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Is this a suitable thyristor for induction launcher?

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LAN_403

Quantum Singularity

Thu May 25 2006, 12:49AM

Registered Member #158 Joined: Sun Feb 12 2006, 09:53PM
Location: Central Ohio
Posts: 282

Yes... I have another SCR question. Because I am uncertain about my stud mount scr's holding up to a fairly high power induction launcher, I am thinking I might just use those for a reluctance coilgun were I will be dealing with multiple lower powered stages. So I am looking for a more robust scr for a multi-kJ single shot induction launcher. I have seen one and I thought I would post some of its specs here to see if anyone thinks it would work. It is extremely robust for I ratings but due to its original application I am not sure if it is 'fast enough'. Here goes:

MARCONI AUTOMOTIVE STYLE SCR CONTACTOR FROM WORKING PRESS WELDER

WELDING RATING AMPS RMS AT 100% DUTY CYCLE ------1200

SGL. CYCLE SURGE CURRENT ( ITSM ) ----------------------------10000

SCR VOLTAGE RATING ( PIV ) (VRRM )-----------------------------2600

THIS UNIT IS DIRECT WATER COOLED

The unit is complete with a housing with what appears to be 2 large puck scr's. It has large buss bars for connecting. The current rating alone tells me that it should take anything I can throw at it, under 2600V anyways. This unit is a little pricey but well worth it I beleive if it will work well for a few kJ induction launcher. Any opinions are appreciated.

Self Defenestrate

Thu May 25 2006, 03:20AM

Registered Member #87 Joined: Thu Feb 09 2006, 01:36PM
Location: San Jose
Posts: 191

Sounds fine to me. Hit the gate hard, and check any insulation on the clamp. Nothing worse than an unexpected discharge.

Plasmaniac

Thu May 25 2006, 10:03AM

Registered Member #206 Joined: Sat Feb 18 2006, 03:17PM
Location:
Posts: 72

My first induction coilun desing blew a 1,1kV 10kA surge SRC at something around 1kV and 40ÂµF because the kickback diode was killed the shot before, so make sure you use a suitable one.

Quantum Singularity

Thu May 25 2006, 01:59PM

Registered Member #158 Joined: Sun Feb 12 2006, 09:53PM
Location: Central Ohio
Posts: 282

Wow, it seems like it would take a lot to blow an 10kA rated scr.... epsecially with only 20 joules. Is that right...just 40uF and 1kV? Anyhow, I will definately use large diodes. The current ones I have are rated 85A continuous and 800V I beleive. Cant remember the surge rating but I beleive it was atleast 1kA. I have 6 of them and would probably parallel all of them for a couple kJ bank. But I am still looking for larger ones if I happen to find a good deal. The ones I have a 'standard recovery' power diodes (stud mount). I was concerned because I noticed some folks here have used high power ultra-fast type diodes. But the 'ultra-fast' is a rating of the turn off time right? For clamping we are primarily concerned with turn on time so the diode can provide a short across the coil to keep the voltage from rising very high. And the conduction time even in a standerd recovery rectifier is much quicker that its turn off time - correct?

Electroholic

Thu May 25 2006, 03:52PM

Registered Member #191 Joined: Fri Feb 17 2006, 02:01AM
Location: Esbjerg Denmark
Posts: 720

Yes. you are correct.
standard diodes are fine.

Plasmaniac

Thu May 25 2006, 06:47PM

Registered Member #206 Joined: Sat Feb 18 2006, 03:17PM
Location:
Posts: 72

I used 1n5408s (I know this was stupid). It seems like the kickback current exceeded 200A and blew the diodes, so I had nearly no load when I triggered the puk the second time. I also never thought that <20J can blow a puk...

Self Defenestrate

Thu May 25 2006, 10:00PM

Registered Member #87 Joined: Thu Feb 09 2006, 01:36PM
Location: San Jose
Posts: 191

For protection diodes, I use a semikron bridge rectifier, rectifier modules tend to have some good surge ratings. Something to keep an eye out for.

Eric

Thu May 25 2006, 10:46PM

Registered Member #69 Joined: Thu Feb 09 2006, 07:42AM
Location:
Posts: 116

If you are not going to be using electrolytic caps you ought not to need a protection diode. Seems like these are often a major point of failure since they typically have a lower peak current handling ability than the SCR. You can always protect the SCR with a snubber and perhaps a TVS to absorb any turn-off transient.

As far as the SCR goes, sounds like a winner in terms of current handling ability. If ITSM is 10KA then you can probably do more than twice that for short duration pulses (~1ms). One thing to look at is the turn on time, max dI/dt, etc. to see how it will switch the kind of fast pulse you'd be generating. If you exceed that, it could fail. Got a datasheet?

Quantum Singularity

Fri May 26 2006, 12:09AM

Registered Member #158 Joined: Sun Feb 12 2006, 09:53PM
Location: Central Ohio
Posts: 282

Eric - I will be using the SCR's for electrolytic banks. I dont think it would be feasable for me to try solid state switching on my maxwells.

Thanks everyone for the opinions. Unfortunately I am shying away from that particular SCR module. I have found some smaller and cheaper ones rated nearly as high. And no, there was no datasheet provided nor part #'s so other than the given info the rest might be a mystery. If anyone is interested its on ebay at http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&rd=1&item=7622706878&ssPageName=STRK:MEWA:IT
The opening bid is $50 US. But the thing just looks like a monster, check it out. I will probably not bid so its open game.

The other ones I am currently looking at are Eupec modules for $10 each on ebay (please dont bid against me though please

). I am waiting on the guy to get back with me though, he is supposed to have 3 available. And there are very detailed specsheet on Mousers site here

But the important specs are:
1200V
6700A Itsm
200A/us dit/dt
500V/us critical rise time for off-state voltage
250mA max Igt
2.2V max Vgt

at 6700amps peak and with 3 units in parallel this may be more robust than the monster above, plus smaller and cheaper. This is a brick(?) style unit. And again, for these I have vary detailed specsheet available.

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