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quick SCR question

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EvilTesla-RG

Thu Jun 25 2009, 06:42PM

Registered Member #1523 Joined: Sat Jun 07 2008, 02:05PM
Location:
Posts: 97

I am trying to find a SCR for my first coil gun, and I seem to be having difficulty doing so.

Would anyone mind helping me out?

I will be using Photo flash capacitors, charged by a camera flash charging circuit.

thanks.

Bonehead

Thu Jun 25 2009, 06:53PM

Registered Member #2046 Joined: Sun Mar 22 2009, 01:12PM
Location: Stockholm, Sweden
Posts: 23

Difficulty finding a place to buy them or choosing one..?

EvilTesla-RG

Thu Jun 25 2009, 07:38PM

Registered Member #1523 Joined: Sat Jun 07 2008, 02:05PM
Location:
Posts: 97

Both.

Also, I'd like to not have to be constantly turning my charging circuit on and off all the time. So, is their a way to add in a transistor or something so that when I flip the switch to turn on the SCR, it turns off my charging circuit untill I release the switch?

Z28Fistergod

Thu Jun 25 2009, 07:50PM

Registered Member #2040 Joined: Fri Mar 20 2009, 10:13PM
Location: Fairfax VA
Posts: 180

Try ebay, but beware of counterfeit components. The simplest solution to turn your charging circuit off is to use a DPDT pushbutton.

EvilTesla-RG

Fri Jun 26 2009, 12:29AM

Registered Member #1523 Joined: Sat Jun 07 2008, 02:05PM
Location:
Posts: 97

I'll try Ebay some more.

I did try it earlier, but I didn't have much luck.

I decided to go with a logic inverter (NOT gate) to turn off the charging ciruit.

I know that is a little extra complication, but I go to college (second year) in two months. So this will be the last project I get to do. I want it to be nice.

Edit:

would this one work?

Data sheet

Electroholic

Fri Jun 26 2009, 03:55AM

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

It's kinda hard to tell without other specs.

Capacitor bank size/coil inductance/resistance etc.

Barry

Fri Jun 26 2009, 05:56PM

Registered Member #90 Joined: Thu Feb 09 2006, 02:44PM
Location: Seattle, Washington
Posts: 301

EvilTesla-RG wrote ...

I'd like to not have to be constantly turning my charging circuit on and off all the time. So, is there a way to add in a transistor or something so that when I flip the switch to turn on the SCR, it turns off my charging circuit until I release the switch?

I recommend a spring-loaded 2-pole double-throw switch with a center-off position. Push it upward and one pole (set of contacts) turns on the charging circuit. Release and it returns to all-off position with capacitors charged and waiting. Push it downward and the other pole fires the SCR.

Hey it's low-tech but really simple and extremely reliable!

Cheers, Barry
Nowadays the spelling "vampyre" is quite fashionable. Vampyres are obvyiously much more evyl and vycious than mere vampires.

EvilTesla-RG

Fri Jun 26 2009, 09:48PM

Registered Member #1523 Joined: Sat Jun 07 2008, 02:05PM
Location:
Posts: 97

Interesting, thanks.

I will be using photflash capacitors, ten of them to be precise. They will be chraged by a normal camera flash unit. So, it will be bettween 300 and 400 volts.

I havn't built the coil yet.

I am very sure the voltage is good. I am mostly worried about he amperage this SCR can take. It says that the peak amperage is 300 amps. I think this SHOULD be enough, but it is close, so i am not sure.

Saz43

Sat Jun 27 2009, 04:29AM

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

My coilgun is going to use a hearty mosfet to switch the power supply. I have a 3V source which will either gate the mosfet and connect the battery or gate the SCR. That way either only one or the other will be triggered. I have yet to test this.

Ebay is the way to go for obtaining SCRs. If there are not any immediately available, some will pop up soon.

EvilTesla-RG

Wed Jul 01 2009, 12:13AM

Registered Member #1523 Joined: Sat Jun 07 2008, 02:05PM
Location:
Posts: 97

Okay, I have bought a SCR, and I have found a switch that will work.

However, I have a problem.

I am starting to test my circuit, and as I have stated before I am using a camera flash charger.

This is the wierist problem. I will start to charge up my capacitors, and I will hear a whining sound, with an increasing pitch, as they charge up. But, around fifty volts, the pitch on the whining sound starts to go down, and the voltage drops back to zero.

I tried my circuit with a camera flash that was less heavily modified, and the whole thing worked fine.

However, I have made this particular circuit smaller, and would very much like to use it.

I am thinking maby the change in the way the pitch increases or decreases may sugest that it could be an oscilator problem.....

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