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What are the voltage and capacitance on your coilgun(s)?

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Yanom

Wed Jun 27 2012, 10:03PM

Registered Member #4659 Joined: Sun Apr 29 2012, 06:14PM
Location:
Posts: 158

I've built a super-small 50v coilgun, and it launches an iron nail 30cm or so. Now I want to build a bigger one. What voltage do your coilgun(s) operate at? How much capacitance do you use? Also, I'd like to know about your coils. What wire gauge? How much wire?\

Thanks.

genious 7

Thu Jun 28 2012, 12:50AM

Registered Member #2887 Joined: Sat May 29 2010, 11:10PM
Location: Panama City, Panama
Posts: 107

I haven't personally built one, but I can tell you people use way higher voltages, some people even use ~400v. Many also use ~300v, as that's the rating of camera flash capacitors. Others who have experience in this field will be able to tell you more.

Forty

Thu Jun 28 2012, 03:18AM

Registered Member #3888 Joined: Sun May 15 2011, 09:50PM
Location: Erie, PA
Posts: 649

300v to 400v
as much capacitance as you can get
largest wire you can find (I use 16awg)
coils should be about the length of your projectile (+/- 25%)
Number of layers depends on a lot of factors, but i usually use between 4 and 7

Yanom

Thu Jun 28 2012, 03:38PM

Registered Member #4659 Joined: Sun Apr 29 2012, 06:14PM
Location:
Posts: 158

Forty wrote ...

300v to 400v
as much capacitance as you can get
largest wire you can find (I use 16awg)
coils should be about the length of your projectile (+/- 25%)
Number of layers depends on a lot of factors, but i usually use between 4 and 7

Oh... I'm using a coil with waaaaaay more turns than that - 140 Meters of 24AWG coiled up in a spool the size of a soda can. it's got 11ohms of resistance; what's the resistance on your coil?

Ben Solon

Thu Jun 28 2012, 06:31PM

Registered Member #3900 Joined: Thu May 19 2011, 08:28PM
Location:
Posts: 600

The idea is to get the highest amperage possible flowing in a certain time period. You want low resistance. Use Barry's simulator and change the stuff around to get the max current and minimum reversal.

Forty

Thu Jun 28 2012, 06:33PM

Registered Member #3888 Joined: Sun May 15 2011, 09:50PM
Location: Erie, PA
Posts: 649

play around with the simulators here. Simulate a coil with the inductor sim, then plug those values into the RLC sim along with capacitor values to get a picture of the pulse you're making.

The rest involves a lot of guess work (unless you've got the proper measuring equipment) but I usually pick an efficiency range I'd like to fall into, multiply that by the energy stored in the caps, set this value equal to the KE of the projectile, and from that and the mass of the projectile, then find an estimated final velocity.

you'll then want the time of your current peak to coincide with t=2x/v where x is the distance from the center of the projectile in its initial position to the center of your coil and v is the estimated velocity.

Since the calculated method will likely never give you the best actual values, your best bet is just to wing it.
Make a reasonable coil (yours is not, lol,) make a bunch of near identical projectiles, and experiment with initial position, capacitor bank size, and charging voltage until you get the best results.

From some rough guessing, and using Barry's inductor sim, my coils are probably all (except one) around 50-150 milliohms and use 5-10m of wire (that seems a bit high though.)

Pinkamena

Fri Jun 29 2012, 04:26PM

Registered Member #4237 Joined: Tue Nov 29 2011, 02:49PM
Location:
Posts: 117

Well, I haven't built mine yet, but I am in process of doing it. The cap bank will be charged to 270V. I would have preferred a much higher voltage, perhaps around 800V, but my caps are rated at 300V max. It has a total capacitance of 98.5 mF. When designing your coil, you want it to use all the energy in your capacitors in the same time span it takes for your projectile to reach the center of the coil. As stated above, Barrys simulator is a good starting position.

Barry

Sun Jul 01 2012, 03:59AM

Registered Member #90 Joined: Thu Feb 09 2006, 02:44PM
Location: Seattle, Washington
Posts: 301

10 - 20v
as much capacitance as you can get (24,000 uF is nice at about 1.5 joules)
largest wire you can find (I use 12 awg) surrounded by transformer iron leaves
coils should be about the length of your projectile (+/- 10% including surrounding iron))
Number of layers depends on the desired inductance, but i usually use between 1 and 4

This is for my Mark 3 coilgun, which gains efficiency in energy conversion by shooting at low energy. I'll try higher energy with a later model.
Cheers, Barry

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