Re: Power Supplies

--- In CAD_CAM_EDM_DRO@yahoogroups.com, Dave Shiels <dshiels@e...>
wrote:

> There seems to be a lot of regulated DC power supplies On Ebay for

well

> under $100
> These look like lab equipment and many have adjustable voltage and

current.

>
> Is anyone using these as power sources in there CNC setups?

While there is nothing inherently wrong with using a regulated PS in
a CNC design (and if it has settable current limit a possible
advantage) BUT here are the negatives:

Linear regulated supplies will have electronics in the output
(usually large "pass transistors". They abhor being back biased.
What that means is that if they see a condition where the load they
are running is stuffing voltage back (like the back EMF from a
motor), currrent flows backward and transistors turn into fused
links. An output diode pointing towards the load (cathode end) that
will handle the current will protect it.

Another problem is that regulated supplies that handle over 3A and
have outputs higher than 48V are rare. I you need more than that you
will probably have to go the transformer/bridge/filter cap route.

One trick you can use is to consider just tapping off of the
unregulated voltage at the big filter cap. you will find the raw DC
voltage to be 6 to 15 volts more that the required regulated output.
I built a 30 volt supply for a buddy by doing just that from a 15V 6A
regulated supply. By picking the low line voltage tap on the
transformer I got right at 29.5VDC out of the raw side. Of course no
regulation or current limit, but I bought the supply for 15 bucks so
it was a DEAL!

If you can buy a regulated supply for less than the componets to
build an unregulated one then do it.

While you can use switchers if you know how to add output filtering
there is no "raw" DC to pick off. They switch the primary voltage to
get the exact output they want.