Pico PSU

bugeyewrx · 18 Apr 2011 at 13:49

I've got a wide input pico psu that will accept 12v to 25v and a universal laptop power brick that will supply 15v to 24v so obviously I can set the brick to anything I want and it will still work .

What I'm wondering is does it make any difference at all what voltage I choose ? Is 24v better than 15v or the other way round or even something in between ?

Reaper 392 · 18 Apr 2011 at 13:51

if you have more volts, you should be able to get more power.

although my physics teacher was rubbish, i did learn that power (Watts) = volts x amps, and that most parts are limited by the number of amps, not volts

jak731 · 18 Apr 2011 at 13:56

Yeah the laptop brick should be able to provide the most power at 24V.

Are there current ratings on either? It's possible the laptop brick might not be powerful enough whatever it's set at.

bugeyewrx · 18 Apr 2011 at 13:58

I did think about P=VI but it's a 120W brick so more volts equals less amps ? .... then the pico psu does the whole P=VI thing again . My physic teacher was good but the 28 years that have past since he told me anything doesn't help .....

bugeyewrx · 18 Apr 2011 at 14:03

@jak731 .... I should have said it works fine more a question out of interest . No ampage ratings on either bit the the brick is 120W and the psu 80W (120W peak ) so the brick has plenty of power .

Tealc · 18 Apr 2011 at 14:07

The Pico PSU will be limited by the amount of amps it can provide to the motherboard in the form of 12v, 5v ansd 3.3v. I suppose in theory a 24v supply will provide lower current than a 12v one but this will depend on how the pico-psu converts DC to DC, as quite often voltage conversion can be quite inneficient.

If you have 24v to PSU then you have to convert voltages twice. 230v down to 24v down to 12v/5v/3.3v.

bugeyewrx · 18 Apr 2011 at 14:16

Tealc said:
..... as quite often voltage conversion can be quite inneficient.

Hhhmm so my pico psu says it is 94% efficient so I suppose that extra 6% is being turned into heat , inside the case . The brick set to 15V give the psu less to do so less heat in the case ( and more from the brick ) ?

JonJ678 · 18 Apr 2011 at 14:18

Tealc said:
how the pico-psu converts DC to DC, as quite often voltage conversion can be quite inefficient.

This is the crux of it. Neither device is going to be working at its best at either voltage extreme, so my "instinct" would be to set the ac adapter at 19V. At high voltages the pico psu will be struggling, at low voltages the ac adapater will be struggling to output enough current. I'm voting for 19V as it's the most common voltage used on laptops, and I think the design considerations which lead to that will be transferable.

bugeyewrx · 18 Apr 2011 at 14:21

Funnily enough it is set at 19V just because it's the common laptop voltage .