I'm really annoyed and should probably just be confused... They always sell Pico PSUs rated at 150W with bricks that only out put about 90W. Am I missing something?
For Example
For Example
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Pico PSUs
- Thread starter tmclaugh
- Start date
- Joined
- Apr 12, 2003
- Messages
- 7,534
Efficiency 
Efficiency
That's about what I was going to say. The Pico PSUs actually use a 120/220V to 12V converter which converts the incoming AC electrical signal to the 12V required for the Pico PSU to operate. As a result, to deliver 150W @ 12 VDC worth of output the Pico PSUs draw 80 to 90 W (@ 120 VAC) from the AC mains socket.
This is where I get confused though
- on the back of the brick you multiply amps and voltage to get total watts going into the PC and usually it's way less than the what the PICO PSU can output. I assume I'm missing some conversion process but I'm curious what it is.
- on the back of the brick you multiply amps and voltage to get total watts going into the PC and usually it's way less than the what the PICO PSU can output. I assume I'm missing some conversion process but I'm curious what it is.
Efficiency
Wow. Just... wow. I don't understand why efficiency is such a difficult concept for some people to grasp. And you only need 90w @ 120v to deliver 150w @ 12v? What?
Watts = Volts * Amps. Until you develop a power supply that somehow exceeds 100% efficiency (in which case I suspect someone will be wanting to award you a Nobel prize) there is no way to make 90w at voltage a equal 150w at voltage b. You decrease the voltage but the amps increase correspondingly, wattage remains constant. Factor in the fact that no real-world power supply will ever achieve even 100% efficiency, and input power must always be higher than output power.And computer power supplies-indeed, all of the power supplies I've ever dealt with irrespective of their application-are rated on their DC output power, not their AC input power.
You have two 100w, 12vdc power supplies. One is 80% efficient at full load, the other is 90%. Both have a maximum output of 8.3a. 8.3*12=~100w.
However. The 80% efficient unit will consume 125w of power to generate 100w of output; the remaining 25w is dissipated as heat. The 90% efficient unit will consume 111w, with 100w of output power and 11w of heat dissipation.
Now.
No, you're not missing anything. The power brick for that unit is rated at 12v @ 6.6a; again, v*a=w, so it's an 80w power brick. Which effectively makes the PicoPSU it's attached to an 80w power supply. If you gave it a beefier 12v power brick, it'd be able to hit its rated 150w output (assuming the components on it aren't optimistically rated), but as it stands, it's effectively an 80w power supply with a 150w label.
Wow. Just... wow. I don't understand why efficiency is such a difficult concept for some people to grasp. And you only need 90w @ 120v to deliver 150w @ 12v? What?
And computer power supplies-indeed, all of the power supplies I've ever dealt with irrespective of their application-are rated on their DC output power, not their AC input power.
You have two 100w, 12vdc power supplies. One is 80% efficient at full load, the other is 90%. Both have a maximum output of 8.3a. 8.3*12=~100w.
However. The 80% efficient unit will consume 125w of power to generate 100w of output; the remaining 25w is dissipated as heat. The 90% efficient unit will consume 111w, with 100w of output power and 11w of heat dissipation.
Now.
No, you're not missing anything. The power brick for that unit is rated at 12v @ 6.6a; again, v*a=w, so it's an 80w power brick. Which effectively makes the PicoPSU it's attached to an 80w power supply. If you gave it a beefier 12v power brick, it'd be able to hit its rated 150w output (assuming the components on it aren't optimistically rated), but as it stands, it's effectively an 80w power supply with a 150w label.
I stand corrected.
if you want to get a full 150W out of it, you need to find a beefier brick, like the Dell DA-2, which is rated @ 220W. Its also massive, and requires special connectors on the back of the case to handle the higher amps.
You'll find many of the higher watt AC-DC bricks output a higher voltage like 19V so that the amps going over the DC output cable is not excessive, so make sure you find one that is 12V output.
You'll find many of the higher watt AC-DC bricks output a higher voltage like 19V so that the amps going over the DC output cable is not excessive, so make sure you find one that is 12V output.
Thanks. I actually had a 200W PSU with a dell DA-2 that recently died and am setting up another one. I just wanted to be sure that going to all of the trouble of modding it out was worth it. It's ridiculous that they advertise 90 - 150 Watts in some of these packages and then throw a crappy less powered brick in there.
Thanks for confirming my suspicions.
Thanks for confirming my suspicions.
The Pico PSU's don't regulate the 12V supply they get from the brick, so you can bypass the Pico entirely for the ATX12V connector with no ill effects (take one of the 3 12V lines from the DA2 and just hook it up to the mobo). Worth it if you want to exceed 150W.