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Forums
4hv.org :: Forums :: Electromagnetic Projectile Accelerators
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how to use an SCR?
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Solidacid
Tue May 12 2009, 09:51PM Print
Solidacid Registered Member #1430 Joined: Sun Apr 06 2008, 11:12AM
Location: Ã…rhus, Denmark
Posts: 102
 		today i recieved an SCR i bought on ebay, HERE

i having trouble using it though, it has 2 sides(obviously) and 2 wires a white and a red(the red one is connected straight to one of the plates).

what i HAVE tried:
  • ohmmeter with positive wire on the white SCR wire and negative on the red = 19 ohms

  • ohmmeter with negative wire on the red SCR wire and positive on the other plate = 0.320M ohms

  • ohmmeter with positive wire on red SCR wire and negative on the other plate = flashing ohmmeter?

  • ohmmeter with positive wire on the plate, negative on red/white both = 0.340 ohms


  • ohmmeter with positive wire on red SCR wire, negative wire on the other plate, 0v to red SCR wire and 3v to white SCR wire = 5.74M ohms


any ideas on how to use this thing?
i wanna use it for a coilgun.

Pics
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big5824
Tue May 12 2009, 10:22PM
big5824 Registered Member #1687 Joined: Tue Sept 09 2008, 08:47PM
Location: UK, Darlington
Posts: 240
 		The small plate is the anode, large plate with the red wire is cathode, and white wire is gate. Dont use the red wire, its too thin for high currents.

Also, these devices break easily, especially with too much voltage/current through the gate, so dont go sticking an ohmeter across everything :) some scrs have a max gate voltage of only 2v.

Oh and you need to clamp the SCR with a fair amount of force to ensure a good connection between the semiconducting layers, minimum force for that SCR is 3300N
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rp181
Wed May 13 2009, 02:17AM
rp181 Registered Member #1062 Joined: Tue Oct 16 2007, 02:01AM
Location:
Posts: 1529
 		the red wire is a aux cathode for the gate.
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Solidacid
Wed May 13 2009, 06:15AM
Solidacid Registered Member #1430 Joined: Sun Apr 06 2008, 11:12AM
Location: Ã…rhus, Denmark
Posts: 102
big5824 wrote ...

The small plate is the anode, large plate with the red wire is cathode, and white wire is gate. Dont use the red wire, its too thin for high currents.

Also, these devices break easily, especially with too much voltage/current through the gate, so dont go sticking an ohmeter across everything :) some scrs have a max gate voltage of only 2v.

Oh and you need to clamp the SCR with a fair amount of force to ensure a good connection between the semiconducting layers, minimum force for that SCR is 3300N

how would i go about measuring the pressure on the scr? im thinking about sandwiching it between 2 pieces of metal(heatsinks) and use some screws to hold them together
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big5824
Wed May 13 2009, 07:15AM
big5824 Registered Member #1687 Joined: Tue Sept 09 2008, 08:47PM
Location: UK, Darlington
Posts: 240
 		I havent applied the final required pressure to my SCRs yet, but i think i will use a torque wrench.....not quite sure how though.
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klugesmith
Wed May 13 2009, 08:54AM
klugesmith Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1715
 		For controlled clamping force you might look at Belleville washers (described at wikipedia; prices & datasheets at McMaster-Carr).
If you use bolts directly, they should be as long as possible and no thicker than necessary for strength. The bolt elongation forms a controlled "spring" so the clamping force is less sensitive to differential thermal expansion.

Rich
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Solidacid
Wed May 13 2009, 03:50PM
Solidacid Registered Member #1430 Joined: Sun Apr 06 2008, 11:12AM
Location: Ã…rhus, Denmark
Posts: 102
 		i haven't gotten it clamped yet, but i just tested it, it works :D
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