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Coilgun showcase and help required

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guitarlord66

Wed Feb 09 2011, 01:24AM

Registered Member #1805 Joined: Sat Nov 08 2008, 06:29AM
Location:
Posts: 67

Hello :)

I had dropped out of the electronics scene for over a year, but I've been back for around 6 months, dwelling these forums and reading all the latests posts just as I used to. I had a lot of coil gun stuff uncompleted when I gave up, so I had a head start when I came back.

Now I realize I'm going to be flamed for this but at the moment, I am using disposable camera charger circuits to charge my coil guns...

I pretty much completed my latest coil gun, that I called "EMPA-III-NV" (Electromagnetic Projectile Accelerator 3 Night Vision)

This gun featured the following:
10 paralleled Camera Circuits
14 330V 80uf Capacitors
Relay Switching
Laser
30mm 8 layers 20 gauge enameled wire coil
Battery was 4.8v NIMH battery pack, but I fired the gun around 15 times and it overheated and cooked... So the guns out of operation at the moment...
an Analog meter that displays charge level
A very old Digital Camera from around 2000, that I converted to see IR light
A bank of IR LED's for the camera
Custom hand made plexiglass case
various switches, LED's, etc....

Heres some pictures, sorry for the low quality...

So its pretty much just a simple coil gun, that features a night vision camera and has the power to shoot through 3 empty soda cans. But as I said out of operation until I get a new battery source...

So, onto my next project that I'm having troubles with and wanted to ask for help...

I'm building a coil gun, that features a cylinder, from a toy cap gun, that will be able to hold 8 shots.
Now this coil gun will be even more unique because it features 2 banks of chargers and capacitors rather than 1.
My idea is to have 2 momentary switches on the back of the gun, along with 2 LED's above them.
The only way to fire the gun is to hold down one of the switches, that connects the capacitors of one of the banks to the coil.
The reason for having 2 charging circuits is so I can monitor the banks separately because they wont be discharged together.
This way I can fire twice before a recharge.

I originally intended to have 3 banks but after I wired it all up, I tried to discharge bank 1 and all the charging circuits overloaded and bursts with sparks of blue and smoke...
I have now made 2 more charging units but they are the last of the camera circuits that I have... I don't want them to meet the same fate as their predecessors...

I tried drawing a schematic but it looks more confusing then anything...
Circuit

I warned you its horrible...
If anyone can make sense of that... Any idea why my chargers got destroyed when i tried to discharge a bank? I assume I need diodes but I don't know where...

Any help or comments would be very much appreciated :) :)

GhostNull

Wed Feb 09 2011, 07:09AM

Registered Member #2648 Joined: Sun Jan 24 2010, 12:45PM
Location: Australia
Posts: 291

Oversized pics DX

A boost converter or proper charge will probably be worth reliability and efficiency. The crappy disposable camera circuits could likely be a cause of your Ni-Mh pack dying, no offence. It's a shame to see such an awesome coilgun charged by DCC (disposable camera circuits). I like the night vision :D

Your new coilgun should work fine, just make sure those relays can handle the current. Flyback diodes on the relay coils would be beneficial for helping the switches and battery last longer but that's long long term; it will be completely fine without.

A schematic of the circuit would be beneficial in determining what went wrong. If it was a DCC it could be very likely due to the cheap, weak components. Diodes on the output of the charger circuits would prevent charge from the capacitors going back into the charging circuit but there should be a diode there already.

guitarlord66

Wed Feb 09 2011, 07:22AM

Registered Member #1805 Joined: Sat Nov 08 2008, 06:29AM
Location:
Posts: 67

Yeah this new one is the last disposable camera driven one I'm going to make, I just want to try this concept before I move on to boost or flyback charging.

I've never had to use diodes before, the ones in the circuits have always done the job for me. I have never had chargers burn out when I discharged the capacitors before, I've burnt out heaps trying to use higher inputs then they were made for but thats it...
Its just I already tried the schematic I posted and the chargers burnt out. I dont know why though, I think it has to do with the fact I had the (positive or negative I forget...) leads from both banks connected together at one end of the coil, I cant think of any other reason... well apart from the fact the banks are connected at the battery inputs... Maybe the capacitors and battery inputs are linked and thats what fried them... Any idea?

guitarlord66

Thu Feb 10 2011, 03:10AM

Registered Member #1805 Joined: Sat Nov 08 2008, 06:29AM
Location:
Posts: 67

Does anyone have experience with making a magazine for a coil gun? I thought using a revolver cylinder would be easier but I'm not so sure anymore...

aarpcard

Thu Feb 10 2011, 03:45AM

Registered Member #2848 Joined: Tue May 04 2010, 05:19AM
Location:
Posts: 44

My guess as to why your circuits fried is because when the projectile went through the coil after being accelerated, it induced a current back into the wire which then flowed back into your circuit which fried the chargers. I forget the technical terms for all of this. It's also quite bad for the capacitors hence the need for diodes.

Back when I was first starting my coil gun projects I used DCC circuits too and I had the same problem as you did for the reason I stated above. The best way to solve the problem was with diodes, or like I ended up doing, every time I fired the gun, I'd flip a switch which disconnected the charging circuits from the capacitor bank.

guitarlord66

Tue Feb 15 2011, 06:10AM

Registered Member #1805 Joined: Sat Nov 08 2008, 06:29AM
Location:
Posts: 67

I just thought I'd say, I found a rechargeable engraver that didn't work too well so I took the batteries out and put them in the coil gun shown above. The batteries charged for an hour, I think they were done because the voltage didn't go up any higher than 4.31 volts. I don't know what kind of batteries they are because they are unlabeled but I know they have 3 "cells" if thats what you call them. Anyway the gun charges in 10 seconds! with the old NIMH it charged in 15 to 20 seconds and there were 4 "cells" in the NIMH pack, but the batteries get hot, so I'm thinking I'll shoot it 3 times and let it cool? I really need some help with why batteries get hot and how to prevent them from cooking to death... I assume that its either too much power is getting wasted and converting to heat? or the batteries are not made to discharge as fast as I want them to? Any help is very much appreciated with this problem :)

guitarlord66

Thu Feb 17 2011, 05:31AM

Registered Member #1805 Joined: Sat Nov 08 2008, 06:29AM
Location:
Posts: 67

Would this be any good for a coilgun discharge or in a cap charger?

I found it in an old tv :)

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