Paralleling computer power supplies
 

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?

Tnx,

Dale W4OP

Paralleling computer power supplies
 

On Dec 29, 10:31*am, "Dale Parfitt" wrote:
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?

Tnx,

Dale W4OP

It is something I looked in to one time. I hsd s few power supplies
and thought I would try it. I checked the outputs into a 10 amp loaded
and decided they werent a close enough match to even try. With no
voltage adjust on the power supplies I confess I gave up pretty
easily. If the outputs could be matched I would think this would work.
I would always try to use equalizing resistors. I have had bad
expeiences when I didnt.

Jimmie

Paralleling computer power supplies
 

"Dale Parfitt" wrote in message
...
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

Paralleling computer power supplies
 

Norm Mann wrote:
"Dale Parfitt" wrote in message
...
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

Paralleling computer power supplies
 

Is there a feedback sensing line for voltage regulation
in the computer supplies that is accessible?
One trick I've seen done is to diode OR
the supplies, with the sense lines on the common
supply bus, after the diodes. MACom did this
on the massive switchers we used in our old fiber
nodes at work.

Paralleling computer power supplies
 

Tio Pedro wrote:
Is there a feedback sensing line for voltage regulation
in the computer supplies that is accessible?
One trick I've seen done is to diode OR
the supplies, with the sense lines on the common
supply bus, after the diodes. MACom did this
on the massive switchers we used in our old fiber
nodes at work.


I'd vote for the diode method, moving the sense line to after the diodes
OR just adjusting the supplies for about .6V more than what you want to
compensate for the diode voltage drop.

Paralleling computer power supplies
 

"Tio Pedro" wrote in message
...
Is there a feedback sensing line for voltage regulation
in the computer supplies that is accessible?
One trick I've seen done is to diode OR
the supplies, with the sense lines on the common
supply bus, after the diodes. MACom did this
on the massive switchers we used in our old fiber
nodes at work.


There are no sense lines available externally on a PC power supply. You might
take a look at the article on modding PC power supplies at
http://www.pavouk.org/hw/en_atxps.html. It shows a typical schematic (albeit a
bit aged now). Look at it and you can see where you might bring the sense lines
out of a "master" unit and run them into the "slave" units. No guarantee that
it will work, but I'd rather try that approach before the diode or resistor
solutions.
Of course, your PSUs will be different from the schematic in the web page, but
it should be similar enough that you can figure it out.
--
Dave M
MasonDG44 at comcast dot net (Just substitute the appropriate characters in the
address)

Life is like a roll of toilet paper; the closer it gets to the end, the faster
it goes.

Paralleling computer power supplies
 

On Dec 29, 5:40*pm, "DaveM" wrote:
"Tio Pedro" wrote in message

...

Is there a feedback sensing line for voltage regulation
in the computer supplies that is accessible?
One trick I've seen done is to diode OR
the supplies, with the sense lines on the common
supply bus, after the diodes. *MACom did this
on the massive switchers we used in our old fiber
nodes at work.

There are no sense lines available externally on a PC power supply. *You might
take a look at the article on modding PC power supplies athttp://www.pavouk.org/hw/en_atxps.html. *It shows a typical schematic (albeit a
bit aged now). *Look at it and you can see where you might bring the sense lines
out of a "master" unit and run them into the "slave" units. *No guarantee that
it will work, but I'd rather try that approach before the diode or resistor
solutions.
Of course, your PSUs will be different from the schematic in the web page, but
it should be similar enough that you can figure it out.
--
Dave M
MasonDG44 at comcast dot net *(Just substitute the appropriate characters in the
address)

Life is like a roll of toilet paper; the closer it gets to the end, the faster
it goes.

As long as they use the same IC it shouldnt be too difficult to
figure it out even if the rest of the circuit is different.

Jimmie

Paralleling computer power supplies
 

On Dec 29, 10:31 am, "Dale Parfitt" wrote:
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?

Tnx,

Dale W4OP

Hey OM
With my credit union branch going bellie up they tossed out tons of
computers. I can imagine there is comp supplies aplenty out there now
I see the wires them selves acting as milli volt drops. I mean how
many ground wires are coming out 8? Just use one ground wire and they
act like resistors. Albeit you better load those puppies up so that
little 18 AWG ground wire will do it's balancing act. I remember
buying comp supplies at Dayton one year for 50 cent they only worked
good when I loaded the 5 volt up big tme. Probably rejects brand new
in the box.

73 OM
n8zu

Paralleling computer power supplies
 

"raypsi" wrote in message news:84c626e3- I remember
buying comp supplies at Dayton one year for 50 cent they only worked
good when I loaded the 5 volt up big tme. Probably rejects brand new
in the box.

73 OM
n8zu

That is not unusual. Many of those supplies require loads
or they will crowbar.

Pete