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 :)



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    278 Discussions


    12 years ago on Step 6

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

    14 replies

    Reply 11 years ago on Step 6

    what is a emp generator?i know i am dumb


    Reply 3 years ago

    whoa this thread has been going for nine years!


    Reply 11 years ago on Step 6

    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! ;])


    Reply 8 years ago on Introduction

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


    Reply 10 years ago on Introduction

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


    Reply 8 years ago on Step 6

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


    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.


    Reply 11 years ago on Step 6

    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.


    Reply 10 years ago on Step 6

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


    Reply 6 years ago on Introduction

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


    3 years ago

    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?


    3 years ago

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


    7 years ago on Introduction

    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?