Re: newbe needs help?

Barry,

For your capacitor, I'd suggest you go for RS stock number 189-866
which is a 47,000 uF 100V, or maybe a 189-850 22,000 uF if you want
to save money. For the bridge, use a 183-4129 which is a 25A bridge
(negligible cost difference here between different different current
and Vrrm ratings).

I made my supply from a pair of 30v RMS 7.5A toroidal transformers
in parallel using the above bridge and a 100,000 uF 63V capacitor
giving a 42V supply. After some measurements whilst running three
motors at full speed and load, I removed one of the two transformers
as it simply wasn't needed. I found that a figure of 33% of the
calculated current was closer to the mark than the accepted 67% for
chopper drives, so you might well be able to downsize your
transformer to a 500VA (think about how little time a chopper drive
needs to be ON to supply 3 or so volts from a 40 to 80 volt supply).

Just my two pence (being in the UK :-)

Colin



--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Barrie Hopewell"
<bazo@b...> wrote:

> hi all
> been reading most of the groups emails for about year now and have

steadily been byeing the bits to build my cnc m/c but have hit a
problem with the power surrply which is I don't know what parts to
bye i.e. caps and rectifiers . the transformer I intend to bye is a
toroidal type 1000va 11.25A 48V with the secondary winding at
500va . so my questions are what does VA stand for, what sort of
rectifiers do need and what size and sort of capacitors do I
need ,for any uk people out there I am hoping to bye these from RS
so if you know any stock numbers would be most appreciated for all
the boys in the USA , I don't mind byeing from there if you have any
ideas all your help will be vary helpful

>
> many thanks baz
>
>
> [Non-text portions of this message have been removed]