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Registered Member #27
Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058
You need highest possible current and lowest possible friction. If you can't measure the current then you are working blind. If you don't know the ESR of your capacitors then only luck can make you succeed.
To reach your target with such a low energy you need a well made railgun. I suggest that you make an efficient coil-gun first to learn more.
Registered Member #33
Joined: Sat Feb 04 2006, 01:31PM
Location: Norway
Posts: 971
If you have five 80µF 60V caps, as you stated in your first post, then you have 0.72J in total. If you had a hundred times this, it might be possible. If you had a thousand times this, it should make a usable small railgun. Unless you can get several hundred of these caps, I'd start looking for some better caps.
Registered Member #69
Joined: Thu Feb 09 2006, 07:42AM
Location:
Posts: 116
Photo flash caps are 'good' in that they have low ESR and are designed for high current output but you should be able to use just about any electrolytics. You ought not to need more than 300V-400V if your circuit resistance and inductance is kept to a minimum. Most people use big filter capacitors from switching power supplies. They are easy to find on ebay.
The big limiting factor with electrolytics and railguns is their high ESR, so generally you'll be better off with caps wired in parallel. Caps should have a voltage rating in the ballpark of 300V-600V.
As others have said, steel rails are very bad. They have high resistivity and also very high AC resistance due to skin effect in comparison to copper. The net effect is that they are ~100 worse than copper and will limit your peak current.
Registered Member #600
Joined: Thu Mar 22 2007, 08:41PM
Location:
Posts: 10
Aluminium is a good alternative if you can't find copper, it is a lot easier to find at an affordable price, but it is still better than steel. Try googling for statistics of different materials - electric conductivity, melting point, etc. The only way to find out how these numbers combine in real life though is to try it out.
Registered Member #608
Joined: Wed Mar 28 2007, 12:01AM
Location: Canada
Posts: 17
I have aluminum rails i can use instead of steel (15 inches each) and i have found cheap caps that have a voltage rating of 330v and 120uf each. I am using speaker wire to connect my caps to the camera flash board and the rails. How many caps of 330v and 120uf would i need to fire my projectile (small piece of aluminum, until i can find a more effecient projectile) 5-10 feet?
Registered Member #600
Joined: Thu Mar 22 2007, 08:41PM
Location:
Posts: 10
It would be impossible to predict that due to the number of different factors that would need to be considered. Use the fattest cable you can obtain, and perhaps 30 photoflash capacitors. If range is all that matters, use a slightly smaller piece of aluminium foil. As it weighs less it will be go faster, within reason. Try all different shapes, sizes and materials for the projectile, be creative :)
Registered Member #600
Joined: Thu Mar 22 2007, 08:41PM
Location:
Posts: 10
For lower energy levels, you can use silicon controlled rectifiers to switch power, search the forums and you'll find a few topics about them, and other ways you can improve efficiency, also make sure that your setup is safe - especially protect yourself from unexpected shrapnel from the circuitry, check the voltage on the capacitor bank before touching anything, etc, you can never be too careful.
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