Coilgun design - Page 1
Forum section: electronics / projects

author: Analogtech
author_rank: Contributor
timestamp: February 12, 2013, 09:35:15 pm
content: Hello everyone,this is my first post on the eevblog forum. I am currently designing a coilgun (if you don't know what that is,google it) and would like some assistance. I am hopeless at any form of schematic capture program so if anyone could please make me a kicad file for the attached schematic and also a pcb layout if possible i would be extremely grateful.i would also like to implement such features like MOSFET and battery temperate (preferably using a thermocouple) and battery and capacitor voltage and duty cycle measurement readouts on an lcd screen (of the type used in old monochrome nokia phones) using a PIC (the pic is used only for the lcd and measurements and not actually for the boost signal) if anyone could do this for me i would be exceedingly grateful.

author: AndyC_772
author_rank: Super Contributor
timestamp: February 12, 2013, 10:28:30 pm
content: Erm... you're 14 years old and you want someone to spend a couple of weeks designing you a 600V coil gun? Yikes.

author: houdini
author_rank: Regular Contributor
timestamp: February 13, 2013, 03:35:44 am
content: 4hv.org would be a better place to look. There are alot of people who build large coil guns and such there.

author: smashedProton
author_rank: Frequent Contributor
timestamp: February 13, 2013, 05:21:43 am
content: Just a social pointer for you. Never ask someone you dont know to do something for you. I can give you a kicad library if you send me your email

author: EEVblog
author_rank: Unknown
timestamp: February 13, 2013, 09:19:57 am
content: Try googling open source coil gun or some such, likely a circuit and board already done, or even a kit.No one is going to lay out a board for you!Sent from my Nexus 7 using Tapatalk 2

author: poorchava
author_rank: Super Contributor
timestamp: February 13, 2013, 03:37:59 pm
content: Which part of the coilgun are you actually designing? Since you want someone to make schematic and pcb layout, what's left? (Assuming that this is a single-stage coilgun, because multistage needs some mechanical engineering to work). DIY stands for do-it-yourself no find-someone-who-does-it-for-you.First: stop using Kicad - pcb/sch design won't seem that hard anymore. Go for Diptrace free version. Best ratio of capabilities to priceYou already have a boost converter schematic, so main part is done. Readout on LCD is easy to do because because there many code libraries for Nokia LCDs. Voltage measurement is easy: you just need a voltage divider and input protection on the MCU (google that). Temperature measurement is also easy, but using integrated sensors like LM35 or DS18B12. Actually I think DS18B20 would be better because of interference from the converter. this sensor has 1-wire digital interface and also many software examples are available on the net.

author: smashedProton
author_rank: Frequent Contributor
timestamp: February 13, 2013, 06:26:50 pm
content: Just use arduino, Christ. your fourteen so education is all that matters. No need to make it designed for manufacturer

author: vk2fro
author_rank: Newbie
timestamp: February 14, 2013, 03:29:33 am
content: I'm new here - but at age 14 I was playing with lasers, high voltages, and rf (radios; CB back then - and was a little naughty with an amplifier). BUT.MAKE NO MISTAKE OP! the capacitors in a 600v railgun/coilgun will kill you no questions asked. A large bank of caps like mine (900v, 2.45kJ) is easily10 timesas powerul as the machine used to restart your heart in the hospital (a defibillator).This is my bank - its far from finished - the controller (hand control) is on the workbench out of camera view. On the left far is the charger, the ultra efficient ZVS driver with home wound tramsformer, based on the core from a TV flyback (left, far rear), some house wire scrounged from a PC cord) and #24 guage ECW. Winding 700 turns of that stuff is not an enjoyable pastime. In front is the pair of mosfets and their sundry components. Notice the tiny heatsinks? Very very little heat is generated; yet this guy can charge up this big bank in under a minute. Front stage left is the bleeder resistor; which fails safe (using the open set of relay contacts to allow the caps to charge, NC set puts the resistor across). So if I loose all power to it, the system will be in a fail safe condition within 3 minutes.Note that its a right mess at the moment as I havent worked on it for a little while - caps are definatly dead 0 v as they have had a clip lead across them for the last month which I removed to double check with the DMM. Presently its wired in parallel configuration, for 450V 24mF (milliFarad), but once my bits arrive from element14 I'll be rewiring it series configuration for 900V 12mF. Heavy guage wiring is a must - this thing I reckon dumps in excess of 1000A when it dischargesCapacitor banks are great fun to play with, but dont be silly with them - they are stupidly dangerous as well. You can easily kill yourself with one (did I already mention this?), ruin your hearing, bugger your eyesight and stuff life in general if you make a mistake. I'm sure the bank pictured above is capable of blowing off a digit so I wear saftey gloves when handling it, and have a set of earmuffs and saftey glasses.Definatly go the arduino as suggested - they make doing uC projects for an absolute noob to uC's like me pretty easy.Now a quick threadjack (sorry OP) where can I get a box to house this thing - its 56 long by 30 wide by 27 high (cm). I'll need extra length or width to stuff in the electronics, arduino and the batteries (a pair of 12V 7Ah gels).Oh and yes at 14 I did want a death ray (Well a laser that can burn stuff). I now have that wish (3 watts of white light!). Lasers too are fun, but like the cap bank, easy to ruin your life with. Mine is housed along with some $600 galvo's and a controller - I built myself a computer controlled laser show. Burning stuff with the 3 lasers inside it got boring really quickFor the record I'm 37, am an advanced amateur radio operator (ham to some) and treat RF, HV and laser light with the respect it deserves - lots LOL!

author: notsob
author_rank: Frequent Contributor
timestamp: February 14, 2013, 04:28:30 am
content: You can probably get a box that size at the undertaker's - & the great advantage is it has a dual role, in case you accidentally touch the wrong wire

author: smashedProton
author_rank: Frequent Contributor
timestamp: February 14, 2013, 05:11:43 am
content: I have made my coilgun with a single 400v 370uf electrolytic. Looking back, I'm lucky to be alive. I would discourage you to make a coilgun. Make a stun gun instead. Much more practical

author: IanB
author_rank: Super Contributor
timestamp: February 14, 2013, 06:10:23 am
content: Quote from: vk2fro on February 14, 2013, 03:29:33 amOn the subject of accidental discharges, I was once experimenting with the flash circuit from one of those cheap disposable cameras. For some reason the flash wouldn't fire and I was prodding around, looking for a loose connection or something. Suddenly the capacitor discharged across a faulty connection on the PCB, bypassing the flash tube and dumping all its energy into the short. Well anyway the bang was so loud it made my ears sing and I practically jumped out of my seat. And that was with a baby capacitor...

author: AndyC_772
author_rank: Super Contributor
timestamp: February 14, 2013, 09:24:34 am
content: I had a similar experience with a photo flash capacitor, though it was induced with a screwdriver rather than a PCB short. Normally I prefer to learn from other peoples' mistakes rather than my own, but that flash and bang are the reason why I'm now so careful around any kind of high energy circuit. I'm sure it's no coincidence that I also still have a full complement of fingers and eyebrows.

author: GK
author_rank: Super Contributor
timestamp: February 14, 2013, 12:20:23 pm
content: Kiddies toys.Go to my CTM2K webpage(http://www.users.on.net/~glenk/ctm2k/ctm2k.htm), schematics section and download the PSU schematic. It shows 3 normally closed switches shorting the +3000V plate supply for the four 4CX1000A's to ground. This is not a drafting error. These are the safety switches/contacts on the three removable inspection/access panels (one at the lower front and two at the rear). A primitive but effective crowbar. It's not a good idea to remove any of the panels with the HT powered on unless you have a spare pair of underwear!BTW, does anyone know what to do with a collection of PCB-containing capacitors? Slowly upgrading all of my TX's to modern HV electrolytic caps (in series/parallel combinations with parallel R's for the kV stuff) and am accumulating a bit of a collection. I rang the EPA and they just palmed me off to a recycling mob that is confused and refused to take anything that doesn't look like either a CRT monitor or a DVD player!

author: SeanB
author_rank: Super Contributor
timestamp: February 14, 2013, 04:00:49 pm
content: Wrap in a triple layer of plastic, place in cardboard box and tape tight. Send sea mail to China via a eWaste bin at the local superstore.Here, place in bin and it disappears like magic on collection day.

author: vk2fro
author_rank: Newbie
timestamp: February 15, 2013, 12:22:54 am
content: Quote from: IanB on February 14, 2013, 06:10:23 amYes have done that before with a photo flash - it sounds like a firecracker going off. The amount of energy contained in a single (good) photo flash cap will throw you across the room. They sure pack a wallop. I too have experimented with them. Packed one up in a zippy case with two prods on it (ala cattle prodder/stun gun) and hit the right kind of steel/zinc pipe and it makes one hell of a bang, and thats just a 680uf flash capacitor. They are designed for this though; they need to dump as much energy as possible (up to the xenon tubes rating) as quickly as possible to get the bright flash we are all familiar with. Over speccing the cap to the tube doesnt result in a brighter flash; in fact it can shatter the tubeDead shorting capacitors not designed for it can damage the capacitor. Most common garden variety electrolytic caps are not designed to be hard shorted. Only "pulse" or "photo strobe" rated ones will tolerate repeated discharges of this kind.Quote from: notsob on February 14, 2013, 04:28:30 amThis both isnt funny, and is of no help. I dont go anywhere near my cap bank unless its fully discharged. The fact that I have already warned the OP twice about the dangers of these things should indicate that I am sensible when playing with such a powerful device. And to add its final design is to fail safe on 2 points; once a box is procured the lid will be interlocked so when the cabinet is unlocked, it starts the discharge process through the resistor. At the same time the arduino is told "sorry, cabinet unlocked" and thus cannot fire up the charger (ZVS). Once an LED is lit (bank in discharged state LED), the lid is safe to open. At the same time, the "bank hot" led will go out. Along with box metereage, only the stupid would open the lid while the meter still read any voltage above zero. Somebody mentioned they still had all their digits - so do I - even with HV gloves on I wont handle my bank or work on it while there is a charge in it. Even with the unit in failsafe, I'll still clip a lead across after checking with a multimeter!

author: Analogtech
author_rank: Contributor
timestamp: February 19, 2013, 06:16:12 pm
content: Thanks for all the warnings and yes,i do understand all safety precautions and ive also finished the schematics only the software and pcb layout remains and the setup looks good i might post pics if time allows me to here are the specs for the coilgunCharge time@ 24v 10a for a 500j bank : 3 secondsApprox velocity of slug (need to fine tune the coil) : 23 m/sNumber of shots per 2 12v lead acid batteries in series. : approx 78Penetration distance in jello (poor mans ballistic gel) : 1.2 cmWeight of entire gun :4.0 kg (including shielding)Also why does the waveform of the signal at the mosfets drain get a spike after every shot (i do have HV flyback diodes)