Need info on Capacitor(s) for power supply

[Jackal66]

I was wondering about the different capacitors you see on power supply's ( home retrofits).

There are some that have one large cap the size of a soda can, like my Hurco KM3P.

Then, there are a few that have 3 caps, with one on each axis.

I saw one the other day that had (6) huge capacitors on it.

How do you figure what/how many caps you need? How many uf in the ratings?

Are these going from the power supply to the servo drives/amps to keep a steady stream of uninterrupted current?


This is one thing that gets me confused when I try to follow someone's build.

I under stand how the capacitor works in starting a RPC.

Usually someone can explain something like this in layman's terms and I can grasp it. This just hasn't been described in the sources I've been to. Probably most comprehend it way before getting involved in something like this.

Thanks in advance for the help.

Jackal66

[Bubba]

Jackal66,
Power Supply Capacitor rating Capacitor size?
Mariss has a formula that is conservative, and WORKS:
C=80000 x I/E where C is in microFarads, I is in Amps, and E is in Volts

Hope this helps.

[Al_The_Man]

Originally Posted by Jackal66 There are some that have one large cap the size of a soda can, like my Hurco KM3P. Then, there are a few that have 3 caps, with one on each axis. I saw one the other day that had (6) huge capacitors on it. How do you figure what/how many caps you need? How many uf in the ratings? Are these going from the power supply to the servo drives/amps to keep a steady stream of uninterrupted current?

Capacitors are used to decrease the 100% 120Hz pulse ripple on the output of a bridge rectifier, IOW attempt to provide steady state DC.
The higher the capacitance the less percentage of ripple at the rated current.
With no current flowing the ripple will be 0%.
They can be used in parallel to increase the capacitance value.
The balance is a capacitance value that will provide an accepted ripple at the maximum current.
A conclusion might be that the higher the capacitance the better, the down side is that a higher capacitance than necessary results in a higher required VA rating of the supply transformer.
Al.

[Jackal66]

Thanks guys,

That explains the "why".

I looked a Bob Campbell & Larken's power supply building diagrams, now it makes sense.

Thanks,
JAckal