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Registered Member #4343
Joined: Mon Jan 16 2012, 01:45AM
Location: Florida
Posts: 10
Hi all, I am considering building a rather large coil gun, something on the order of 12+ farads. I have built a smaller coil gun successfully, so I have some experience. My question is: where can I get a charging circuit for my capacitor bank? I plan on using a combination of 400v 1000µf capacitors, and some 330v photoflash caps, all connected in parallel. I need a circuit that I can use to charge the whole thing up to 330v with fairly quickly, but would be capable of charging the 400v caps by themselves, too. I don't want a disposable camera circuit board, because it would take forever to charge a capacitor bank that size. Also, where could I (inexpensively) get a converter to plug into a wall outlet that I could connect to the circuit and use to charge the coil gun? Thanks.
Registered Member #4497
Joined: Thu Apr 19 2012, 12:53PM
Location: Behind you
Posts: 62
so, you are planning to build 12F 400V cap bank? lol, that's almost 1MJ of energy, the only way how to charge it is from rectified outlet, so it'l be 350V if you have 230V outlet, and because 960kJ are 2.6kWh, it will take more than hour to fully charge it...
Registered Member #72
Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659
Let's see if I have this right. You're going to build a 12F capacitor, and charge it to 330v?
I make that 650kJ. If you charge that at a constant 3kW (probably about the largest thing you'd want to plug into a wall), it will take over 3 minutes at 100% efficiency. I agree the impracticality of a camera flash board, you'd plug it in and then have to go on a 3 week vacation.
Did you mean 12mF = 12,000uF? It would take more than a 3 week vacation of soldering to make a 12F cap with 120k parallel 100uF PFCs, though it's only 12k of the 1000uF ones if you have a majority of those. Whichever caps, it's going to end up as a cube more than 1m on each side, and weighing more than 1 tonne.
Registered Member #4343
Joined: Mon Jan 16 2012, 01:45AM
Location: Florida
Posts: 10
Dr. Slack wrote ... Did you mean 12mF = 12,000uF?
Oops, sorry. Yes, I did mean that. I have a bad habit of getting distracted while I'm typing and leaving out words. I plan on connecting 12) 400v 1,000µf capacitors, along with some photoflash caps from Walgreens. If it isn't too difficult/expensive, I wouldn't mind making my own charging circuit But keep in mind that I'm not exactly an engineer or anything.
What? Someone told me that you couldn't build a coilgun out of flash board caps! Oh wait... hm, how much were those 400V 1000uF caps? Heh, that will make one helluva bang if you discharge it across the terminals... I hope you have a huge area to eject a piece of metal. Killa-X did his in his room and caused a hole to appear on his door.
@Microfarad: What part of Florida are you from? I'm from orlando. We should start a coilers group :P
Registered Member #4343
Joined: Mon Jan 16 2012, 01:45AM
Location: Florida
Posts: 10
HighVoltageChick wrote ...
What? Someone told me that you couldn't build a coilgun out of flash board caps! Oh wait... hm, how much were those 400V 1000uF caps? Heh, that will make one helluva bang if you discharge it across the terminals... I hope you have a huge area to eject a piece of metal. Killa-X did his in his room and caused a hole to appear on his door.
@Microfarad: What part of Florida are you from? I'm from orlando. We should start a coilers group :P
Yes, you can build a coil gun out of flashboard caps. That's what I used for my little coilgun. I had 28 of them, all wired in parallel. It came out to 2.88 millifarads, and cost ~$20, since I got all the caps free. I can get it shoot a 0.177" steel bb about 50-80 feet, but it needs a full six minutes to charge up with a flashboard charger. That's why I need something much faster for this project. I plan on using a 1/2" (.50 caliber! ) steel ball bearing as the projectile, unless I find somewhere to get 1/2" iron bars. (I prefer not to use rebar, because it doesn't have a smooth surface.) I will definitely be firing it outside! I don't remember how much those caps were; I'd have to find them again. But I can tell you, they are not cheap, or I would buy more of them. I'm kind of near-ish to the Tampa area, BTW.
Registered Member #3900
Joined: Thu May 19 2011, 08:28PM
Location:
Posts: 600
iron or thick iron or steel nails work well. on some thick screws, they have a smooth section with no thread just before the head. i like to cut this out, then grind it into shape. on a quick lashup i did a while ago, no calcualtions/tuning or anything, i got one of these clear through a soda can.
What? Someone told me that you couldn't build a coilgun out of flash board caps! Oh wait... hm, how much were those 400V 1000uF caps? Heh, that will make one helluva bang if you discharge it across the terminals... I hope you have a huge area to eject a piece of metal. Killa-X did his in his room and caused a hole to appear on his door.
@Microfarad: What part of Florida are you from? I'm from orlando. We should start a coilers group :P
Yes, you can build a coil gun out of flashboard caps. That's what I used for my little coilgun. I had 28 of them, all wired in parallel. It came out to 2.88 millifarads, and cost ~$20, since I got all the caps free. I can get it shoot a 0.177" steel bb about 50-80 feet, but it needs a full six minutes to charge up with a flashboard charger. That's why I need something much faster for this project. I plan on using a 1/2" (.50 caliber! ) steel ball bearing as the projectile, unless I find somewhere to get 1/2" iron bars. (I prefer not to use rebar, because it doesn't have a smooth surface.) I will definitely be firing it outside! I don't remember how much those caps were; I'd have to find them again. But I can tell you, they are not cheap, or I would buy more of them. I'm kind of near-ish to the Tampa area, BTW.
I see. But what cost the other 20 dollars? Heh, I don't have money on me, I wish you could build one out of pure flashboard caps. I have access to tons and tons and tons of them. I have ~30-50 lying around, and I can get ~2-8 each time I go to the photo center (of course, living in orlando means that they come in by the truckload to the stores for quick development) so to make a legitimate coilgun (IDC how far it propels the slug, as long as it does something) how many would I need? 20? 50? 100? and what would I need for a power supply?
Tampa is nice. I like Busch Gardens. Been on the Cheeta Run or something? I went on a fieldtrip to there... a week before the ride opened. Band teacher trollface. :P
Registered Member #4343
Joined: Mon Jan 16 2012, 01:45AM
Location: Florida
Posts: 10
Most of the cost of my coilgun was nonessential components. I added lots of extra safety and configuration switches that were not necessary, but made the coilgun a little cooler. I also spent a few dollars on wood to make a housing. If you made it as bare bones as possible, the only things you would need besides capacitors and a charger would be a switch to fire it (connect the coil to the ends of the flash tube, and put the firing switch in one of the leads of the coil), a charging switch, the wire for the coil ($7 for a package of three different guages I think, at radioshack, but I got two packages so I could have twice the length of 20AWG that came in one pack), and a barrel. I used the packaging for a little brass rod I got at Ace hardware, which was a nice little plastic tube. A soda straw will work, just be careful not to wind the coil so tight it crushes the straw. You could put a dowel in it to help it keep its shape while you wound the coil, so you could still wind it tightly. I built my coilgun with about 30 capacitors, which came out to 2.88 millifarads, as I mentioned earlier. For a power supply, I used a D cell battery hooked up to the battery terminals on the board, but I would recommend finding an adapter that will allow you to plug it into the wall, as I only got about 4 shots out of one battery.
Any ideas on the charger, anyone? Pinkamena, I read that thread you posted the link to, but I didn't understand most of it. (like I said, I'm not exactly an engineer) If possible, I would like to get a pre made unit. After all, if such capacitors are available, surely there are chargers for them. I just can't seem to find any.
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Capacitor charger for coil gun?
) steel ball bearing as the projectile, unless I find somewhere to get 1/2" iron bars. (I prefer not to use rebar, because it doesn't have a smooth surface.) I will definitely be firing it outside!
