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I have started building these things using Camera capacitors, and I have a bank that is about 1.2kj, but after my 15th camera charging circuit blew today with i have decided that I need to move away from cameras.
I was thinking that I want to build something with the large electrolytics but I do not know where to buy them, how to charge them, and what I need to safely trigger them.
The mechanics of the guns are easy as I work in a machine shop, but any help is appreaciated.
Registered Member #902
Joined: Sun Jul 15 2007, 08:17PM
Location: North Texas
Posts: 1040
you can buy the capacitors from a lot of places, but it really depends on what kind of Energy you are looking for ( PE = 1/2 * C * V^2 ) - so depending on what values you end up using you may be able to harvest from objects, or have to order online...
I currently get my caps from ebay, ( 5600 uF @ 500V) and if this is your first time custom building a Bank, Charger, and Firing mechanism I personally do not recommend caps with 700 Joules a piece If I remember Alltronics also has some decent caps
but for a first time complete build, maybe you should stick with your photoflash caps and build a custom charger and firing switch so that you can get a feel for how things work without shelling out money for big caps when you have never built a coilgun all the way from the ground up before
as for charging, again it will depend on your desired voltage and overall Energy - if you kept using your photoflash capacitors in a large array of, say, 300V then you could use a Boost Converter or possibly a transformer (do keep in mind to put diodes to prevent a reverse pulse from entering your charger, and that may be why your cameras keep failing - coil guns can kick back quite an electrical spike and the diodes keep this spike from damaging your capacitors and charger circuit)
and for firing, an SCR is most commonly used - or if you use an IGBT of appropriate ratings you could actually control the duration of the pulses from the bank to get optimum results, more energy is not better if you don't use it right
if you are unfamiliar with these things then I highly recommend you do some research - google helps, though I do understand there are so many coilgun designs that it may be confusing at first. Also the Wiki here has some information that might be very useful to you.
as for the ETG, I recommend you wait on that until you have more experience with Pulse Power
The voltage of a capacitor (and of the charging circuit obviously) is of utmost importance, as it is squared!
So you should go for a voltage of 450V (which is very common) or 500V (quite rare) or something like that.
The capacitance then should be the greatest available at this voltage (maybe 600 uF or sthg like that).
The cost would be about 40-60 $ each, and you need a few (3-4 or more) in order to build a gun with ballistic energies available - that doesn't mean ballistic velocities though!
E-bay has some stuff but NOT that many, although a search on ebay will give you some interesting links of sponsoring webpages that sell electronics.
Registered Member #902
Joined: Sun Jul 15 2007, 08:17PM
Location: North Texas
Posts: 1040
kromsson wrote ...
The voltage of a capacitor (and of the charging circuit obviously) is of utmost importance, as it is squared!
So you should go for a voltage of 450V (which is very common) or 500V (quite rare) or something like that.
The capacitance then should be the greatest available at this voltage (maybe 600 uF or sthg like that).
The cost would be about 40-60 $ each, and you need a few (3-4 or more) in order to build a gun with ballistic energies available - that doesn't mean ballistic velocities though!
E-bay has some stuff but NOT that many, although a search on ebay will give you some interesting links of sponsoring webpages that sell electronics.
600 uF at 450V would only be 60 Joules, very low - you used to be able to get 1.2 kJ from Alltronics for about $30, but that deal may be gone - and caps of decent rating will not cost that much each, even in store locally I would never pay that much (I think it is between $5 and $10 for a decent 400V one)
Registered Member #2400
Joined: Mon Sept 28 2009, 10:04AM
Location: Bundaberg, Australia
Posts: 18
Hey, to charge my capacitors i use the circutry from a 12v compact fluoresent light. These have a compact inverter which you can rectify with some diodes. It charges my 80J capacitor bank to 400v in 20s so maybe 2 or more in parrellel would help.
Registered Member #2393
Joined: Sun Sept 27 2009, 07:36AM
Location: Central Victoria, Australia
Posts: 7
Televisions usually have ~400V, 220uF's in them, if you have old TV's lying around, (as everything's going digital, there should be a pile of oldies in any western city...). I volunteered some time recycling old TV's and computers a while back, got 'puter fans, heatsinks, flybacks, and caps...:-D great place for parts.
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Help, Building Coil Gun/ ETG
