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How to charge up a capacitor? Answered

I heard some website just use a transistor and transformer circuit to charge up a photo flasher cap.(May be high frequency output)
If so , can I charge up three or four capacitors with parallel or series circuit?

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Don't  Don't ....
D
o NOT mix capacitors of different voltages and capacities.
You can have a spectacularly dangerous failure.

Electrolytic capacitors have liquids similar to water inside and
the metal cans are a small pressure container.

When the cap is accidentally abused beyond its design parameters it can
in a matter of seconds begin to heat up and that liquid may turn to steam
which greatly increases the pressure and may become an explosive
grenade with burning gases and small sharp shrapnel projectiles .

A

To be clear, Photo Flash caps from disposable cameras often have the same capacity. I have only experienced an explosive discharge when I accidentally shorted one of the transistors on the charger board. A piece of plastic from the transistor hit my face at an uncomfortable speed.

Same capacity does not mean identical voltages which is the variable that can cause a cap to explode...

All you need is a power source connected to the leads of a capacitor to charge it. You can charge as many as you want in parallel.

http://www.talkingelectronics.com/projects/XenonFlasher/XenonFlasher.html
has some circuit diagrams for the charging of a photoflash capacitor, from a single AA battery. I think most of the circuits on this page were reverse-engineered from actual camera circuits found in the wild.

Obviously there is some sort of magic going on inside this charger circuit, since the input supply has a voltage of around 1.5 VDC, and an output voltage, across the big capacitor, of around 300 VDC.

For this kind of charger circuit, the maximum DC voltage it can produce is essentially fixed, Vmax,  some number around 300 to 400 VDC.  A consequence of this is the maximum amount of energy you can store in the big capacitor, depends only on the size (capacitance, in farads) of that big capacitor, since Umax = 0.5*C*(Vmax)^2
http://en.wikipedia.org/wiki/Capacitor#Energy_of_electric_field

Supposing the original big capacitor at the output was a 300 uF capacitor, rated at 350 VDC.  Putting two, or three,  of those in parallel at the output would give you an effective capacitance of 600 uF, or 900 uF, respectively.

One drawback to this trick of charging several big capacitors in parallel, on a charger intended for only one, is that it usually takes 2 times, or 3 times,  or n times as many seconds to charge  up this combined capacitance.  So with a large number of parallel capacitors, it can take an inconveniently long time to charge.

For capacitors in series, I don't think there is any advantage to be gained from putting several big electrolytic capacitors in series, with this kind of charger.  Putting capacitors in series makes their total capacitance smaller; e.g. (1/2), or (1/3), or (1/n), for 2,3, ...n capacitors that are all the same size. See also:
http://en.wikipedia.org/wiki/Series_and_parallel_circuits