switchmode PS rating 1

[kenre]

On a standard computer switchmode Ps i have, it is rated at 30A @ 5V, 25A @ 12V... etc. are these ratings total Eg, 30A
Max at 5V, with nothing on the other voltages, or can it supply 30A @ 5V, AND 25A @ 12V simultaneously ?

Ken

 

[itsmoked]

Those numbers are 'simultaneously', however, you better take them all with a strong dose of scepticism. A lot of those parts are living at warm temperatures with merely 'normal' loading.

I would say the MTBF (Mean Time Before Failure) would be a straight line going from maybe 200Hrs with full load, out to 5 years with no load. (seat of the pants).

Also a lot of people presume to use them for non-PC applications, and while possible, you must remember that PC power supplies are totally, (consumer), optimized for just specifically; 'the job'. Every fractional cent, (or yen), has been bred out of them for years, with otherwise nutty concessions made, 'because they can', as the application is so specifically understood. They are truly thoroughbreds for their jobs. Note: You can't use a race horse to pull a sled of logs.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[logbook]

I disagree. I have a relatively expensive replacement type in front of me. The +5V and +3.3V ratings are not independant.
It says
+5V 25A
+3.3V 6A
but they are bracketed together with a 125W max rating.
5x25= 125
3.3x6= 19.8
Total would have been 145W if not otherwise stated.

Like itsmoked says, they are tuned for cost. Typically a motherborad would use less 5V power if it used 3V3. It is called a 300W peak unit and yet the sum of the power rail ratings is actually only 260W.

 

[kenre]

200 Hours of life i can live with!! There cheap to purchase!

So it is possible to pull maybe 50A using only the 5v rail? for a limited amount of time?

Yes your correct, it is being used in a current controlled power supply, up to 30 amps @ 5V for hard chroming.

Next prob it to calibrate the amp meter....

Ken

 

[itsmoked]

50A@5V? Answer: Will last about a New York minute.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[itsmoked]

Oh and before you ask.. No you can't use two in parallel.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[kenre]

I dont need 50A, only 25 ish.

itsmoked, youve already answered my next question,
mainly out of cuiosity,and being how i am, can you explain why 2 switchmode PS cant be used in parallel?


Ken

 

[itsmoked]

Hi kenre; In a nut shell - the voltage regulators are designed to put out a specific voltage ~5V. In reality due to a truck load of variations a particular supply will not actually put out 5.000V but maybe 4.9V. The other might put out 5.0V. Well the one that is trying to put out 4.9V tries to throttle back because the 5.0V one is trying to raise the voltage up to 5.0V. This results in the 5V one doing all the work, so you get severe non-sharing. Careful matching and adjusting of the two supplies won't work either because as soon as the supplies start to warm up the voltages would minutely shift and the problem would reoccur.

There are ways but they often cost energy or, the supplies need to be designed for sharing.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[kenre]

Ahh ok! thankyou.

my limited electronics knowledge tells me if there was a diode in the outputs, there could be a chance of them working together?? Voltage drop isnt an issue.

I would prefer to use a transformer for the supply, but to find one with a large Amp rating, and at a realistic price (yeah in cheap, but also love to build all my own equipment) is proving to be the sharp pointy thing burried within cut folage

 

[itsmoked]

Well now.. If you don't mind losing er...wasting energy you can try two LARGE identical diodes. They isolate the two supplies enough that they can possibly share the load. This is because the diode with less current running thru it has a lower voltage drop which invites more current from its respective supply. See what happens.

Best is to ebay the supply you need. That way you can probably get voltage and current control.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com