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My first 'real 'coilgun

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Hanzie

Sat Dec 08 2012, 04:38PM

Registered Member #6534 Joined: Sat Sept 08 2012, 12:22PM
Location: The Netherlands
Posts: 32

Hey all!
I've been doing some things with electronics for a while , and have been in the RC hobby for a few years now, but now I decided to step things up a bit and build a 'simple' single staged coilgun. The plan is to make a build log along the way and ask a LOT of questions. xD

So anyways, I'm thinking of running on 300-400 volts and using a 6-9 mm projectile. Not entirely sure about the projectile size yet, but that'll come along the way I guess. As many have used Uzzors 50W capacitor charger with great success, I decided to give it a go. I went to the dump and got me an old monitor from which I salvages a flyback transformer, but now I've got some questions about some components on the circuit.

First of all, what are these components (In the red circle)? They look somewhat diode-ish, but I can't find a detailed description of the parts. Also, Should I get eight of the same diodes for both sides of the transformer (Driver and rectifier), the RGP10J? Furthermore, I never wound a transformer before, only brushless motors, so I'm not sure how to make the primary coil. Bifilar? Centertapped? Google wasn't particularly helpful on this one... xP

So yeah, that's a lot of questions. Thanks in advance. ^^
Hanzie

1354984604 6534 FT0 Cfpr Capacitor Charger Part

Legit_bacon

Sat Dec 08 2012, 08:47PM

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

Firstly those diodey things are called zenar diodes, and no you don't need to put them on the other side of the transformer (its called a bridge rectifier)

Could I suggest you start with something simplier as you don't seem to have much experience, perhaps try Uzzors 15w boost converter? Much simpilier and comes with some tried and tested pbc designs.
sorry for all the mistakes I'm sure this is from my phone.

Ash Small

Sat Dec 08 2012, 09:08PM

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

Hanzie wrote ...

I'm not sure how to make the primary coil. Bifilar? Centertapped? Google wasn't particularly helpful on this one... xP

It's centre tapped. 14 turns, all in the same direction, with the tap in the middle (There is a note on the schematic saying 'centre tapped, 7+7')

Hanzie

Sat Dec 08 2012, 09:28PM

Registered Member #6534 Joined: Sat Sept 08 2012, 12:22PM
Location: The Netherlands
Posts: 32

Ah, they're zener diodes! I know about those, but the books I have here give them a different icon. Same goes for resistors for some reason, probably has something to do with European vs American icons. xD
I also know about the rectifier, those are the four RGP10J diodes. On the primary side however, the diodes used are only called 1A fast diodes so I'm wondering if they're of the same type (I would think that they are).
I made something similar to that boost converter once and it worked fine, but now I'm looking for a little more speed/efficiency on the charging process.
Right, so now the main problem would be winding the transformer itself. I should be able to figure that out. ^^
Thanks for the input!

Hanzie

Sat Dec 08 2012, 09:38PM

Registered Member #6534 Joined: Sat Sept 08 2012, 12:22PM
Location: The Netherlands
Posts: 32

Thanks Ash. The bifilar part got me a bit confused, but it seems to make sense now.
Thanks again!

Steve Conner

Sun Dec 09 2012, 11:35AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Yes, you can use the same diode everywhere. The UF4007 is another possibility.

The best way to wind the 7+7 turn primary is 7 turns bifilar, connect the end of wire 1 to the start of wire 2 to form the centre tap. It's not hugely important though. Two separate 7 turn windings would probably work fine.

When I built this circuit, I used the ferrite transformer from an ATX power supply. No rewinding was needed, the old 5V output winding became the primary, and the old primary became the secondary. The only issue was that the output voltage was a bit low, so I had to use a doubler instead of a bridge rectifier to charge 400V caps.

I was very pleased with the performance, it drew about 8A at 12V and charged caps pretty quick.

Hanzie

Fri Dec 14 2012, 08:13AM

Registered Member #6534 Joined: Sat Sept 08 2012, 12:22PM
Location: The Netherlands
Posts: 32

Right, someone at my RC-club said he should have some high voltage caps laying around. As far as I know him, it could be anything between 200 to a coupe of thousands of volts rated caps, so yeah, let's hope they're around the 300-400 V range... xD
I'll be at the club this evening, so we'll see what he comes up with.

Hanzie

Sun Dec 23 2012, 09:20PM

Registered Member #6534 Joined: Sat Sept 08 2012, 12:22PM
Location: The Netherlands
Posts: 32

Well, the big capacitor bank will probably have to wait at least another week as my fellow club-member hadn't been to his storage shed yet. He said he would go there somewhere this week though, so we'll see. ^^
In the meantime I've made a charging-circuit. As mouser's shipping costs were higher than the actual prize of the parts, I decided to make another circuit with parts I could salvage from the mountains of old electronics I have laying around. Another guy at my club helped designing a circuit, and this is what he came up with. It powers a flyback transformer with 14 on the primary and 240 on the secondary side, like the one in Uzzors project. I did a quick test running on a very empty lead-acid battery (about 9 volts, I know, I should recharge it xD) and I could get some +/- 1.5mm sparks from the secondary leads. Once I tried it with a fresh 12V lead battery the mosfet died, so I'll have to go look for a stronger one. Shouldn't be too hard, as I have like a ton already laying around here. I will measure and post its performance once I get it up and running again.
Hanzie

Hanzie

Fri Jan 25 2013, 04:40PM

Registered Member #6534 Joined: Sat Sept 08 2012, 12:22PM
Location: The Netherlands
Posts: 32

Still working on it. Charging circuit works fine, and I found some capacitors: http://www.ebay.com/itm/1000uF-450V-PCB-Caps-Dip-Componnt-Radial-Electrolytic-Capacitors-KMH-1PC-New-/281037415517?pt=LH_DefaultDomain_0&hash=item416f22a45d
Turns out he didn't have any after all, so I'm gonna go for these instead. What do you guys think?
(That's one big link btw...)

PSCG

Fri Jan 25 2013, 05:34PM

Registered Member #3792 Joined: Sun Mar 27 2011, 06:07PM
Location:
Posts: 136

I have bought 2 of these capacitors and they are good enough to power a simple coilgun with a projectile close to yours (7 mm diameter) and punch a hole to a aluminum can (using only 1 capacitor). Also, i believe MrFlatox uses the same capacitors to power his ETC accelerator so they are fine to use for a coilgun.

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