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I need those heatsinks for my DRSSTC halfbridge and MMC, the SCRs are like a bonus. Only thing is I can't find a datasheet for them anywhere on the net. Anyone seen them before?
The cost? $54! Equivalent-rated ones usually cost almost double that, EACH, without the heatsink! Guess now I have to build a large coilgun at some point.
Registered Member #177
Joined: Wed Feb 15 2006, 02:16PM
Location: Munich, Germany
Posts: 214
I guess you already know that if you disassemble the stack, the SCR are pretty much useless. Without the axial pressure they will probably fail to fully conduct.
Registered Member #690
Joined: Tue May 08 2007, 03:47AM
Location: New Jersey, USA
Posts: 616
Oh yeah, like those ones I've seen on Digikey that are never in stock and cost like $800+? You could like blow up the ocean with one of those...
Not that I plan on trying this, but if you connect all the gates can you series-parallel SCRs? I think I've heard of people doing this on a small scale, not sure.
Registered Member #146
Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055
Not that I plan on trying this, but if you connect all the gates can you series-parallel SCRs? I think I've heard of people doing this on a small scale, not sure.
Series them? yes, doable. Parallel them? depending on what tricks are available, also doable.
BTW, those are just mini-pucks . Ive got lots of those sitting around, hehe. Not a bad deal on the heatsink, but i have bought similar SCRs for $3-4 each. Still never built a worth-while coilgun :P.
Registered Member #690
Joined: Tue May 08 2007, 03:47AM
Location: New Jersey, USA
Posts: 616
I will be mounting a half-bridge or possibly full-bridge of TO-227B case 40N60 IGBTs to the heatsink. You, Steve, actually told me in a previous thread to just keep an eye on Ebay for "slabs of heatsink". Well, I found one; the attached SCRs are sort of a bonus.
There are 3 sections of heatsink, two small ones (relatively) and a large base piece which is the one I'll be using on the IGBTs. I can still sandwich one SCR between the two smaller heatsinks to use for a coilgun or something.
As for them being useless without their clamps, I was wondering if I could sandwich them between two 1"dia by .5" NIB magnets, then just stick some large bolts to the magnets as screw terminals. Would this work?
Oh and it also came with 2 sections of MASSIVE triple-O gauge wire with attached terminals. Those will be great for the half-bridge bus.
Registered Member #146
Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055
I havent really messed with Nd magnets that much, but i dont think they would have the necessary clamping force. You can make your own clamp with some bits of aluminum and thick plastic to make insulators for the clamping bolts. Im not sure how you would know the clamping force, but i think there are washers out there that compress at a specific force?
Registered Member #56
Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445
To make my clamp I used a piece of Al heatsink (1/4" thick cast plate with 1/4" fins sticking out), with the outer fins sawed off, and a 1/2" bolt in each corner. For the cathode I just put a piece of copper foil under the SCR, and for the anode I used another piece of foil on top of a piece of 1/8" thick PVC. Then I torqued the bolts as tight as I could get them (only about 50ft-lbs since it was damn hard to hold onto the thing), which deformed the Al slightly. IIRC, it was a 400a SCR, and I accidentally discharged my bank (2x 450v 3300uF caps seriesed, inverter grade, all low R and L connections) through it into a shorted diode, and it didn't even flinch Although I will tell you I did when that diode exploded...
I seriously doubt that Nd magnets would do the trick, you need a ton (literally) of force on the SCR.
Registered Member #690
Joined: Tue May 08 2007, 03:47AM
Location: New Jersey, USA
Posts: 616
The bolts on the heatsinks that actually did the clamping all had a particularly thick "spring washer" between them, at least I think thats what they are called. Looks like a normal washer, but it is split and the ends are slightly offset each other. Is this what you were referring to, Steve?
I tightened the bolts on my single-SCR setup until these were totally compressed together, seems about the same tightness as when I disassembled it. I have tested it by discharging a single 2900uF 350V cap through it into the coil from my photoflash-powered coilgun. This was over 5 times the capacitance it was designed for, so the projectile shot out the backwards out of the coil with more force than it ever came out the front in its normal setup. Suckback can be good!
I was ready for something like this, so I had newspapers at both ends of the coil. It might have broken a window, otherwise.
I'd like to make a smaller clamp, though, as the current heatsinks are pretty massive.
Registered Member #546
Joined: Fri Feb 23 2007, 11:43PM
Location: Albuquerque, NM
Posts: 239
You know a torque wrench isn't too expensive, and would take a LOT of the guesswork out of things.
Also, make sure you use properly rated bolts for the tension they'll be under. The last thing you want is a ballistic bolt head flying across the room when the whole unit heats up and over-stresses a bolt.
The other option, of course, is to just entirely over engineer the thing with 3-4x the bolts needed.
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