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Use a computer power supply to power a coil gun?

The summer bored-ness has finally kicked in, and I would like to build a coil gun. The usual idea is just to charge some capacitors, and then discharge then into a coil, but it is possible to use the 3.3v rail (or any rail) of a standard computer power supply to power a coil gun? The goal to have rapid fire ability (which is hard to accomplish with capacitors due to charge time), and not use a transformer (because I am to cheap to go and buy a decent one from Radioshack, or any other store)

understand that the pulse sent through the coil gun is something like 50-1000A at 200-500V so yeah, not gonna happen.

iv never tried this but i think the idea might work.. get a computer psu and locate the two huge capacitors in the cornner of the borad(there for filtering purposes) then get a switch or whatever rapide fire system u what to use like a 555 circut? because its uses main ac to charge it it will charge really fast.. might work maybe try it and tell we what happens... just be safe :)
ac-dc7 years ago
Radio Shack does not sell high current transformers you would need for rapid charge time.

Yes  you can use a computer PSU IF the peak voltage you need for your coil gun is the same as one of the PSU rails.  You will need to do a few things to make it work however.

1)  PSU regulates based on weighting of the voltage on one rail (usually, there are also more unique designs but I am considering the most common PC PSU designs).  You need to place a load on that rail so it  regulates properly enough that the PSU doesn't invoke its safety shutdown circuit.  How much of a load depends on your capacitor charging current and some experimentation may be needed, progressively increasing the load.  Also keep in mind that this load, for example if it is on 5V rail and you are charging caps from the 3.3 V rail, means you reduce the amount of current capacity on 3.3V rail since its current is  often taken from the 5V rail.

2)  You cannot hook a huge bank of capacitors directly to the PSU output, because it will drag the voltage down too low when you turn on the PSU or after each coil gun discharge, causing the PSU to drop out of regulation and turn off.  Instead you will need to put a low-ohm (perhaps 10 ohm or less) power resistor in series with the capacitor bank to slow down charging enough that the PSU stays running.

Exact values of capacitor bank, current, resistor, etc, cannot be answered until you determine the specifics of the project, the PSU you use, its tolerances, etc... all the other variables in the project are more fixed so you have to use them to get working values for the circuit you use to power it.

Ultimately I feel for someone new to doing it, it will be far easier, faster, to use a regular power transformer and bridge rectifier diodes to charge the capacitor bank instead of a switching PSU, though of course the PSU may then be larger.  Check surplus electronics websites for good deals on transformers, you will find them in far larger sizes and lower prices (even after having to pay shipping) than regular retail sale sources for electrical parts... or of course check eBay and other auction 'sites.