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How do you compensate for power conversion loss?

S

Sly

Supreme [H]ardness
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Aug 17, 2004
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In the case of laptop's and netbooks. The basic rule i've been following is that you add 30% to the laptops TDP to compensate for the inneficiency of a power brick. So if a netbook is advertised as 12w, you actually think of it as 16w.

Does the same still apply to a nettop with a dedicated PSU? Those power bricks are only rated at around 30-40w. But the PSU's are 300w. Does the +30% still apply?
 
Depends on the efficiency of both the brick and the psu, you can probably google the make/model of each to find out what the total draw is. Start with the PSU and figure out the component draw from that. Then find use the efficiency to determine the psu's draw from the brick. And finally use the brick's efficiency to determine the brick's draw from the wall.

Using your current +30% estimate as a baseline you're looking at 77% estimated efficiency.

Following that concept with the numbers you've estimated you get these results:
40w output from brick translates to 52w draw from the wall. Of the 40 output from the brick, 31w goes towards the components with the remaining 9w being dissipated as heat in the psu. As a reminder this is with 77% efficiency on both brick and psu.

Edit: It does seem a little absurd to have a maximum of 40w being fed to a 300w PSU being that if the components drew more than 31w, additional power would have to come from somewhere.
 
I was just wondering how much electricity to expect from a nettop.

I'm currently using a netbook and this thing is incredibly efficient. Based on the battery's capacity and how long it lasts. Under full load my netbook was using about 12w from the battery. So i'm estimating that it's using 16w from the wall.

I'm trying to determine if i could get atleast the same efficiency as a nettop. Hopefully even more since it's going to be an Atom based web server and it doesn't need a monitor or any peripherals.

And even tho both the netbook and the nettop mobos might rate the same TDP, i'd like to know if they draw the same power from the outlet.

Why does a nettop need a 300watt PSU? While the netbook can run off a 30watt brick? That's like 20x more than what's needed. Am i forgetting something? Will having a 300w PSU make it use more power than a netbook?
 
Sly said:
I was just wondering how much electricity to expect from a nettop.

I'm currently using a netbook and this thing is incredibly efficient. Based on the battery's capacity and how long it lasts. Under full load my netbook was using about 12w from the battery. So i'm estimating that it's using 16w from the wall.

I'm trying to determine if i could get atleast the same efficiency as a nettop. Hopefully even more since it's going to be an Atom based web server and it doesn't need a monitor or any peripherals.

And even tho both the netbook and the nettop mobos might rate the same TDP, i'd like to know if they draw the same power from the outlet.

Why does a nettop need a 300watt PSU? While the netbook can run off a 30watt brick? That's like 20x more than what's needed. Am i forgetting something? Will having a 300w PSU make it use more power than a netbook?
Click to expand...

A 300w PSU means it can supply 300w to the components. Considering efficiency, at full load it would draw 400w from the wall MAXIMUM before the psu couldn't handle the load. The actual wattage is likely much less, it's just that psu's generally don't go lower than the 250w/300w range for most computers.
 
They could have used a 90W laptop power supply, but it probably came down to a matter of cost. For a stationary computer that won't be moved where the PSU isn't going to be manhandled and heat isn't a big factor, it might be cheaper to just make an oversize PSU that won't get hit with much load.
 
Woofer00 said:
They could have used a 90W laptop power supply, but it probably came down to a matter of cost. For a stationary computer that won't be moved where the PSU isn't going to be manhandled and heat isn't a big factor, it might be cheaper to just make an oversize PSU that won't get hit with much load.
Click to expand...

Good point. Thanks.
 
Not really much higher. My current one's reputed as the most power hungry one (msi u230 dual core. Considerably faster than a dual atom) and it's running on 18 watts. A 15" LCD runs on twice that.

Since the most power hungry component of a netbook is the LCD. I would imagine that a nettop would be running on less. I'm still planning on putting one together (isnt there an itx case without pci and drive slots?) and I think the only things you need are the mobo, casing, a gig of ram, and a small harddrive. No peripherals so it should be running on even less power right?

Ps: regarding all this concern about power. I don't have qualms about running an uber pc at full power occasionally (that's what it's there for), but a 24/7 server makes power usage a big deal.
 
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