Norm Mann wrote:
"Dale Parfitt" wrote in message
news
Has anyone connected a pair of identical computer supplies in parallel for
additional current capabilities? Did it require a low R resistor to allow
for any mismatch?


Since you've asked a general question, I'll give a general answer.
The problem with paralleling power supplies is that the voltage regulators
will fight each other if they are not set to regulate at the same voltage.
Using a low value resistor to isolate the outputs will work, but it will use
power you may not want to waste and your voltage regulation will not be as
good. A technique that was used on mainframe power supplies was to put low
value resistors (actually, calibrated current shunts) on both outputs into a
common load. Then the regulator on one power supply would be adjusted so
that the voltage drop across its resistor would match the voltage drop
across the other resistor. Once the regulators were balanced in this
fashion, the resistors were removed from the circuit and the power supplies
were connected directly to the load. As long as the power supply regulators
tracked identically, there was no problem.

HTH,

-NM


Another method that is currently popular among high-end supplies is to
have a current command output and a current slave input. With proper
jumpering, you set up one power supply as a "master" that outputs a
current command, and have a bunch of "helper" supplies that _don't_
attempt to regulate voltage, but just supply current on command.

If you're _buying_ supplies to do this, I'd suggest hitting the surplus
places for general-purpose switching supplies. MPJA has a good
selection, and I recall being able to find the manufacturer's data
sheets with some digging. You can get much nicer prospects that way
than trying to hack a PC power supply, although it's not as cheap as
dumpster diving for PC parts.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" gives you just what it says.
See details at http://www.wescottdesign.com/actfes/actfes.html