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Okay, so I've read that people have used a setup of diodes to partially recharge the capacitors after firing. I cant remember where I read this, but the idea is to use diodes to take the negative pulse after your gun is fired and feed it back into the caps at the right polarity. Can you even do this, cause that's a really big pulse to be sending into capacitors, also, how would you even do that anyway?
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
I think I read a post along those lines. I don't think it was used to re-charge the capacitor, but to by-pass the capacitor, so the current keeps circulating through the coil.
It was a fairly recent post, I think, only a week or two ago. Shouldn't be too difficult to find.
No that's not it, I've read about that too though. I read about it some time ago, like 2 months back. I was just curious about how something like that would work. :)
Registered Member #90
Joined: Thu Feb 09 2006, 02:44PM
Location: Seattle, Washington
Posts: 301
You're thinking of a diagonal half bridge design. This is a bit more complicated than the usual single-SCR design because it requires two triggers to manage the timing. However, as you expected, it does recover the leftover energy and it does help turn off the coil at the right time. It can be built with an SCR, IGBT, MOSFET or other silicon devices.
It hasn't been done very often by coilgun hobbyists. Wouldn't it be nice if there were some motor-controller chip that can simplify the design? I've never looked into it, but it's a tantalizing prospect to adapt a good commercial controller chip to this purpose.
Registered Member #191
Joined: Fri Feb 17 2006, 02:01AM
Location: Esbjerg Denmark
Posts: 720
Same as the H-bridge, but each leg will have 1 diode and 1 switch. Also, if leg A has the switch on the high side, leg B will have the switch on the low side. hence the name diagonal half bridge.
Registered Member #90
Joined: Thu Feb 09 2006, 02:44PM
Location: Seattle, Washington
Posts: 301
Google is your friend.
One place to start is this simplified sketch from 4hv history. Note it does not show triggering circuits or component values.
In response to your original question: Yes, you can design circuits to recover leftover energy from current circulating in the coil. It requires active circuitry; no arrangement of diodes alone can accomplish the task.
Registered Member #1525
Joined: Mon Jun 09 2008, 12:16AM
Location: America
Posts: 294
Barry wrote ...
Wouldn't it be nice if there were some motor-controller chip that can simplify the design? I've never looked into it, but it's a tantalizing prospect to adapt a good commercial controller chip to this purpose.
There is such a chip, it's called a high side/low side driver. It's actually quite simple to implement for a coil-gun, not nearly as hard as some would make it seem. For example, the ir2110 which (even as a beginner) I have had great success with:
This guy built a nice half-bridge coilgun which gets 4.66% efficiency with one stage using a similar chip. He includes a schematic which shows that it's really not too complex.
Also, this guy built a 3-stage gun, which gets upwards of 10% efficiency in the half-bridge stages.
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Coilgun cap recharging?
