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coil gun, cooling down the coil(s) with peltier(s) or maybe even liquid nitrogen.

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LAN_403

DÃ©dÃ©!

Tue Jan 07 2014, 09:00PM

Registered Member #4932 Joined: Thu May 17 2012, 01:42PM
Location:
Posts: 59

Hi, I'm building a coil gun and I was wondering since current is important and end irons and an iron pipe around the coil can increase the amount of energy converted into kinetic energy, but also allows the coil to overheat faster, can cooling down the coil with 1 or more peltiers or even liquid nitrogen, help without damaging the coil or any other parts? maybe silica gel can prevent water from condensing in the coil or around the coil itself. maybe you can even increase the heat transfer inside the coil with a small amount of thermal paste. I can't write more, because my MUM is annoying and wants me to go to bed!!

DerAlbi

Wed Jan 08 2014, 12:07AM

Registered Member #2906 Joined: Sun Jun 06 2010, 02:20AM
Location: Dresden, Germany
Posts: 727

What mass has your Coil? What heat capacity has copper? How much energy will be disipated in joules?
How high the temperature will become?
How old are you?

DÃ©dÃ©!

Wed Jan 08 2014, 11:42AM

Registered Member #4932 Joined: Thu May 17 2012, 01:42PM
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Posts: 59

I don't have a coil yet and the heat capacity of copper can be found on wikipedia. It's not that high.
I don't know the amount of energy that will be dissipated in joules, but I can find cheap 5W peltier elements for â‚¬5,- each. They are 15x15x4.9mm. the highest temperature difference of those peltiers is about 60K. I was thinking about putting 2 on each side of the coil, next to the end iron with a piece of metal on the hot side of the peltier too and filling the gaps with some insulation and ofcourse put some thermal paste on the peltier.
I'm 16 years old and I wasn't yet planning to do this. I'm first going to finish my coil gun and maybe I can make a second coil with which I do do this. I was just asking, because IÂ´m curious what could be possible, how significant the difference in both temperature and resistance could be and if it would be a good idea.

Shrad

Wed Jan 08 2014, 12:27PM

Registered Member #3215 Joined: Sun Sept 19 2010, 08:42PM
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Posts: 780

if you cool down coils with TECs, you have to mold them in thermal epoxy and have a flat bond with the TEC

DÃ©dÃ©!

Wed Jan 08 2014, 01:43PM

Registered Member #4932 Joined: Thu May 17 2012, 01:42PM
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Posts: 59

ok cool! So it's very well possible, but do you know if it has ever been done? also as a thermal epoxy, do you mean something like this?
http://www.omega.com/Temperature/images/OB-100_OB-200_OT-200_l.jpg
Do you know if the difference between a TEC cooled coil and a normal coil is significant, or do I have to try it out and post the results here? or maybe someone else can try it out? This is of course if it's never been done before.

DerAlbi

Wed Jan 08 2014, 03:08PM

Registered Member #2906 Joined: Sun Jun 06 2010, 02:20AM
Location: Dresden, Germany
Posts: 727

Well.. you know... you ask too quickly

You are concerned about "...the coil to overheat" and yet dont even know how much energy you actually convert into heat nor you know what this energy does to the coil. You dont know your coil geometry and nothing.
You solve practical porblems without having the actual problem :-/
You think about resistance and stuff without knowing yet how it will influence the accelerator at all..

Then you talk about peltier elements with 60K dT.. and you seriously think you can attach them onto you coil.
You are cooling a massive body with a huge surface. You know what kind of power will be needed to keep the coil cooled? Can the Peltiers deliver that???
So why actually you think about thermal paste at all?

What i mean: you think way too far. Practiacally all of your thoughts wont even make it past a sheet of paper - if you would actually calculate somehting instead proposing wildly.

You may search the internet for Coilgun projects. You see what has been build and mostly what the design is capable of. Start there, and not try to improve a project that doesnt exists.

Other question: why do you think lowering the resistance will make a better performance?
How much resistance change do you expect?
...ahh right, you dont even have a coil to get a resitance value......
Halving 20Ohms will still suck.
Halving 20mOhm will still make no practical difference.
Did you decide what circuit topology you want to build? (Halfbridge, critically damped or diode clamped?)

DÃ©dÃ©!

Wed Jan 08 2014, 03:56PM

Registered Member #4932 Joined: Thu May 17 2012, 01:42PM
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Posts: 59

I know I don't have a coil yet and don't come with any numbers about the coil, but I'll wind my coil in a couple of weeks (max. 3), after I've done my charger. it's Uzzors' ZVS charger. Also, if the heat produced by the coil isn't significant, cooling the coil down can still decrease resistance, but I don't know if it's by much. If the amount of heat produced is really high, and the peltier can't handle it while running, you can still cool down the coil before use (and even during use) and you can cool the coil down after or in between usage.
On a less related note, I have a 400V 11200ÂµF cap bank and I'm looking for an SCR at the moment.
http://www.vishay.com/docs/94382/180rkipb.pdf
I think this one is a good enough SCR, but don't know 100% sure. can you check? I know I don't have a coil yet, but I also know my caps won't discharge faster than a millisecond.

BigBad

Wed Jan 08 2014, 04:48PM

Registered Member #2529 Joined: Thu Dec 10 2009, 02:43AM
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Posts: 600

Peltiers? Nahhhhhh.

On the other hand, precooling your coils with liquid nitrogen is an EXCELLENT idea!

The resistance of your coils are massively reduced at LN2 temperatures; like 80% reduction. You'd be looking to improve efficiency and kinetic energy by equal measure.

DÃ©dÃ©!

Wed Jan 08 2014, 05:03PM

Registered Member #4932 Joined: Thu May 17 2012, 01:42PM
Location:
Posts: 59

I like liquid nitrogen, but it's pretty expensive and doesn't last forever. peltiers can last a long time and the electricity needed to power them is nearly free. Also, if you can get your hands on liquid nitrogen and get your hands on some superconductive wire for higher temperatures than 63K, you can even wind a super conductive coil! In that case voltage matters a lot less and capacity matters a lot more. Also, if you've cooled your coil with liquid nitrogen, you can still use the peltiers to sustain the temperature a little bit.

Ash Small

Wed Jan 08 2014, 07:06PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

You are likely to run into other problems at LN2 temperatures, mainly contraction related. Your barrel diameter could shrink, if your coils are epoxy potted they will shrink/go brittle, etc, etc.

You'd probably be better off spending your cash in other areas, although I'm not trying to 'put you off', just suggesting your money may be better spent elsewhere in the coilgun to increase power/efficiency in other areas.

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