Choosing Capacitors for Railgun [was "Greetings..."] / Electromagnetic Projectile Accelerators / Forums

Forums

4hv.org :: Forums :: Electromagnetic Projectile Accelerators

« Previous topic | Next topic »

Choosing Capacitors for Railgun [was "Greetings..."]

1 2 3 4 next

Move Thread

LAN_403

Erg

Sun Feb 19 2006, 07:22PM

Registered Member #214 Joined: Sun Feb 19 2006, 07:01PM
Location:
Posts: 4

I just found out about this site and the possibility of making ones own railgun. I am very excited to be able to pursue an interest that I thought was out of my reach. I have access to a machine shop and a degree in avionics so most of the information I need is more railgun specific. I had a look at the local wiki and the forum and did not see the answer for my question. So, here goes. Will this capacitor be a good one to use in a rail gun?

Pyle PLCAP-50R 5 Farad Digital Square Style Power Capacitor
PLCAP-50R, PLCAP 50R, PLCAP50R
15.00" X 9.50" X 4.00"
5 Farad 24V double DIN amplifier style hybrid capacitor
Brushed anodized aluminum capacitor

I assume that I will need a largeish array of what ever cap I select and then set them up in paralell.
Would it also be a good idea to create a HV capable adjustable core inductor to lengthen the pulse discharge?

Additionally would it be a helpfull thing for me to post a few of the more usefull equasions/formulas I learned in school for electronics?

Any help is appreciated,
Thank you in advance,
Erg

[Mod edit: given more descriptive title.]

Marko

Sun Feb 19 2006, 08:10PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

This capacitor is car amplifier current booster, and 25V is far too low for high current discharging, resistance will be too high for it to operate normally.
It will give huge energy but slow and most will dissipate into heat, i wonder if it would actually move projectile rather than welding it.

If you have few of such caps maybe a 100 volt bank could be a try, energy is really huge but voltage low so results are questionable...

Im planing to use 350V 6000uF caps for railgun one day...

350V is best choice to charge from mains if its 220 or 200V if its 110V

Erg

Sun Feb 19 2006, 09:28PM

Registered Member #214 Joined: Sun Feb 19 2006, 07:01PM
Location:
Posts: 4

Thank you. I was trying to be carefull prior to buying something expensive. And since the capacitor deterimines so much about all else in this circuit I am shopping for them first.

Dave Marshall

Sun Feb 19 2006, 11:11PM

Registered Member #16 Joined: Thu Feb 02 2006, 02:22PM
Location: New Wilmington, PA
Posts: 554

Railguns are EXTREMELY difficult to get working satisfactorally with electrolytic capacitors. Typical railguns operate in the 2-5kv range, and use energy discharge capacitors to give a very high rise time. If you're going to use 'lytics, I would strongly recommend putting several in series to get voltage closer to 1kv atleast.

Most railguns I've seen that did use electrolytic capacitors in the 300-1200v range were really just spark shooters. Made alot of impressive sparks, but didn't have much output energy.

And being that you seem to be new to the hobby, please dont blow your fingers off with one of the caps (yes they will remove appendages).

Dave

Marko

Sun Feb 19 2006, 11:20PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

yep, but electrolytics are far easier to get (in my countra even in my town you can buy such high energy elko's)
Pulse discharge are more bulky and more pricy, but characteistics are overwhelming...

If you can find (lots) of dead defibrilators or so that is only place where you can get some at low or no cost, or try to catch something on ebay (far lower than market price but still expensive usually)

Maybe someone on this forum may even want to sell you such capacitor, for few hundred $ usually...

Erg

Mon Feb 20 2006, 03:35AM

Registered Member #214 Joined: Sun Feb 19 2006, 07:01PM
Location:
Posts: 4

First thank you for the safety warning, I can always be more safety concious. Who makes good Pulse discharge capacitors?

Dave Marshall

Mon Feb 20 2006, 04:39AM

Registered Member #16 Joined: Thu Feb 02 2006, 02:22PM
Location: New Wilmington, PA
Posts: 554

Cornell Dublier and Aerovox are the two that jump to mind immediately.

They can be found surplus, but as Firkragg says, they can be pricey. You wouldn't need more than one or two good size caps for a first try though.

There ARE pulse rated electrolytic capacitors available, and several such capacitors in series ought to be suitable for a first attempt at a railgun. They tend to be rare, and expensive, however. I believe most of the pulse rated 'lytics are inverter grade, and can be had on ebay if you watch. Characteristics to watch for include very large bolt terminals (all big capacitors use bolts, look for abnormally large terminals though).

Dave

Quantum Singularity

Mon Feb 20 2006, 07:08AM

Registered Member #158 Joined: Sun Feb 12 2006, 09:53PM
Location: Central Ohio
Posts: 282

I was under the impression that Maxwell Labs energy discharge caps were also excellent for this kinda work. I saw 2 at the dayton hamfest several years ago and bought them (actually there were three but I was a poor college kid and couldnt afford all 3). About 6kJ each. They have done excellent in my ring & disk launcher, can crusher, exploading wire... never did finish my railgun though. Surplus Sales of Nebraska has a page specificaly for Maxwells,

but I wouldnt pay those prices unless money is of no consequence to you. I also used a G.E. pulse cap on my bigger tesla coil and it has held up good.

Electroholic

Mon Feb 20 2006, 07:10AM

Registered Member #191 Joined: Fri Feb 17 2006, 02:01AM
Location: Esbjerg Denmark
Posts: 720

How about Maxwell? hehe
for lytics, the large photoflash lytics are good, too.
but they are very rare on ebay.
on and incase nobody have said this
"Try a coil gun first!"

Dr. Shark

Mon Feb 20 2006, 09:10AM

Registered Member #75 Joined: Thu Feb 09 2006, 09:30AM
Location: Montana, USA
Posts: 711

Actually I am under the impression that electrolytice are quite good for railguns, and as a consequence of this I replaced my bank of 35 40uF 2.5kV capacitors by a bank of 50 3300uf 350V electrolytics. The reason is simple: For a 1m railgun that accelerates a projectile to the speed of sound you want the discharge to take something like 5ms, _not_ 50us as you would probably get with a pulse cap.
The reason traditional railguns used those high voltage pulse caps is most likely that they are just what the military had available, and the price tag was not improtant for them. Also they were usually employing pulse transformers to lower the voltage delivered to the gun. Go figure.

I suggest you keep a look out for high voltage electrolytic capacitors, in the range of 300-500V and 3300uF - 12000uF (the higher the better). You want to do a bulk buy on these, keep a look on eBay, they can be had for few bucks / piece, so you will only pay a few 100$ for a decent sized cap bank.

1 2 3 4 next

Moderator(s): Chris Russell, Noelle, Alex, Tesladownunder, Dave Marshall, Dave Billington, Bjørn, Steve Conner, Wolfram, Kizmo, Mads Barnkob