First Coil Gun / Electromagnetic Projectile Accelerators / Forums

Forums

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

« Previous topic | Next topic »

First Coil Gun

1 2 next

Move Thread

LAN_403

cornerit

Wed Oct 12 2011, 04:18PM

Registered Member #4138 Joined: Wed Oct 12 2011, 12:52PM
Location:
Posts: 6

Hi,

First post here! You all seem like a friendly bunch of people and theres some decent information available here.

I am looking to build my first coil gun.

Parts I have acquired / waiting for delivery are:

'120uf 400v 105c Capacitor Radial 400KXW120M18X30' x 20 From ebay.

500G WINDING WIRE /MAGNET WIRE 1.18mm / 18.5SWG / 17AWG x 1 for coil.

A few disp. camera circuits.

I am not thinking of calculating lengths and much sizes at the moment as this is only my first attempt.

I am going to be charging the caps with the camera cirtuits which I know isn't the best thing but will do for now.

What I have been thinking is would a few basic switches be fine with this? I know they are not efficient but until looking into Coil Guns I had never heard of SCR's / relays.

Also I was wondering what the potentially dangers / pain could be inflicted from the 20 caps linked in par. if it was made contact with skin?

Do medical grade think latex gloves provide insulation to this kind of circuit and prevent a shock just incase?

I have searched around and found a few answers to other questions but hopefully you can give me a good insight.

Thanks

Forty

Wed Oct 12 2011, 10:15PM

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

Hey there
welcome to 4hv.
those capacitors, wire, and charger sound like a good start.
switches aren't a very good idea, as they tend to weld shut or explode. Using an SCR is very easy and you can get a few free from vishay

I've used this SCR extensively and with great results.
the left pin attaches to your coil (other side of coil connected to -capacitor), the middle pin to your +capacitor, and to the right pin connect a normally open switch (your trigger) to 2 AA batteries in series.

Getting shocked by a capacitor bank from arm to arm is probably not very healthy but i've done it before (400v, 2340uF.) It doesn't hurt so much as just scare the hell out of you as you get 'thrown' back.
The gloves should protect you just fine. It's also a good idea to wire in a discharge switch (a well insulated one) that just shorts the bank through a 1k to 5k power resistor. i've often run in to the problem while testing chargers (w/o a coil connected) of "ok, i've charged up the bank, now what?"

hope that helps, good luck.

cornerit

Wed Oct 12 2011, 10:52PM

Registered Member #4138 Joined: Wed Oct 12 2011, 12:52PM
Location:
Posts: 6

Thanks,

That link is most helpful, I will request a couple.

In terms of wiring, I understand the the coil and capacitor part but what about the right pin where does the other end of the trigger / batteries connect?

Why would people talk about linking multiple SCRS in one circuit? What can these SCRS handle ?

The discharge tip is good - I will bare this in mind.

One more question - What would be used in between caps / in the circuit to prevent the charge from going backwards and blowing the caps / causing damage? Would this setup be susceptible to that?

So there wouldn't be any risk other than a huge scare and being thrown?

You've been very helpful already so thank you!

Forty

Thu Oct 13 2011, 03:19AM

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

I definitely wouldn't say that there is no risk from the shock, but i know that it isn't 100% lethal.

the wiring would go from right pin ->one switch (momentary) terminal, other switch terminal to + side of two AAs in series, - side of the series battery to common ground.

that SCR will take a peak current in excess of 1400A for a 10ms duration. They're a little underrated, and your pulse will likely be shorter than 10ms, so they can probably be used up to a 2kA peak current. I've only killed one of them and that was because i overloaded the gate (the right pin)

multiple SCRs in a coilgun circuit are used either to fire multiple coils at different times, or to increase the overall current switching ability by placing them in parallel.
A diode placed antiparallel to the coil will fix the back emf problem. look up 'flyback diode' for an explanation as to why.
this diode should work (i might get some too actually)

2Spoons

Thu Oct 13 2011, 04:27AM

Registered Member #2939 Joined: Fri Jun 25 2010, 04:25AM
Location:
Posts: 615

Forty wrote ...

I definitely wouldn't say that there is no risk from the shock, but i know that it isn't 100% lethal.

A couple of uF charged to a couple of hundred volts can kill. It probably wont, but do you really want to take the chance? Treat everything over 50V as potentially lethal, that way you get to keep on breathing. There are no guarantees around electric shock, because every person is different.
Besides - pain is not nice.

ZakWolf

Thu Oct 13 2011, 06:50PM

Registered Member #3114 Joined: Sat Aug 14 2010, 08:33AM
Location:
Posts: 608

I Have a cap bank of 450v at 3600uf will one of those SCR's be suffecient ?

cornerit

Fri Oct 14 2011, 12:06AM

Registered Member #4138 Joined: Wed Oct 12 2011, 12:52PM
Location:
Posts: 6

Thank you,

Can you point me links of that scr on ebay (as needs to be paypal) or a suitable one,
Also discharge resistors and diodes to prevent caps and charger frying / blowing

Thanks

Forty

Fri Oct 14 2011, 01:08AM

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

cornerit: I gave a link to get the SCRs and diodes for free through vishay's sample program. The resistor can just be salvaged: look for a big white ceramic brick resistor with a resistance around 1k to 5k.

Sublime: It depends on your coil, since the inductance and resistance of it will determine the peak current. you could always parallel two of them to be sure they'll handle the current (with a resistor on each gate to ensure they trigger at the same time)

2spoons: A couple uF? yes i would take that chance lol. But by no means did i intend to make it sound as though cornerit's bank was safe to get shocked by, i just wanted to say it wasn't 100% lethal. When I'm working with new stuff i always like to know whether or not i'll die the first time i screw up, so i was just passing that along. Just be sure you never touch two parts of your circuit with separate hands (unless absolutely positive that it's all discharged, ie. power off doesn't mean safe)

ZakWolf

Fri Oct 14 2011, 02:44AM

Registered Member #3114 Joined: Sat Aug 14 2010, 08:33AM
Location:
Posts: 608

thanks

Legit_bacon

Sun Oct 16 2011, 09:00PM

Registered Member #4034 Joined: Thu Jul 28 2011, 10:41PM
Location: somewhere in the Southern hemisphere
Posts: 138

A good safety tip when working with charged caps: ALWAYS use one hand, the last thing you want is to stop your heart (bearing in mind they're prity much a difibulator). And forty, bloody hell 400v at 2340uf has gota damn hurt, worst I've had is 400v at 1000uf, yea does tend to kick! Good luck with your coil gun anyways.

1 2 next

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