Need Help!- 24V from SMPS power supply ...

[CNCpatriot]

Hi ,

Iam trying to build a DIY CNC router.
Iam using stepper motors, whose drivers need 24V power supply & controller needs 5V supply.

Iam wondering whether I can connect 2 SMPS supply from standard PC in series and get my 24V for the stepper drivers.
PC powersupplies are very cheap, and give enough amps needed for steppers, but give only 5V & 12V.

Looks like the COM of SMPS voltage is connected to the chasis.
Iam thinking of isolating the COM from the SMPS chasis and using 2 SMPS in series.

Have any one tried this?

regards

[xatxtal]

The quick answer is yes, the following link will tell you how.
ProCooling.com
I have tried it and very satisfied.
Trevor

[CNCpatriot]

Any idea why resistors are to be connected across the 5V? ( as suggested in the procooling site)
I was planning to use the 5V to power my controllers. So dont understand why he has suggested to connect lowOhmHighWatt resistors across the 5V.

regards

[doorknob]

This is just a guess, but apparently some PC power supplies will not produce any output unless they sense a sufficient load current on the 5 volt rail.

So the resistors may be providing such a load to ensure that the power supplies function properly.

[xatxtal]

Switch mode power supply's normally need a load to work, as PC power supply's normally supply 10s of amps so the little current used by your driver boards would not be enough to kick start the power supply.
You can still use the 5v supply.
The following link may help as a resistor is built in and it shows the other lines are good.
PC Power Supply Tester 20/24 Pin PSU ATX SATA HDD on eBay (end time 09-Feb-11 07:44:37 GMT)
Or do a search on Ebay for "PC power tester"
they are so cheap from Hong Kong it is worth having.
Trev