Help with caps for mini coilgun?

[Switch]

Ok so I had an old camera flash with a smaller cap that didn't say anything.I added another one(parallel) I had from another camera ,this one reads 330V 200uF, and that worked well.Now I have another two 200V 470 caps that I plan on adding in parallel for more power(and probably longer charge time). Is this a good idea?Are the values close enough? :-/

 

[Razako]

It should work fine as long as your input voltage doesn't exceed the values on any of the caps. I have a 200V 15,000 uf cap and two 25,000 uf 30 volt caps that I have connected in parallel powered by a 24 volt dc power supply. Great if you want a massive current surge.

 

[Switch]

I don't think the my circuit has over 200V.I'll just try it and see what happens....I hope nothing gets fried when I discharge them.

I also have three 100V 10,000 uF caps for a bigger coilgun when I'm gonna have time for it.What do you do with your setup?

 

[Switch]

Well I did it, but now the LED ont light anymore, not even after a few minutes of charging.It clearly has more power now, it cleared a hole through one side of a cigarette pack with a rather dull projectile a couple of times but that was it.It only makes a small mark now, and the charging high pitch whine is quieter now......I can't belive it sucked all the power from my fresh out of the charger Ni-MH's that fast.... :-/

 

[likewhat]

If you know what the capacitance is and also the charge voltage then it is pretty easy to find out how fast they will drain your batteries (assuming you know the mAh rating of the batteries).

Energy stored in a capacitor is 1/2*C*V^2 = 1/2*V*Q, where Q is the charge in coulombs V is the voltage and C is the capacitance.

For fun if you measure the speed of the thing you are shooting you can see how efficiently you are turning the stored potential energy in the capacitor into kinetic energy of the thing you are shooting, but maybe that is just me.

 

[Switch]

So how do I obtain Q?

Anyway, I got it to charge properly again and made a hole through it again but at the same time one of the wires connected to my switch exploded, the insulation turned to smoke...I don't know if this discharge was more powerful than the others or if it got weaker where I soldered it, but these wires are definetly to thin for this kind of power.I'll check if anything on the PCB got fried in the morning, and if it's ok, I'm gonna put some thicker wires and keep testing.

The projectile definetly has more kinetic energy than the average airsoft gun, but it lacks speed cause it's so heavy and that makes it kinda sucky over a distance or at piercing stuff.Sure hurt when I shot my own hand lol

Could it be that because the wires are too thin, they put up too much resistance and don't allow for an fast , efficient cap discharge?What do you think? :-/

 

[likewhat]

well to obtain Q, the stored charge you do algebra because you know V and C. When you discharge capacitors into a short it is pretty easy to have 100s or 1000s of Amps of current flowing, that is probably why you are melting stuff.

 

[rkcstr]

I have a couple 450VDC 3700uf capacitors, they're about the size of a Campbell's Chunky soup can each. I'm sure those would make a nice spark.

Also have some 40V caps of 13000, 25000, and 51000uf. Also huge.

They all have screw terminals, so you can hook up heavy gauge wire easily too.

I could be convinced to let go of them, if you're interested

 

[Things]

PLEASE be VERY careful, even though that tiny flash circuit looks harmless, when you add in capacitors things get a whole lot worse. Make sure you are GROUNDED when playing around with them, possibly add a bleeder resistor. Those caps have plenty of power to kill you if used incorrectly. On the lighter side, Coilguns are pretty fun little things, i hope you get yours working well.

 

[Razako]

PLEASE be VERY careful, even though that tiny flash circuit looks harmless, when you add in capacitors things get a whole lot worse. Make sure you are GROUNDED when playing around with them, possibly add a bleeder resistor. Those caps have plenty of power to kill you if used incorrectly. On the lighter side, Coilguns are pretty fun little things, i hope you get yours working well.

I only charge my caps up to 24V. At that voltage you can mess around with them all you want without worrying about getting shocked.

 

[Switch]

Well I'm not grounded, but I am very carefull around them, I'd hate to get shocked, whenever some wire gets disconected and can't discharge them I just short them with a screwdriver or some other metal thingy.I have no idea how high I'm charging them.... :-/ How would the bleeder resistor work?Would it drain the charge slowly?Where do I add it, and what value would work well for my setup?
Btw , I changed my thin wires and decided to leave only the 470uF caps on and for some reason it's charging fast and it's more powerfull than ever.I'm pretty happy with how it performs now so all I have to do now is figure some kind of pistol design for it

 

[likewhat]

If you just put a resistor to ground from the capacitor it will bleed down the voltage so they wont stay charged. The voltage bleed of time will be R*C, so you can use that equation and the time you want it to take, (1 min, 5 min, 10 sec...) and do time/capacitance to get what resistor you should use.

For example

30 seconds/ (2*470e-6 Farads) = ~ 30kohms

So you can just pick how long you want the charge to stay on the capacitors and then pick an appropriate resistor. The time it takes for the charge to reach 1 percent of its initial value is ~5RC.

 

[charleytown55il]

i have been shocked by a camera cap before. . . its not fun. my whole left forearm went numb. i was just taking apart the camera and it happened to be charged. end of story.

 

[Switch]

i have been shocked by a camera cap before. . . its not fun. my whole left forearm went numb. i was just taking apart the camera and it happened to be charged. end of story.

That sucks....I have to say I never got shocked by those and don't plan on getting to

I have another question: If I add another 2 of those 470uF caps, is my small camera SCR gonna be able to take the discharge? :-/ I don't wanna fry it , but I do wanna make the thing more powerfull...

 

[glona]

hi have a few old dis camers how do i go aboguht makeing a coil gun?

 

[Switch]

Strange....It's more powerfull with one 200V 820uF cap than with two of them in parallel....wtf? :-/
I pretty much suck at electronics so ...I would guess it's eighter that they have bigger capacitance and the discharge pulse is longer, creating a suckback effect on my projectile OR they're not charging enough.So how do I measure the voltage to which they're charged? Just put the voltmeter in paralel with the caps? Or would that be a bad idea? :-/

I also wann ask, if anyone would know, is the wire thickness gonna matter or it's just supposed to be thick enough not to melt from the high current?