Aspire One vs KillAWatt - Power Consumption Test (with pic)

Hows the wattage when it's charging the battery?

 

Ouch. So many mistakes and general exhibitions of cluelessness I hardly know where to begin.

"Found out the power factor was about 50%."

How did you measure the power factor? Pics or it didn't happen.

"That means the power supply is clipping the AC waveform and causing a reflection back through the power meter out back"

No its does not. 50% PF It means that for every watt delivered to the load, another watt is being dissipated as heat. There will be a little bit of RFI-EMI noise coming back the line, but no significant distortion of the AC waveform, that would require inrush current draws many orders of magnitude higher.

"making me pay almost twice as much for the electricity"

Making me pay for twice as much electricity as I would have had to had the power supply been 100% efficient.

"I'm going to size up a capacitor and improve the power factor"

Increasing capacitance at either the input or the output stages will not improve the efficiency. The heat is being lost mainly in the switching diodes, and the pass transistor on the output voltage regulation stage, and depends on the design as well as the choice of components.

The cheap, low power switching modules used for provide DC power for laptops are not especially efficient. They're fine though, since most of the time the laptop is drawing less than 10W, so whether the efficiency if 50% (very poor) or 90% (impossibly good) the difference is only 4W. Most of these switching supplies are rated about 70-80% efficient, but the actual efficiency varies with the output load.

So don't sweat it, and for the love of Pete don't start modding you're power brick.

 

Geez goofball, what is you're problem? Idle is idle. For the purpose of the discussion, "Boot but do not touch" is more than adequate. Whether you have the mail application open or not, whether there are background processes running or not, whether you are browsing the web even ... none of these consume significant CPU or GPU cycles. The monitor brightness setting makes far more difference to the power consumption.

Most people will have the Aspire One at close to 0% average load for most of the time they use it, which is why idle power consumption is a far better metric than 100% load. The same can be said for all computers in a home or office environment. The only exceptions where a consumer machine sees sustained heavy load is media encoding and gaming, unless they run a folding at home-type distributed computing app.

 

This one calculates RMS values, so the power factor should be close.

I don't think you understand power factor.

Very little heat is lost in the switching diodes. The one volt voltage drop across a pair of diodes in the bridge configuration is insignificant over the 170 volt peak to peak voltage of a 120 volt main. The heat from these diodes is small compared to heat from the slew rate limitation of the switching transistor. Regardless, this heat isn't being bounced back into the line.

Ever operate a transmitter and have a mismatched antenna? The power reflects, heating up the amplifier. This is what happens when the load doesn't match the source.

I can measure it on my utility meter too. Its a very big difference. I have an old surplus 10KVA Exide 10/12 UPS unit for our house. It has a horrible power factor. Each time its power supply clicks to bump up the capacitor bank, the utility meter jumps. Running with the UPS for a month pushes my electric bill quite a bit. I hooked a scope up to the incoming mains and the current took quite a notch out of the line. Just your simple switching power supply, but on a much larger scale.

Most people install KVAR correction close to the mains distribution where it is practical, not across each individual device.

 

Someone asked how many watts when charging a battery.

29 watts at .48 power factor, or 58VA.

 

I was under the mistaken impression you meant efficiency rather than power factor. I see now you were really talking about power factor .. basically watts/(voltage x current). How accurate your meter is for measuring power factor for non-sinusoidal waves notwithstanding, I see from your photo (thanks!) that you do indeed get a reading of 0.5.

Now remember this is not the efficiency of the power supply. The only power being "wasted" is in the transmission losses of pushing the current back and forth. So say your aspire one power supply draws 10 watts, at PF 0.5. So, if I've got my square roots lined up right, this means it pushes a max 40 VA. (1/0.5)^2 But your utility still bills you for watts used (the 10W) not VA, so you dont pay any more. (Think of it working like 40 watts from the power company + 30 watts pushed back to the grid, the total is only 10W, but the power company has to support the 40 watts worth of current draw which is why if you're using a low power factor in total they might have a surcharge)

Unlike your 10kV UPS, the power factor of the Aspire One's power brick isn't something to get worked up over. You don't pay any more, and it isn't going to cause your utility company any headaches either!

 

Yes, while charging my AAO pulls about 30 watts.

As for RJM and dattaway.

Where in the world are you where your electric utility makes residential sites pay for PF correction? I'm pretty sure only commercial/industrial sites have to, not residential.

What waveform clipping are you talking about... There isn't any

What heat are you talking about being lost in switching diodes??? reflected power is just that... reflected. You were right the 2nd time though, you do get losses through (re)transmission.

You say low PF isn't something to get worked up over. Yea, well that may be the case until 2014 when (USA) federal law mandates the use of only compact fluorescent lights. Computer PSUs and CFLs are notorious for bad PF. Power quality is going to go through the floor, and we're going to have to start working on a fix. The harmonics that these switch mode supplies generate turn back into heat at the transformer level, reducing the lifespan of the components - which eventually lead to failure and since monitoring isn't up to snuff right now. Don't worry, I'm actively working on a solution seriously.

 

I've seen that you try to measure the power consumption of the AA1. Try the Notbook BatteryInfo, available at www.batteryinfo.de.vu . It will show the current power consumption as reported by the battery controller. It is more precise than the measuring on the power network side. Of course, this can be done when the netbook runs o battery power.

 

I' d like to know what the power consumption is when downloading (wifi on , utorrent downloading through wifi, screen off).

If someone with a killawatt could do such a test, I' d be grateful, as I don't have one... Thanks

 

Possibly this has been mentioned, but if you install the notebook battery info program, you can watch a real time display of the power consumption.