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ZakWolf

Fri Mar 11 2011, 03:29AM

Registered Member #3114 Joined: Sat Aug 14 2010, 08:33AM
Location:
Posts: 608

Sorry for this over asked question but I really donâ€™t want to mess this up, I am building my new 356 joule coil gun and have been testing it. I am using two nails for a switch which is not very efficient, very dangerous and defiantly not portable (which is what I plan on). I found this SCR on mouser

will this with stand a 450v 3600uf capacitor bank?.Also I have read that I need a diode to protect the caps from reverse voltage, but I also heard that this causes suck back to happen. Could you please help me find the Diode and SCR rating I need. Thank you

here is a video of the coilgun in action

Turkey9

Fri Mar 11 2011, 04:33AM

Registered Member #1451 Joined: Wed Apr 23 2008, 03:48AM
Location: Boulder, Co
Posts: 661

I don't think a single one of those SCRs would hold up. You really need to simulate your coil using Barry's sims and find the estimated peak current.

The reverse diode is really to protect everything. The back emf will blow your scr before the caps get damaged. Put it in parallel with your coil with orientation so that the current during discharge won't flow through it. It won't cause suckback at all. It simply absorbs all the left over energy that wasn't put into the projectile.

ZakWolf

Fri Mar 11 2011, 05:22AM

Registered Member #3114 Joined: Sat Aug 14 2010, 08:33AM
Location:
Posts: 608

would mouser carry an SCR capable of handling that amount of power. what would i be looking for?

Turkey9

Fri Mar 11 2011, 06:51AM

Registered Member #1451 Joined: Wed Apr 23 2008, 03:48AM
Location: Boulder, Co
Posts: 661

You can hook them in parallel for added current handling capabilities. Add the surge currents of each and down rate by 80%.

ZakWolf

Fri Mar 11 2011, 05:02PM

Registered Member #3114 Joined: Sat Aug 14 2010, 08:33AM
Location:
Posts: 608

I was looking at higher rated SCR's would this work or do i need to put them in parallel

. If i put them in parallel i just face them in the same direction so that the Gate, Anode, Cathode are together correct? Could i also turn on the SCR with 3v or would that kill it?

Saz43

Fri Mar 11 2011, 07:50PM

Registered Member #1525 Joined: Mon Jun 09 2008, 12:16AM
Location: America
Posts: 294

It all depends. Here's what you have to do in order to answer your questions:

1. Go here

and simulate your coil. This is easy to do if you have a ruler.

2. Ho here

and simulate your RLC circuit. Also easy to do provided you have completed step 1.

3. Check the data sheet for your SCR to see if it can handle the peak current estimated in step 2. Take the average forward current rating of the SCR and multiply by 10 for an estimate of peak current handeling.

4. Will 3V fry your SCR? Check the data sheet for V_gate and I_gate to know how to trigger your SCR.

I'd also reccomend eBay for SCRs. I got the monster SCR (800V, 3500A) for my coilgun for only $25.
Nice coilgun by the way. It seems to be working very well for a preliminary design. Keep it up!

ZakWolf

Sat Mar 12 2011, 12:40AM

Registered Member #3114 Joined: Sat Aug 14 2010, 08:33AM
Location:
Posts: 608

thanks for checking it out. i will look over the scr data sheet and try out those simulators

Inducktion

Wed Mar 16 2011, 08:07PM

Registered Member #3637 Joined: Fri Jan 21 2011, 11:07PM
Location: Buffalo, NY
Posts: 1068

Just a quick question, when putting SCR's in parallel, generally what needs to be done? And also, I believe I have two types of SCR's, ones 1200 volts and the other is 600 volts, but they can both handle 610 amps of peak current. Would it be unwise to parallel them due to their voltage differences, or will they be fine? They're the same series so I don't believe it would be an issue. h

Here's a link to their datasheets.

thanks

Shrad

Wed Mar 16 2011, 08:19PM

Registered Member #3215 Joined: Sun Sept 19 2010, 08:42PM
Location:
Posts: 780

if anyone is interested, I have BIG thyristors varying from 400A pulse to 1000A pulse, brick models with dual series thyristor

EDIT:

confirmed for 6 AEG 1200V 200Amps (3600 amps max pulse discharge), if you're interested please tell me so we can work something (I need wire... mucho wire...)

James

Mon Apr 11 2011, 09:16PM

Registered Member #3610 Joined: Thu Jan 13 2011, 03:29AM
Location: Seattle, WA
Posts: 506

The sort of SCR you're looking for are the big stud mount things of the sort used in early generation industrial motor controls, electric forklifts and diesel electric locomotives.

In my capacitive discharge spot welder I used a 100A 1200V SCR because it's what I found for a good deal on ebay. I've measured the peak discharge current out of the 1F capacitor bank at just under 10kA and the SCR has held up so far.

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