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New Coilgun plans..need feedback

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Cwazy

Mon Nov 12 2007, 09:36PM

Registered Member #1106 Joined: Thu Nov 08 2007, 01:15AM
Location: Seattle, Washington
Posts: 25

So i plan on adding onto my current coilgun by adding caps. This is going to be a low voltage settup. i will be using (8) 15v 100,000uf caps linked together in parellel charged to 12v. when i do the math, i get 57.6J energy and then with a 1% efficiency and using a 6g 1"x1/4"projectile, i get 13.6m/s. i am planning on justing a heavy duty toggle switch to trigger the caps. the charging will come from my current settup, which is 2x 12v batteries. as for the coils, i am going to use fat coils so it'll be either 12 or 14 gauge.

so for the coils, how many turns should i turn so i get the most power? and what do you guys think about this settup? good/bad? is it worth the extra 40$ i would have to put into it?? and ****how would it compare to my current coilgun??****

***my current gun is (2) 12v lantern batteries hooked in parellel shooting a 6g projectile. i am using a push button trigger and is very inaccurate.***

Shaun

Mon Nov 12 2007, 09:51PM

Registered Member #690 Joined: Tue May 08 2007, 03:47AM
Location: New Jersey, USA
Posts: 616

First of all, it would be a lot better than your first coilgun. You really can't compare batteries to capacitors in terms of high-amp discharges; capacitors are just so much better.

You calculated projectile velocity with an estimated 1% efficiency. This will be harder than you think to achieve using a toggle switch, big as it may be. This is really SCR territory.

In terms of coil size, many people believe your coil should be about as long as your projectile. You will probably want 6 or 7 layers, too, and work from there to see what improves performance.

Cwazy

Mon Nov 12 2007, 10:00PM

Registered Member #1106 Joined: Thu Nov 08 2007, 01:15AM
Location: Seattle, Washington
Posts: 25

ahh, so you say that with a toggle switch wont even yeild me 1% efficiency?? if so, i want good efficiency/power, so i should use a scr to trigger yes? and with my caps, what would be the best scr for me?

and also, what about diodes?? do i have to have one?

Shaun

Mon Nov 12 2007, 10:49PM

Registered Member #690 Joined: Tue May 08 2007, 03:47AM
Location: New Jersey, USA
Posts: 616

A toggle switch *might* yield 1% efficiency, depending on a range of factors. Any type of SCR will be better than your switch, by far. Preferably one of the heavier screw-mount ones, but a couple T0-220 devices in parallel could work, too.

You absolutely MUST have have a diode. If you apply voltage to an inductor (your coil), when you take away that voltage the coil will produce a higher-voltage spike of the opposite polarity. Electrolytics HATE reverse polarity as much as they do higher voltage. A diode will short out this back pulse, protecting your caps.

Cwazy

Tue Nov 13 2007, 01:41AM

Registered Member #1106 Joined: Thu Nov 08 2007, 01:15AM
Location: Seattle, Washington
Posts: 25

shaun, i just noticed that it was you that i was talking to last night. lol

so heres a basic diagram that i drew up on paint. where am i suppose to stick the diode?

Shaun

Tue Nov 13 2007, 01:53AM

Registered Member #690 Joined: Tue May 08 2007, 03:47AM
Location: New Jersey, USA
Posts: 616

It should look like this:

It will need to be able to handle more than a few amps pulsed. A regular 1N4007 will not do...think like 5 in parallel or more.

Cwazy

Tue Nov 13 2007, 02:08AM

Registered Member #1106 Joined: Thu Nov 08 2007, 01:15AM
Location: Seattle, Washington
Posts: 25

so like ten of these little suckers in parellel would do the job?
http://cgi.ebay.com/1N4007-Diodes-1-amp-1000v-on-tape-200pcs_W0QQitemZ290178735726QQihZ019QQcategoryZ7287QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

and also, the ->|- on ur picture, .....is it (-) ->|- (+) for the diode direction??

Shaun

Tue Nov 13 2007, 02:18AM

Registered Member #690 Joined: Tue May 08 2007, 03:47AM
Location: New Jersey, USA
Posts: 616

Exactly. The diode should "point" to the positive of the capacitor. And about those diodes...they would work great. I should add that some people feel better using ultrafast diodes (UF4007, UF4005, etc) but I have always used 1N4007s with no problems.

Plus having all those extra diodes is a good thing; they come in handy.

Cwazy

Tue Nov 13 2007, 02:48AM

Registered Member #1106 Joined: Thu Nov 08 2007, 01:15AM
Location: Seattle, Washington
Posts: 25

ahh sweet. so is there anything missing from my drwaing that i would need to know about?? oh and btw, does anyone know the uf of my batteries? or if it even has one? i would like to do some calculations..lol

rp181

Tue Nov 13 2007, 03:03AM

Registered Member #1062 Joined: Tue Oct 16 2007, 02:01AM
Location:
Posts: 1529

i dont think im getting this. If you use 800,000 uf for your caps, wont that make the pulse too long and reverse the effect? i thought you kept this low and got voltage high.

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