart i.e. there will be a lot of stray inductance that will case voltage spikes and blow up your IGBTs. Keep IGBTs as close as possible to minimizes stray inductance. 3. don't use laminated copper clad board use solid copper sheet. 4. you don't need 2 GDT cores 1 core is plenty (assuming it is ferrite) if it isn't a ferrite core you need to switch it out for one or your gate drive will not work properly. 5.those IGBTs can't handle 700A no way, don't run them higher than 500A 6.Get buss caps as close to the bridge as possible 7.And last but not least get some snubber caps on that bridge like 3uF or so.
Also you don't need the RC network on the controller you added, you only need to switch the devices early if they are really big slow IGBTs. The IGBTs you are using will run happily all the way up to 300KHz
Registered Member #195
Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111
I disagree with Goodchild on everything but current rating of your FET's. I have seen pictures done with clad board made with a drumel tool that came out fine. Minibrute uses a PCB. Just add a cuple of polypropalene caps in parallel with your electolytics as close as pausible to the FET's
Registered Member #2292
Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795
Everything you say?
I'm not saying it won't work, I'm just giving advice on how to make it better.
Copper clad works but solid copper sheet has less stray inductance witch in turn lowers voltage spices making it easier on the IGBTs.
Ive built DRSSTCs both ways and Ive made all the mistakes (well maybe not all but most) and the things I listed are from things that Ive learned over time.
btw they are IGBTs not FETs, MOSFETs are not suited for DRSSTC system because of there on resistance witch increases loses as the power level goes up.
Registered Member #2481
Joined: Mon Nov 23 2009, 03:07PM
Location: ITALY
Posts: 134
Goodchild wrote ...
Ok you have a lot of things wrong with your bridge, a lot
1. Don't use brass for you buss use copper 2. Your IGBTs are way to far apart i.e. there will be a lot of stray inductance that will case voltage spikes and blow up your IGBTs. Keep IGBTs as close as possible to minimizes stray inductance. 3. don't use laminated copper clad board use solid copper sheet. 4. you don't need 2 GDT cores 1 core is plenty (assuming it is ferrite) if it isn't a ferrite core you need to switch it out for one or your gate drive will not work properly. 5.those IGBTs can't handle 700A no way, don't run them higher than 500A 6.Get buss caps as close to the bridge as possible 7.And last but not least get some snubber caps on that bridge like 3uF or so.
Also you don't need the RC network on the controller you added, you only need to switch the devices early if they are really big slow IGBTs. The IGBTs you are using will run happily all the way up to 300KHz
Hi Goodchild
Some comments on your remarks:
1- Brass? It's copper, not brass... I used brass just to connect all the capacitors in parallel. Calculated resistance (with skin effect) is something like few mOhms...
2- Distances are in the order of some cm, traces are 2-3 cm wide, I do not think stray inductance will be that bad. Also, there are 1.5kW TVS right on the C-E terminals.
3- Why? Again, we are talking of mOhms of resistance. I have seen a lot of DRSSTC based on two-sides laminated copper clad.
4- Two is better than one . Obviously cores are made of ferrite. I have tested it (with the scope), it works perfectly.
5- Let's see... I want to touch with my hand this assumption... In case, probably I will switch to fairchild 40N60...
6-7 The two big white cylinder are 40uF Polypropilene capacitor. They are connected directly on the bus at few cm from the IGBTs. On the other hand, electrolytic capacitors have internal impedance of some hundreds of mOhms at 100kHz, so, it's not so crucialto connect them right on the switching devices. The inernal impedance of such caps is much higher than than the impedance of few cm of heavy copper wire. The important thing is to put quite big bypass capacitor (MKP) right on the devices.
Registered Member #2292
Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795
Ok look Ive be building DRSSTCs for a while now and you don't get sparks like this: Unless you know what your doing
Take a look at one of my bridges for example:
I'm just trying to give you some knowledge that took me almost a year of R&D and a large box of blow up IGBTs and parts to learn
Just to go over what you already said: yes I say copper because when you have currents in the 100s of amps range you want as low inductance as possible this same thing has to do with spacing as well you have to get those IGBTs very close together. If you notice I don't use TVS on my bridge.
you can use the copper clad board it would work, but if you want it to work better use solid copper sheet.
It may only be mOhms of resistance but we are also dealing with 100's if not 1000's of amps flowing in the circuit. Resistance is important to but even more important is the inductance.
If you find 40N60s let me know 40N60 are hard to come buy these days and if you do find them they will most likely be very expensive.
As long as your GDTs are ferrite they should work fine I'm as just saying if you want to free up some space use 1.
A 40uF snubber won't do much you need to use smaller values like < 5uF. They should also be film caps if you can get them.
Registered Member #195
Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111
Hi Goodchild, your DRSSTC is very nice and your construction techniques are well done you just come off as a critic. A failing I have had on occasion. Some of the earliest bridges are done with pcb including minibrute. For this application the losses in brass or copper or aluminum will be negligible because resistance is in the milliohms. your semiconductors and primary have the greatest amount of resistance in them. If we were passing amps for more than a few microseconds it may be an issue. your statmens about parasitics I agree with but I have seen pictures of DRSSTC's that were geroge jobs with wires that worked. The biggest strives made are in the controle electronics for the gates and I think that Luca needs to pay attension to the circuit that he uses.
Luca some of the older circuits that were created sometimes eat fet ,and some work, and some do beter with people with an under standing of electronics and tesla resonance theory. I have tried Steve Wards newest publised circuit that seems to work well.
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My first DRSSTC - Video added
. Obviously cores are made of ferrite. I have tested it (with the scope), it works perfectly.
40N60 are hard to come buy these days and if you do find them they will most likely be very expensive.
My controller is similer (in principle) to Steve Ward driver...