I am trying to build a extremely small charger unit out of a Vicor rectifier front end and a 375v to 48v converter module. I am doing homework in trying to figure out the required hold up capacitance in the system but am having issues knowing if I am going to be overloading my capacitors.

What I know:

I can have as much as 43db of ripple going into the converter which equates 89 V p-p. I would prefer around 31 or so V p-p and using Vicor's calculator that meets the capacitance shown in their data sheets.

So I end up with 200v 700uf. The units I am seeing on digikey have either a ripple current rating or ESR. The ones I was considering were a ripple of 3.1 amps but didn't give an ESR (would run 2x or 3x of these units). The one with ESRs only have ripples of around 1.7 for the same sizing.

So now what?

I did find this:

Converting Vpp to Vrms: (Vrms = 1/ (2 ×√3) × Vpp)

VRMS / Capacitor ESR (ohm) = Ripple Amps

The capacitors that I do see are between 400mohm and 600mohm when rated, so that calculates to be 15 amps at best.

So it looks like I would need to increases my capacitance to decrease my ripple and would also end up with more paralleled capacitors increasing my ripple abilities.

Am I doing this all right? What about the capacitors with no ESR rating but great ripple rating?

 

hope this helps:
http://www.endless-sphere.com/forums/viewtopic.php?f=30&t=31804