Re: Newbie: power supply voltage and current requirements

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "iseechipsfly"
<menglish@s...> wrote:

> Hello,
>
> Being new to the group I'd like to ask for assistance with regard to
> an appropriate power supply for the CNC router I've built. The

motors

> I planned to use are the Vexta PK-268M-02A wired as bipolar. At
> bipolar the specs call out 6.3V at 1.4A; at unipolar they are 4.5V

at

> 2A. The controllers are Centent CN0143 24-60V input and 1.5 -
> 14A/phase (these came with other used surplus parts; Geckos in the
> future :) The breakout board is a Sound Logic Model M2 (Mach2).
>
> What is the least voltage and current (for the PS) I should be
> considering?
>
> Could you recommend an appropriate power supply (parts, kit or
> assembled) that would work for the above system? I've read where the
> recommended power supply should be ~ 20x of the stepper motor
> voltage. With the bipolar voltage at 6.3V and a max 60V at the
> controller, even 10x is not possible.
>
> Thanks for the help.
> Mike

Well, there is some good news and bad news here. The current
requirments are minimal so if you are planning on using 3 motors the
peak current would be 4.2A but that is with all three motors stalled
so under normal operating conditions a power supply capable of 3A
continuous should work fine. The 20X is a target for max RPM. If
you can approach 10X you will be able to get some decent speeds. I
would look at using something in the 48VDC range since that is a real
common voltage. The closer you can get to 60VDC the better. The
design can be pretty simple with a transformer rated at about 70% of
the final desired DC voltage, (see explaination below) a 6 - 10A
bridge restifier with min 200PIV ratings (Can be higher) and large
filter cap of 10,000 to 25,000 mfd at 1.25 times the max DC voltage
(or greater). A 75VDC working voltage on the cap for a 60VDC is
about right. Put separate fuses in each DC run to each controller of
about 5A and you have the basis of your design. Fuse the primary of
the transformer with a 3A slo-blow fuse.

A note about the transformer. The AC output of the winding when
rectified by the bridge is 1.4 times the AC RMS voltage.
Transformers are rated at RMS volts. To get 60VDC (disregarding
diode drops and IR losses) you would need a 42 to 43 VDC secondary at
3A. A 36VDC transformer will give you about 51VDC at the filter cap.
Bulk power supplies are designed using the average current draw of
the system not the peak. (Unless the peak is for long periods or many
times the average).

See www.MPJA.com for surplus transformers and supplies.