Power Supply Efficiency Question

[thedhgroup]

So what would be more efficient?

1 48V power supply rated at 90% efficiency

or

4 12 volt power supplies in series where each supply is rated at 90% efficient.

I'm thinking the 48V supply is most efficient in the end but I have a hard time believing 4 supplies in series would be %60 efficient. Or would it? How does a person calculate this stuff?

Thanks,

TDH

[Kevin Dougherty]

Perhaps

.9x.9x.9x.9=.6561%

[Willie Williford]

A quick search found this:

Tutorial: Power Supply Efficiency

Any help?

Willie

[thedhgroup]

Originally Posted by Willie Williford

A quick search found this:

Tutorial: Power Supply Efficiency

Any help?

Willie

Kinda helps... Now I have to do ...math...

To get real numbers I may need to literally measure Input Vs Output. I'm better with a multimeter than I am with a calculator.

[Cobb]

I think 1 of anything is always more efficient than several smaller ones.

[thedhgroup]

Originally Posted by Cobb

I think 1 of anything is always more efficient than several smaller ones.

I agree, the question is how much more efficient. Smaller supplies (isolated outputs) are cheap but may be so inefficient that it is impractical. Then again if the setup is only marginally different, it might be OK.

[samwichse]

Originally Posted by Kevin Dougherty

Perhaps

.9x.9x.9x.9=.6561%

I don't think it works this way though, because the output of each supply isn't dependent on the output of the previous one... each one is independent. It would be like that you had several in a series that halved the voltage like: 96/2 @90% -> 48/2 @90% ->24/2 @90%...

But 12+12+12+12 @90% each should theoretically be the same as 48v @90%.

Think:

12v output @ 350ma is 4.2w output, meaning 4.62w had to go into it.

4.62 + 4.62 + 4.62 + 4.62 = 18.48w for 16.8w output in a series.

Now whether you'll find a cheap, small output supply that efficient is another thing (not likely, IMO).
Sam

[thedhgroup]

Originally Posted by samwichse

But 12+12+12+12 @90% each should theoretically be the same as 48v @90%.

Thanks Sam for putting some clarity to this. It makes sense. I have some laptop power supplies. A little bit of research suggests that they are barely over 80% efficient.