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Iniaes

Fri Nov 14 2008, 08:54PM

Registered Member #1700 Joined: Tue Sept 16 2008, 06:06PM
Location: Bournemouth
Posts: 10

Hey guys, I have been playing with the idea of building a coilgun for the last few months, and now I have 7 weeks off, I though I would give it a go. The reasons are 2 fold, one, because it looks like something interesting to do, and 2, to teach myself about this sort of thing. My knowledge base is limited (GCSE level), and a little bit here and there from on the job, as I am a junior weapons engineer in the Royal Navy; which roughly equates to a walking tool bag/rag for mopping up with.

I was looking at building a "small" 2 or 3 stage coil gun, using IGBT to cut off coil supplies from capacitors to reduce attraction of the projectile after it has passed through the coil (edit: would the winding down from the blocking diode/bleeding resistor still cause this?), probably triggered by optical trip gates.

I understand using diodes between capacitor terminals to protect from back emf, or a rectifier to recycle the back emf (edit: can you change the polarity of a DC pulse?), as well as to protect the power supply that charges the capacitors (edit: found blocking diodes, what relationship between these and capacitors/coils is there?). I am currently studying semi conductor theory, as well as things like generators, AC/DC into a greater depth, as I am waiting to start my promotional course.

What I really would appreciate is how things like coil form wire gauges, and capacitor/diode statistics relate to charging and power sources, and discharge properties, ie what is a usefull output and what isn't, or what diode i should use and where. I have been looking at Electrolytic capacitors between 2000-5000 uf and using 0.1m Enamelled copper winding wire,class H (?).

Also, I was looking at buying fluke test equipment, any reccomendations would be very much appreciated. On to the coil gun links now that i see everywhere.

Thanks in advance.

Gratitude

Fri Nov 14 2008, 10:03PM

Registered Member #1702 Joined: Wed Sept 17 2008, 10:14PM
Location: Ukraine, Kiev
Posts: 33

actually for the begining you can take some disposal camera which they would have flash the reason is because they are using Electrolytic cap for discharging them into flash, take some disposal camera, but i'm sure you can buy them with very cheap and good price
try to remove and open one of them circuit cause you need just one circuit to charge the capacitors and you can use the capacitors of remaining circuit and connect them parallel to each other into that circuit.
and connect the coil instead of camera's flash
try to bring some AA or AAA baterry to charge the capacitors and that set, when your capacitors are fully charged then you have to discharge them into coil instead of flash :D

this is just for the begining, and if you want you can use Uzzorsz boost converter schematic diagram to make one for your self as i have done for my self

becareful about Electrolytic caps cause they are so finicky devices. but you need to make the high joule energy to have good electromagnetic flow in the coil even your coil must be good which there is some dependencies

if you need any help, i'm here for the while

Iniaes

Fri Nov 14 2008, 10:13PM

Registered Member #1700 Joined: Tue Sept 16 2008, 06:06PM
Location: Bournemouth
Posts: 10

Thankyou for the information Gratitude, from what you said, I can charge a 200V cap from a 12 volt battery correct? I know that a capacitors current discharge is inversely (?) proportional to the load across its terminals, hence their use as smoothing on waveform rectifiers. And as far a cheap components go, I have e-bay :D, and I know you can get very different properties linking capacitors in parrallel/series, but I don't know how the properties change with the setup, I think this is what you ares suggesting in the second part of your post.

Camel

Sat Nov 15 2008, 02:04AM

Registered Member #1694 Joined: Sat Sept 13 2008, 09:13AM
Location: Australia
Posts: 108

If you have two identical capacitors in series, the voltage rating doubles and the capacitance halves.
Two identical capacitors in parallel will double the capacitance.

rp181

Sat Nov 15 2008, 02:28AM

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

For charging, a voltage multiplier is very simple, can be run off mains voltage, and cam be as high as you want it. If your using SCR's, you are gonna have to current limit it to prevent di/dt failure.

Everything kind of depends on how much energy. What voltage? For beginner w/ expirience in electronics, ide suggest 100J. Easy enough to work with with a decent power.

At theese low power, you can use basically anything as a coilform. Pen tubes are simple and ever so cheap, and will work fine.

You can switch DC polarity with a inverter like setup, but you can try a V-Switch. This recycles the inductive energy back into the capacitors. This needs 2 IGBT's a stage.

Iniaes

Sat Nov 15 2008, 11:11AM

Registered Member #1700 Joined: Tue Sept 16 2008, 06:06PM
Location: Bournemouth
Posts: 10

I was almost the proud owner of a BIG (about 50 kilos) variac power supply, unfortunately the fun piloce came and stopped me from running off with it >,< I was looking at buying a voltage multiplyer, or building a cascade multiplyer and sitting it in some silicone oil.

For tubes I was looking at a nce small piece of PVC or acrylic, I,m looking at keeping the bore to less than 5mm at the moment, hoping to get hold of some silicone steel projectiles from a friend at University.

Also I'll look into the V-Switches, thanks guys.

Iniaes

Sun Nov 16 2008, 01:52PM

Registered Member #1700 Joined: Tue Sept 16 2008, 06:06PM
Location: Bournemouth
Posts: 10

I am currently looking at 0.75 uf 1000V IGBT Snubbers, and also some siemens 100A 1200V dual IGBT modules for power control; and some 6800uf 50V elecrolytic capacitors for power, however, I can't see the eri or ers(?) on the information page. And I'm still looking at that 0.1mm coppper wire for my coil forms.

As far as the barrel goes, I'm looking at a nice narrow plastic tube at the moment, I doubt that strength is going to be that big a problem at the scales I am working at for now, looking at using cpu fans to cool the coils, but I have doubts this is neccessary on wire with such a low volume to surface area ratio, seeing as copper conducts/radiates heat well.

Iniaes

Sun Nov 16 2008, 08:36PM

Registered Member #1700 Joined: Tue Sept 16 2008, 06:06PM
Location: Bournemouth
Posts: 10

Just found this page, probably all over this site, learnt tonnes today, I hope to have some circuit diagrams up before the end of the week, as well as some stats for the coils, projectiles and decided on the capacitor and primary power source for the capacitor banks.

Iniaes

Mon Nov 17 2008, 03:38PM

Registered Member #1700 Joined: Tue Sept 16 2008, 06:06PM
Location: Bournemouth
Posts: 10

Hey guys, been looking round, looking at running my coils from series Caps ran from 50V home round ferrite core Transformers, ran through a home made full wave rectifier (was making those back at school, so just a little to rememeber) still looking at control, probably going to use either opical trip gates or more likely, sensor coils. Been looking at different coil forms on Barry's coi gun site coil sim app.

Getting some nice big inductance figures, just need to get the rest of the circuit balanced, as well as the rest of the cmponents. Still looking at using IGBTs as control for the coil supply, although i'm still not sure if this will have and effect on the ringing effect. Any tips on using IGBTs are appreciated, as well as any toher general tips.

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