Re: resistor for power supply

Hi,

Sometimes an "inrush current limiting" resistor is used to limit the
initial capacitor charge-up current. This usually a negative
temperature co-efficient resistor, meaning the hotter it gets, the
lower its resistance.

Usually they are necessary for off-line (115VAC or 220VAC) rectifier
and capacitor power supplies because there is no transformer present
to offer resistance and current saturation to limit current.

Mariss

--- In CAD_CAM_EDM_DRO@y..., "cadcamcenter" <cadcamcenter@y...> wrote:
> Hi all,
>
> So far all the suggestions for the power supply for drives shows
the
> connection from the output of the bridge rectifier direct to the
> capacitor (some may have bleed resistor, LED etc in parallel)
>
> An power engineer (who may not have very much experience with CNC
> items) mentioned that there will a large current surge on initial
> power up (when V on cap is 0) and suggested putting a resistor. My
> interpretation of his suggestion
>
> rectifier R
> . .-----/\/\/\-----
> / \ |
> / \ _____
> / \ _____ C
> \ / |
> \ / |
> . \./---------------
>
> What does the list think? And if this is an improvement what kind
of
> relationship R = function (C,I,etc) should there be between R, C
etc.
>
> A million thanks to the list
>
> Peter