Introduction: Cheap/free Capacitor Bank and Charger

HOW TO: Make a capacitor bank useful for many applications, ie a railgun, coilgun, RFID zapper, for $0~50 depeneding on what tools you have and how fancy you want the final product.

**Now with solid state trigger**

Step 1: Gather Materials

I have modified the circuit to use a solid state trigger, an SCR. I used this one, number from digikey: S4020L-ND

400v, 20A so ~200A surge, less than $2

The pins are, from left to right: Anode; Cathode; Gate
The SCR is essentially a diode, so be sure to hook the negative of the caps to the cathode and the anode to one of the binding posts. The positive of the caps also goes to a binding post. When you put enough current (check the chip spec, only a few volts and ma IIRC) through the gate it is "closed", allowing current to flow through it in the right direction. It will stay "closed" until the current flow stops, IE the caps are completely drained. Then you can just solder up a switch to the positive lead from the battery holder to the gate, this way you will be able to discharge even when the switch is off. I will put a new schematic up soon.

I applied all this to a coil gun and will write it up soon. This is just and update for those who request a solid state switch.

Keep in mind that this is my first instructable, hell it's my first time wielding a soldering iron. Comments appreciated :D

The cheap way: (note that if you choose to go this way you should skip to step 4)
$0.00 (4) Disposable cameras You can get these for free used
$0.00 (X) Scraps of wire I used the wires from an old stereo system
$7.99 (1) Spool of solder (with soldering iron!)
$4.99* (1) Spool of 12 AWG wire.
$3.68* (1) Electrical tape

Assuming you already have everything but the 12AWG stuff, which you probably do, that's only $5. Hell, you could probably get away with paperclips if you were really trying to get it done cheap.

Required materials:
$0.00 (4) Disposable cameras You can get these for free used
$0.00 (X) Scraps of wire I used the wires from an old stereo system
$1.39 (1) LED holders (package of 2)
$1.49 (1) Green LED (package of 2)
$1.49 (1) Red LED (package of 2)
$3.00* (1) Toggle Switch
$1.49 (1) 2AA Battery Holder
$3.69 (1) Project Box
$4.99 (1) Binding Posts

Things you probably have but might not:
$7.99 (1) Spool of solder (with soldering iron!)
$4.99* (1) Spool of 12 AWG wire.
$3.68* (1) Electrical tape
*I just guessed the prices of *'ed items

I got all those parts at radio shack, expensive but that's what I pay for convienence.

Soldering Iron
Assorted drill bits

Note that I took the picture after I finished the project...

Step 2: Take Out the Camera Board

Alright, so take apart one of the cameras, and look at the top right of the back of the board. Hopefully it's an LED, but if it's not, just try the next camera. I got 5 Kodak cameras, two of them had LED boards.

Assuming you have an LED charging circuit, let's see the important parts. There are the battery contacts, +1.5v and ground, the LED out, ~+2.8v and ground, and the capacitor contacts, +480v and ground. We also want to get rid of the xenon bulb, it adds a lot of thickness.

So I started with the capacitor, heat it up with the soldering iron and pull it out. Then I went to the battery contacts, there is a ton of metal on one of them, just rip it off with pliers, apply heat on the other side and pull it out. The LED contacts are by far the hardest part, they are very close together. Finally, take off the plastic over the xenon flash bulb (not done in this picture), and desolder the bulb.

Step 3: The Box!

I bought a huge box, you could go much smaller if you wanted too. Drill holes for the LED holders, red and green, and a hole for the switch, and two holes for the binding posts. I was retarded and drilled through the supports, which isn't a big deal but it's harder to tighten the LED holders when they are half on a post and half off. Thankfully I realized this by the time I drilled the switch. Now drill two holes for the binding posts, and screw everything together.

Okay, now connect all the wires. Put ground from the battery directly to the farthest right pin of the switch. Put the ground of the green LED and the camera circuit on the middle pin of the switch. Put the +3v of the battery pack with the positive LED and camera circuit leads. Now flick the switch and the green LED should light up. If so, turn it off and continue, if not, check your circuit and connections, then stop because you have no f*cking idea what you did wrong(note that I did this about 3 times during this project).

Assuming you have the power hooked up properly, hook up the red LED (it can only go one way, so make sure to check before you solder) and connect the capacitor outputs with the binding posts. When you flick the switch this time, the red and green leds should light up. Hopefully they do, so take your multimeter and read the output of the binding posts, should be about 500v.

Alternatively if you are using the SCR, hook the anode (first pin) to the scr, the cathode (second pin) to a binding post, and the negative of the caps to a binding post. Then take a momentary switch and hook it to the SCR's gate (third pin) and to the positive lead of the battery holder, ensuring it has power ever when the main power switch is off. This way you can safely discharge the caps without having the charger on.

I wrapped the circuit board in electrical tape and velcro'ed it to the bottom of the box.

Step 4: Crappy Wanna-be Schematic

This poorly drawn schematic just might aid you in reading my poorly written instructions.

I don't know how to use Eagle, and I didn't feel like getting all the symbols, but I think the text will suffice. I think the image pretty much speaks for itself.

The break above the Power LED is the power switch

These are the battery contacts

These are the power led's contacts.

These are the status led's contacts.

These are the capacitor's contacts.

Step 5: The Actual Bank

Alright, now that we have a sweet charger in a cool looking box, let's get something to connect it to.

Remember all those disposable cameras? Pull the capacitors out, I got 4 caps rated at 330volts and 120µFarads. Make sure the gray stripes are all pointing in the same direction, and get out some of that 12AWG wire. As you can see in the picture, I stripped only part of the wire. To do this, make the circular cuts like you usually would, then take a razor blade and slice down the middle. Then just peel off the rubber, it's way easier than it sounds.

Now using a small screwdriver, push throught the copper strands making a slot the capacitor leads can go through. Put em through, and then solder, it's that simple. I reccomend making both wires first, then soldering all the caps onto one wire, and then the other wire. It's easier that way.

Step 6: We're Finished! Now What...

Now that you have a nice little capacitor bank, what are you to do with it?

I plan to build assorted small scale electromagnetic goodies, but it's up to you really. Here are some links you might find interesting, I know I did.

Micro railgun
Mini coil launcher
Lots of coilgun info

Well, that's all for now, once I build coil/rail guns I will post instructables for them :D

Thanks for reading, leave a comment :)


corax made it!(author)2006-10-27

It seems this relatively simple design would work for an emp generator experiment?

Derin made it!(author)2007-07-21

what is a emp generator?i know i am dumb

bilden made it!(author)2016-01-25

whoa this thread has been going for nine years!

ghost5ninja made it!(author)2016-11-09

dang thats crazy!

Greasefire made it!(author)2007-07-25

EMP is shorthand for "electromagnetic pulse". In Ocean's eleven, they used a generator the size of a van to knock out the casino's power grid (along with half the city's! ;])

firemanfu made it!(author)2007-10-25

you also get an emp from a nuke going off

alphapyr0 made it!(author)2011-06-13

not just any nuke it would have to be a ytterbium core HE rail nuke.

arizonadixon made it!(author)2011-06-22

this is not necessarily true, any nuclear weapon with sufishint gamma output that is detonated above ~15km will produce an EMP of significant power.

googleman made it!(author)2008-07-18

oceans is cool

TheDeviant13 made it!(author)2009-03-27

emp stands for "Electromagnetic-Pulse" EMP pulses can knock out electronics such as radios and will make crt TV's

freerunnin1 made it!(author)2010-08-27

doesn't an EMP destroy capacitors or something? therefore rendering electronic equipment useless or is it just temporary?

S33PlusPlus made it!(author)2011-04-17

I realize this is rather old, but EMP affects anything sensitive to sudden current spikes (i.e. semiconductors). Theoretically you *could* trash a capacitor with an induced current, but in reality all the transistors would explode far before a capacitor would catastrophically fail.

And @TheDeviant13: What do you mean "will make CRT TVs"? It will screw up the picture pretty bad, but that goes for all magnetic fields.

n3ldan made it!(author)2007-07-25

A little explanation to greasefire's response: Note that I am no expert on the subject; but I think I have a fairly accurate grasp on it. An electromagnetic pulse is a powerful magnetic field that, due to electromagnetic induction, creates a voltage differential between metal objects. For example, a large EMP near an RFID tag would create a voltage differential between different parts of the antenna, which could potentially fry the chip and or antenna.

blablabla123 made it!(author)2009-03-18

This would absolutely work, in fact, i made one work using the individual charger output

montdor1 made it!(author)2012-10-09

This EMP would, as enivisaged herein, work. Use it. Enough corporate spying, prying and lying.

bilden made it!(author)2016-01-25

pushing thru the cable like that is a nice way to go! Hmm maybe basic for some but I wonder what happens if I would gather Capacitors of different values. Lets say they are in some approximate same voltage rating.. Would they "complete each other" or would the smallest melt directly?

bilden made it!(author)2016-01-25

save the xenon lamps! I just built myself a xenon flash dirt cheap that now fits my grandpas TLR from 1950.

nutsandbolts_64 made it!(author)2010-12-27

If you pumped all of the power in the bank into a tiny tiny gauge wire, what would happen?

Robert+Powell made it!(author)2014-10-19

The wire would fry and/or make a huge spark and bang.

liddleLOL made it!(author)2011-09-30

I need help:

I am making a charging circuit for a coilgun, but i accidentally bought non polar caps. I was wondering if i could still use these with some sort of circuit adjustment, or if i need to purchase all new polarized caps? Can you help?

Robert+Powell made it!(author)2014-10-19

If you want to make a coilgun you need to have enough microarads, so if you want, you can use those with this circuit but you need to use those with another project, but yea, you need polarized caps. :-)

man2220 made it!(author)2012-05-04

I have this set up to two AA and 29 330 v capacitors ranging from 160 to 80 uf and the transistor keeps smoking and the board stops working giving me almost no charge can anyone help?

Robert+Powell made it!(author)2014-10-19

Whoa! no wonder it's smoking! That's WAY to many caps! You need to have about 8 boards in parallel to give enough amps.

GIBBERATOR made it!(author)2009-08-17

how powerful is this, or will it just make a weak coil gun?

Terafyde made it!(author)2014-09-12

The power of it depends on the amount of capacitors and the amount of energy they can store.

hopelost9 made it!(author)2013-07-22

so im kinda confused with the capacitors. do you treat the line of capcitors as one, and just attach the first one to the charger, and they will all charge? or something else?

%7ECableGuy made it!(author)2012-06-07

Is it possible to give more voltage to the Camera Circuit for faster charge?

soheil made it!(author)2012-06-02

Hmmm... I wasn't able to understand the "connecting the scr" part
What do you mean by attach the anode to the scr? do we attach the thing to itself?!

StartedBullet made it!(author)2011-06-30

Any idea where I can get these cameras free? Walmart will not give them away.

blueeyesseto made it!(author)2011-02-02

if anyone can get a large amount of these used disposable cameras say 50 i am willing to pay $10 for them seeing that your getting them for free and that should cover shipping

tulavatalo made it!(author)2009-04-06

the nuke creates a emp that krashes most elektronik devices in a raduis of 10km

dumle29 made it!(author)2009-09-19

a nuke would fry way more than stuff in 10 km radius

tulavatalo made it!(author)2009-09-20

it depends on the altitude of the detonation a nuke is often detonated about 500 m above ground but if you blow a nuke at 10km altitude it would take out eny not shilded electronics in an area the sise of usa

dumle29 made it!(author)2009-09-20


scottjones1998 made it!(author)2010-03-31

right before it blew you to pieces

Biscuitus made it!(author)2010-12-20

Actually no.

An EMP is generated from a nuclear device being detonated at altitude. It's also known as an "airburst" In the Cold War days it was thought that Soviet forces would lead a nuclear attack with a series of airbursts to knock out civilian infrastructure. The actual effects of the blast is not very great because they don't have to use a "city buster" (a device in the megaton range) to get the same effect, so the heat, blast and all of that wouldn't be as great because it's fairly high up (think miles).

How do I know this? I was in the military and it was my job to know.

OXI2vasyl made it!(author)2010-08-12

are u watched future weapons on discovery channel xD

tulavatalo made it!(author)2010-08-14


Coindude19 made it!(author)2010-11-29

I found some high-voltage capacators from old adapters to computers and video consules and one of them reads 400v and 68 uf

ARJOON made it!(author)2010-09-07

fake. Your circuit is a broken one. This ciruit dont work because there is no component on it. IF there was on the bottom it would be elevated but nice intructable maybe you replaced the circuit with a new one.

fundash made it!(author)2010-09-04

be carfull with this, those wires are pretty close!

bigpinecone made it!(author)2006-10-28


demonxkid made it!(author)2009-09-18

what is the best way to do this

bigpinecone made it!(author)2009-09-18

screwdriver on the leads.

demonxkid made it!(author)2009-09-20

like 1 screwdriver connecting the leads or just touch 1 then the other

bigpinecone made it!(author)2009-09-20

'cross the leads.

Punkguyta made it!(author)2010-04-06

 With your finger

freerunnin1 made it!(author)2010-08-27

lol id laugh if someone actually did that and kept trying like "for some reason my capacitors aren't discharging"

demonxkid made it!(author)2009-09-20

is how much it holds the v or uf on the side of the conductor

bigpinecone made it!(author)2009-09-21

uF is how much it can hold. stands for micro farads. V is the max voltage it will operate at.

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