Pretty cool alternative to modular PSU's

[2uantuM]

moving the plates farther apart or making them larger

That will change the capacitance, not neccessarily make them hold the charge for a longer period of time. The other stuff you said was for the most part true.

On another note, capacitors can actually gain charge over time by picking up free electrons from the air. Even if a capacitor has been sitting on a shelf for a long period of time, it is always a good idea to discharge the capacitor by shorting it.

And no, a 9V battery wont make it hold 9V worth of "energy". The amount of energy it stores is dependent on its capacitance as well as the voltage (u=1/2cv^2) . You can have plates 3 miles apart with a 9V potential difference and have it store more energy than having the plates 2 millimeters apart (granted the plates would have to be pretty damn big). That said, don't base the energy contained in a capacitor on the voltage alone.

A capacitor on a power supply is usually packed with a paper insulator betweent he plates

Ehhh, its more of a grease kind of crap. Open up a capacitor one day, it's pretty cool .

 

[Moose777]

That will change the capacitance, not neccessarily make them hold the charge for a longer period of time. The other stuff you said was for the most part true.

On another note, capacitors can actually gain charge over time by picking up free electrons from the air. Even if a capacitor has been sitting on a shelf for a long period of time, it is always a good idea to discharge the capacitor by shorting it.

And no, a 9V battery wont make it hold 9V worth of "energy". The amount of energy it stores is dependent on its capacitance as well as the voltage (u=1/2cv^2) . You can have plates 3 miles apart with a 9V potential difference and have it store more energy than having the plates 2 millimeters apart (granted the plates would have to be pretty damn big). That said, don't base the energy contained in a capacitor on the voltage alone.



Ehhh, its more of a grease kind of crap. Open up a capacitor one day, it's pretty cool .

Thanks. I knew some of my info was off a bit. It's been a while since I've seriously done any kind of electronic stuff. I used to be in the telecommunications field (fire alarm side) and have worked on a lot of fire panels with capacitors and power supplies and we've never run into thing where something shorted out because a cap discharged after the power was cut for 15 minutes.

And it's a paper soaked in oil or a dialectric solution of sorts. I had one boil on me one day. And last night I got shocked pretty good with a disposable camera when I touched the board. That cap discharged into my hand. lol

Oh and the odds of it actually picking up a free electron is pretty rare. I actually found a box of old caps in my basement the other day that have been sitting there for 20+ years and I accidentally dropped one (glass) and it shattered and there was no "electrical" discharge of any sort just a glass discharge when it broke.

 

[2uantuM]

I've seen caps pick up charge from the air, enough to give you a little spark (feels like static if you get hit by it). I dont know if anyone has gotten a serious spark from it, but I suppose its possible.

I'm studying to be an Electrical & Computer Engineer, so I better know some of this stuff so I dont fry any of your cpus 20 years down the road

 

[Moose777]

I'm sure it's possible, I wasn't doubting that. I was just basically saying that the conditions would have to be absolutely perfect in order for it to pick up any type of loose or free electron.

I'm sure it's happened before but it was more than likely an isolated incident. And if not, it's probably pretty rare either way.

 

[bob]

Uhh, are you insane? the amount of charge delivered to your from those caps at 110V is probably enough to injur you.

My beastly power supply had 2 320v 1500uF capacitors in parellel. Made quite a band when I discharged them. Blew off the end of my small screwdriver.

Capacitors can pick up quite a charge from air and clothes. I was packing a 9" CRT to the garbage during the wintertime. about -5F outside. I had already discharged the CRT (wich is a good high voltage capacitor) and was walking out across my lawn to the garbage. I cant tell you how many times that thing bit me, it would build up quite a charge from my coat, then snap me on my wrists.

Like Ive said. You do not need to remove the power supply board. Keep your paws out of there, just clip the wires where they come out of the power supply and solder on a modular connector. Its simple, and much safer. You wont need to touch any dangerous peices that way. Its still dangerous, but less likley for someone to come into contact.