Alternate Power DC-IN on the Euler Bus also with PI filter for batt operation

[MarkHaysHarris777]

I've ordered a power supply to go the Euler Bus way. Not sure if I need the filter, but in case: do you have any idea of the value of the inductor? 

I typically pull the components from old PC mother boards or power supplies , where they have been used for this same purpose.  The inductor, sometimes referred to as a choke, can be as high as 10H (Henrys).  Depending on the size of the caps , and the amount of ripple in the line , can be as low as a few hundred mHenrys, as well. The caps can be anywhere from 500mF to 2000mF .   Usually the inductors can be physically smaller if they are soft-iron torroids;  but, composities are also available. Of course you know if the filter is effective by putting a scope on the output.  The ripple reduction of a low-pass filter on a scope is often dramatic. The first link below is a theory link;  the next two links are calculator links which may be used to design passive filters.  

http://www.learnabout-electronics.org/PSU/psu12.php

http://siversima.com/rf-calculator/lowpa...-designer/

http://www.calculatoredge.com/electronic...20pass.htm

Back in the day, we were filtering the 60hz or 120hz ripple from the half-wave or full-wave rectifiers. Today we're filtering the high frequencies of a switching supply, or the noise generated by an automotive dc - dc converter; or other electrical noise often picked up by a long dc power cord from a wall wart.