Re: [CAD_CAM_EDM_DRO] Re: Question on Power Supply - regulated notes

m0nkey0ne wrote:

>This is an interesting and informative thread. Please don't stop!
>It may have been repeated, or way beyond the technical knowhow of
>some of us, or so utterly simple it should have already been known,
>
>

The only thing I want to point out is the use of the zener diode, as
I've done in my supply.

Here is a description of the power supply setup I'm using.

My transformer is a 750VA 440-120 stepdown transformer that I found on
ebay for $10. With USPS flat-rate shipping it cost me $17. I run the
primary at 120VAC to get a secondary voltage of about 30VAC. After the
rectifier and the filter cap its a bit over 40VDC. To this I add a 39V
zener (the wattage of zener is chosen based on how much current it will
be handling when the supply is unloaded). This clamps my final voltage
to no more than 39VDC. Any overvoltage at the primary resulting in
greater voltage on the secondary is dumped through the zener, providing
some protection to the controller board.

Since I am not using an optically isolated controller board on the
parallel port I also connect the ground terminal of the power supply to
the chassis of the computer. This ensures equal ground potential between
the DC supply for the controller board and the parallel port. The power
supply and controller board are installed inside the computer chassis,
and both the DC supply and the computer power supply are isolated from
the line, so in theory it should all be safe. There is a link to an
image of the power supply and controller installed in the machine below.

The control board is 4 axis with a limit of 3A per axis, so max current
draw should be no more than about 12A at 39V, or around 470W. The
transformer is rated 750VA, or about 540W, so it should be well within
its capacity, even at peak power on the controller board. In practice I
never have all four axis at full current draw. With coordinated moves
on my machine its not possible to rapid at full power with more than 2
motors. Under full load (2 axis rapid moves at 95ipm, 3 axis at
20-something) I measure about 0.7V of ripple on the DC supply. The
transformer temp never rises more than a few degrees above ambiant.

Overall, its a very low-cost supply with ample power for my needs.
TurboCNC on a P4/1.8Ghz machine driving a HobbyCNC board and 200ozin
steppers gives me 95ipm rapids on my Taig mill. There is a link to a
video of the machine pretending to be a plotter below.

Here are some images of the machine:

Overview of machine and controller:
http://codesuidae.net/images/MillSetupTemp1.jpg

Back of computer showing motor wires:
http://codesuidae.net/images/ComputerBack1.jpg

Power supply and controller board installed in computer chassis:
http://codesuidae.net/images/ComputerSide1.jpg

Drawing some text using 95ipm rapid rate:
http://codesuidae.net/images/mill/taigengrave.avi

Dave