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Filter/smoothing Capacitor for cap bank charging circuit

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fullclip

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Ok guys this is my first post on this site and to be honest I'm bit of a noob and im still in high school so some patience would be appreciated
So I bought some pretty nice Caps I got 6 200 volt 1600 uF caps and I want to put them together in a cap bank I got the cap bank end worked out (for the most part) I been having trouble with the charging circuit tho What I been doing is putting 120 VAC thru a full wave rectifier I was suprised when my voltage out read only 109VDC so I think if I used a Cap I could achieve a higher steady voltage

Now what kind of cap would i need for such an application would it be best to take 2 electro caps and run the current threw there ? and if I were to do this how many uF am I looking for sorry if I'm a little vague with my description
 
First, it is potentially dangerous to use 120vac mains directly. Switching power supply isolate their output with a feedback control that is opto isolated. If you do this at least use the neutral side of plug (larger width plug blade) for ground which only works for half wave rectifier. This won't help if you are using a full wave bridge as the neutral side reverses on each cycle.

Now, 120vac will give you 170 vac peak. With a full wave bridge you will get 120 vdc rms minus the 1.3-1.6 volt drop from two conducting rectifiers in the bridge.

An infinite value cap will charge to peak of sinewave, 170 vdc - 1.5vdc for rectifies. Full wave peaks occur at 120 Hz rate so there are 8.333 msec gap per peak.

Capacitor discharge is dependent on current discharged. Current from cap is I = C dV/dt where dV is drop in voltage over time period dt.

If you want to draw 10 amps with no more then 3 vdc of ripple drop from 168.5 volts then you would need a cap value of 10 amps * 8.333 msec / 3 volts = 27,800 uF. If you do this at half wave the time gap goes to 16.6 msec and the cap value has to double to last twice the discharge gap time.
 
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Would I need to draw 10 amps? sounds like a bit much no? I'm charging 6 1600uF caps Couldn't I put a resistor between the cap bank and the charging circuit so that they charged a little slower? that way there would be less stress on the filter cap ? or would i need the resistor between the Rectifier and the filter cap?
 
You did not say what your load current requirement is. Adjust cap value and ripple requirement to meet your need.
 
well wouldnt the load current be equal to how much current the caps can hold? how would I find out the amount of current it takes to charge all 6 capacitors?
 
No, read the equation. The cap must support the load between the recharge peaks of the rectifier output.

If you must play with this, please put a fuse on AC side and only run it from a GFI outlet. I would hate to contribute to you hurting yourself. You can still kill yourself taking a 170 vdc discharge from that large of capacitance.
 
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I'm sorry I'm trying to follow you here I need to know what the load is when the capacitor bank is charging
 
it is running on a GFI outlet Whenever I handle the capacitors I wear electricians gloves and long sleeves I try to be pretty careful with them 1600 uF is quite a bit of charge at 170 volts
 
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The higher the value of the cap, the shorter the recharge period and the higher the peak current through the rectifiers. This is not of much concern as the rectifier dissipation is based on average current.

What is important is what your d.c. output load requirement is and how much voltage ripple your load can tolerate.
 
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well the capacitors are only discharging into a large coil so I don't see the need for the voltage to be real smooth I just wanted it smooth so I could get a higher voltage
I'm gonna go to bed and sleep on this do you mind if i messaged you some time for some help with my capacitor bank?
 
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