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Charge Capacitor Bank

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bd13

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In my efforts to make a coil gun i decided to use photoflash camera capacitors for my capacitor back for 2 reasons: 1) they are rated at 330v (and 80uf-160uf), and 2) they are FREE. I also decided to use one of the charging circuits from a camera to charge my 1360uf 330v capacitor bank made of 12 capacitors. there is a problem though, the bank takes about 2 minutes to charge upto 260v and generally goes VERY slow after that (when the circuit outputs ~330v). the camera circuit is supposed to take a 1.5v battery and convert it to 330vdc, so i went out and bought a 1.5v 700ma wall adapter to save batteries (and hopfully increase charge time) but that didn't work. so what i'm asking is if anyone has any plans for a schematic that will take in 120vac (wall current) and output ~330vdc. i tried a google search and it turned up nada, and i haven't really had much luck w/ transformer.....anything. but given the plans and part i can sure as hell build it. thanks
 
A Simple Voltage Doubler circuit will work.

PUT Put in a CURRENT LIMITING RESISTOR for protection.
This will help Prevent a HIGH Imput Surge Current when the caps start to charge from a full discharge
 
chemelec said:
A Simple Voltage Doubler circuit will work.

PUT Put in a CURRENT LIMITING RESISTOR for protection.
This will help Prevent a HIGH Imput Surge Current when the caps start to charge from a full discharge

Current limiting is hardly the problem. A doubler will peak out at 339v with a 120V input, and the actual line voltage may be higher at times. Needs a high voltage shutoff.
 
u probably already know this, but if u try to charge the capacitors with an AC signal, they WILL NOT charge cuz capacitors pass AC signals. it sounds like maybe thats wut is hapening w/ ur transformer??? it must b DC
 
Here is a simple doubler from 120VAC. The caps may be your capacitor bank split in half so each cap will only have 1/2 of the 339v across it. R1 limits the inrush current so not to blow the diodes. A low wattage 120VAC bulb (25w) or so could also be used here. The 220k charge balance resistors are optional if you find that the voltage is not balanced evenly over the 2 banks due to one bank having higher leakage current.

ALWAYS BE CAREFUL WHEN WORKING WITH MAINS!
 

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TheOne said:
ALWAYS BE CAREFUL WHEN WORKING WITH MAINS!
An isolation transformer might be a good idea here... :shock:
JB
 
zachtheterrible said:
u probably already know this, but if u try to charge the capacitors with an AC signal, they WILL NOT charge cuz capacitors pass AC signals. it sounds like maybe thats wut is hapening w/ ur transformer??? it must b DC

What will happen is that the caps will be like a short circuit (without using series limiting resistor) and heat up because of the internal resistance and blow up. :shock:

This is one reason large electrolytic caps have a ripple current rating when dealing with PSU's and SMPS's. The ripple current acts like an AC current through the cap, heating it up.
 
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