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Registered Member #3888
Joined: Sun May 15 2011, 09:50PM
Location: Erie, PA
Posts: 649
Ha! I use those same SCRs and I've mentioned them on here about a dozen times. Mentioned those diodes a couple times but I haven't used them yet myself (my free sample allowance from vishay seems to have expired.) Glad to see someone else trying them both out.
That's exactly how I'd calculate the gate resistor value, so I agree with the 75 ohms.
You're going to need a fairly large coil to get the peak current from even one of those caps down into the range that the scr can handle.
I've had success paralleling the 70tps12. Two ~1.5" lengths of ~1/8" thick by ~5/8" wide bars of copper were slotted across the thickness, near the end, spaced according to the distance between successive scr pins when they're butted together (front to back). The legs of three of the scr's were cut off near the base where they come out. The scr's were zip tied together and the stubs of the anode and cathode were soldered into the slots on the copper bars, with the excess length of the copper protruding from opposite sides. The protruding bit was then drilled so that heavy ring connectors could be bolted on. The gates each had their own resistor to balance out the current, with the other ends of the resistors all being tied together. I suppose a picture would show all of that at once, but I don't have a camera. A better explanation or a picture could probably be given if you're interested.
I've also found (possibly because of how the back emf/quenching works) that these scr's will fail if they are used at the positive side of the capacitor-coil circuit, so put them on the negative/ground side.
Registered Member #4237
Joined: Tue Nov 29 2011, 02:49PM
Location:
Posts: 117
Just follow the data sheet. Check out wikipedias article on them if you want to know how they work. If I'm not mistaken, the anode connects to positive, cathode to ground. When you apply a voltage to the gate, it will turn on. For example like this:
Registered Member #1525
Joined: Mon Jun 09 2008, 12:16AM
Location: America
Posts: 294
Tom Williamson wrote ...
how do you wire one of these SCRs, i tried and blew it, probibly got the wrong pins
im a total noob :(
I made a whole guide to designing SCR coilguns, I've been meaning to put it on a website but I just can't think of a name. Till then, I hope this will help:
Oh and please ignore the equation for the resistor, the one posted previously is correct.
Registered Member #3324
Joined: Sun Oct 17 2010, 06:57PM
Location:
Posts: 1276
im sorry, i didnt make myself clear >.<, i cant work out the pin numberings, ive got 50 different sites telling me different numbers and the datasheet isnt exactly clear x.x
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First Proper Coilgun
