Power Supply Filter Capacitor Size

[Harry Bissell]

Our term is "Ripple Current" its mostly important in things like switching power
supplies, motor drives, and other supplies that are very heavily loaded.
Probably will not be a DIY problem. But parallel caps is an excellent solution
and is how the problem is usually solved in "big current" devices...

:^) Harry (into big current devices here...) Bissell

Martin Czech wrote:

> It may appear that the filter cap should be as large as possible.  But in
> this case the trafo sees a very low load, ie. almost a short when the
> coil voltage rises.
>
> So, one has also to calculate the cap ac current, we say "Brummstrom"
> over here , "humm current?". Some caps get really hot due to those currents.
> It was one of my sins of youth to buy a cheap 10000uF cap for
> a 8V*10A trafo, yes the voltage rating was ok, but the ac current for 8A
> load was much too high, too much heat, had to change the circuit...
>
> There are special caps that allow for large ac currents, but maybe an
> array of cheaper and smaller caps will also be a solution. Of course,
> the trafo must be able to carry that peak current, too. Sometimes a
> current limiting resistor or a choke is used.
>
> There are formulas for this, but I don't remember now....
>
> m.c.