# Can TWO power supplies act as ONE bigger power supply?

Discussion in 'Electronic Design' started by Bilal, Aug 29, 2003.

1. ### BilalGuest

Would connecting two power supplies of 12 VDC 6 Amperes,
in parallel, be equivalent to a practical 12VDC 12 Amperes power
supply?

If yes, can this trend be expanded theoretically for say 'N' number
of power supplies to be equivalent to one power supply capable of
delivering N X 6 Amperes ?

-Bilal

2. ### Rene TschaggelarGuest

Theoretically yes, practically no.
They tend to have output resistances close to zero,
so when they are not within mV, they don't share the load.

There are loadshare controllers that would the expected
behaviour when the feedback was accessible.

Rene

3. ### James MeyerGuest

Pardon me, but I must say "Bullshit".

The supplies don't have to share the load at any output current less
than the rating for one supply. While the output current is increased from
zero, one supply may provide all the current. But that will happen only until
that supply reaches it's current limit. At that point, the supply with the next
lower output voltage will begin supplying current. As the current is increased
further, that will continue until all the supplies have reached their current
limits. Beyond that point, the output voltage will, of course, fall.

You should have said, "theoretically no, practically, yes".

Jim

4. ### Winfield HillGuest

James Meyer wrote...
We're very current, look how the first four lines all end.

Anyway, yes I agree completely with you Jim, but one point.

Some power supplies aren't really designed to run continuously
at their current limit, and therefore aren't well suited for
such usage. Often one sees explicit mention of the viability
of "parallel" connections in the sales brochure if the supply
can well handle this use. Other supplies have a connector in
the back, etc, where a wire going between supplies can insure
"load sharing" which means that both supplies will operate at
an equal fraction of the load. This is less common, but means
the paralleled power supplies will operate under less stress.

Thanks,
- Win

5. ### petrus bitbyterGuest

Bilal,

Yes and no. As so very often it depends. This time it depends on the
properties of the supplies. Some are even build to make it possible to use
them in parallel. Others may blow at once. I ever met the circumstance that
one PSU was not enough, so it switched off. Using two of them in parallel
they ware pestering each other until one switched off, followed by the other
as it could not handle the load alone. The solution (quick and dirty) was
providing more load to keep both power supplies busy. Don't laugh, pure
simple resistors to consume some hundreds of Watts. So you have to do some
investigations. If the PSUs have no current limiter, you'd better forget it.
Good chance you blow them. Same applies if they are different types or
brands. If you have two of the same type and brand and you can adjust them,
try to adjust them as equal as possible. Some low resistance high power
series resistors may help to distribute the load current among both PSUs.
Try to get as much as data of these supplies you can get. Based on that
information you can do a try out.

pieter

6. ### Ira RubinsonGuest

I work on equipment that uses PowerOne supplies in a "master - slave"
configuration to achieve twice the current. These supplies have small 6 pin
connectors connected by 22 AWG to the same busbar.
Example: the busbar is supposed to be 5V.
Both the master and lave are adjusted down so that the busbar is 4.8V
The slave is adjusted up until the busbar is 4.9V
The master is adujustd up until the busbar is 5.0V.

7. ### Fred BloggsGuest

This will work just fine by Australian standards- so go ahead- parallel
as many as you can get your hands on.

8. ### Fred BloggsGuest

His bench is lined with crocodile hide and he uses a shrunken wombat
skull as a hood ornament for the car he drives while drunk from bad
Australian beer

9. ### Watson A.Name - Watt SunGuest

Not one of your better posts, either, Mr. Critic. It would be best
for everyone in this ng if you (collectively, as in you'all) steered
clear of politics. Not all of us 'Merkins agree with the current
administration's policy. But you invite us to defend it with your
criticism. And that only makes for harsh words. Just some friendly
advice - take the off-topic stuff to the appropriate ng. Stick to the

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10. ### Bill SlomanGuest

Go take a piece of Fred for going off-topic in the first place with
his introduction of "Australian standards". He's been poncing around
this newgroup being a Bush/Rumsfeld groupie since the start of the
Irak rumpus, and richly deserved a spot of counter-nationalism.

11. ### N. ThorntonGuest

Hi. Well you've had explained what happens with regulated current
limited supplies. Now what happens with unregulated unlimited
supplies, which are more common.

If they share the same V_out, and I mean accurately, not just
nominally, and if they have the same or close source resistance, then
they will load share happily. Transformer rectifier capacitor supplies
like this work fine if the TFs are the same type.

But if o/c voltage differs, as it often does with different supply
types, and regulation or source resistance differs (ditto), then they
will work upto a point but wont load share at all well. Under full
load one will generally cook, or eventually pop a fuse.

So, like most things in life, it all depends...

Regards, NT

12. ### Bill SlomanGuest

Your talent for extracting information from the internet seems to have
established that the guy would not have a successful career as an
interior decorator, even in Queensland, but this has little to do with
his competence as an electronic design engineer - as far as I know,
Australian electronic design standards are much the same as for the
rest of the developed world.

Would you care to produce a non-nonsensical response?
Incidentally, how do you shrink a wombat skull? The trick with
shrinking human heads was to extract the skull before you started the
shrinking process.

A non-shrunken wombat skull isn't all that big to start with -
scarcely big enough to figure as an (illegal) hood ornament for
someone who would cover his bench with crocodile hide - but again, if
he only drives the car when drunk on that well known oxymoron "bad
Australian beer", it won't get out of the garage.

13. ### Fred BloggsGuest

Anyone who asks if the parallel supplies have a current rating equal to
the sum- or is it some other derating factor?- is not a design engineer.

Just enroll the wombat in the Australian public school system, this
seems to have worked well on the representative graduates here.

14. ### Bill SlomanGuest

Which doesn't oblige or excuse an erroneous and misleading response.
The American system doesn't seem to do much for the capacity to draw
logical conclusions. Your evidence is based on the functional capacity
of the brains that have been subject to this treatment.

The correlation between best proxy we've got for functional capacity -
IQ score - and brain volume is bugger-all, and the correlation between
that and skull size isn't all that great.

Even if the Australian education system does try to shrink the brain -
and I must say that that is a proposition for which there is a lot of
evidence - this doesn't mean that the skull would shrink to fitwhen
the treatment was successful.

Persistently drinking excessive amounts of ethyl alcohol (ethanol)
definitely does shrink the brain, but alcoholics and ex-alcohols don't
have noticeably small heads - Dubbya being a case in point.