I am trying to find out how many watts are drawn by the consumer power supplies used by my home modem, router, and laptop PC. These are the small, standalone power supplies that plug into the wall and then supply a low voltage, typically 12 volts or so, to the devices. The print on these things is so tiny I can't read them, the manuals don't seem to say, and I can't find the info online either.
Approximate wattages would be fine, I'm trying to find out if it's 2 watts, 5 watts, or 20 watts, or 50 watts, give or take a little. For what it's worth, my modem is a Westell 6100g, my router is a Linksys home router (forget the exact model #, the power supply supplies 12V,
1 amp), and my laptop is an HP G72.
If you happen to know exact wattages for the power supplies that come with these devices, then great, but again, approximate ranges are very helpful as well.
They vary. A lot. Buy a Kill-A-Watt meter, or another meter (that one happens to be pretty good bang for the buck in solving this sort of thing.)
12V, 1 amp is 12W. Might be 15-20 W AC with typical inefficiency in the AC/DC conversion. Might also be 8W if the power supply is capable of supplying that much but the device does not actually draw that much. Likewise, the laptop will draw much more when charging the battery than when running with a full battery.
It varies a great deal by device, even within a general category, and may vary quite a bit by the device's current activity level. I'd guess that DSL modems, and firewall/router devices are probably in the 5-watt range these days.
You might want to consider buying or borrowing a "Kill-A-Watt" device... plug-in power measurement meters. I'm told that they aren't supremely accurate, especially when dealing with devices that have a relatively poor power factor or draw current from the line in irregular pulses, but they'll probably give you a decent ballpark estimate.
Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
Actually, they deal perfectly with these devices, as they will happily report (directly) on Watts, Volt-Amperes, and power factor - ie, they are not making any dumb assumptions about all loads being high power-factor sinusoidal. Perhaps whoever told you that was not paying attention. Or perhaps one or both of you have standards for "supreme accuracy" that don't pay much attention to paying $20 for a device instead of $20,000, in which case I'll let you worry about each 10,000th of a VA in peace.
Mine has recently been looking at my cheap shop lights (PF .52 or so) and the one I replaced the ballast in (.99 or so - quite difference a good ballast makes.) The wattage draw is similar, but the VA is night and day, as you'd expect given the PF, considering what the PF reports on.
The two annoying things about them are that they lose everything (it's mostly the accumulated KWh data you'd want) on the briefest power outage, and that they cause a yearning for one that deal with 220 loads (see a recent post in components for something that helps with that, though it does not do KWh, nor calculate VA for you, but you can calculate VA from what it tells you).
Wait there is a third thing - intense cold gives than them the willies - not sure if it's just the LCD freaking, but it was no good in my unheated shop in the winter.
For figuring out what your computer crap (or other plug-in 120V devices) is costing you, it's the bee's knees, as you can both look at what the draw is under various conditions (such as charging the battery or not) and also what it comes to over a day or a week (so long as there are no outages of any duration during the time of measurement.) Can make very plain that your old fridge or air conditioner or dehumidifier really is costing you a lot more than a newer one, if you can plug in to both types (if you don't have two of different ages, try a neighbor or friend with a newer or older type than the one you have) for a week or so of use.
The power ratings of the supplies aren't relevant; what matters is the power drawn by the device connected to them. The supply must be able to provide at least as much current as the device draws, but it doesn't matter if it's capable of supplying more (invariably, it *will* be capable of supplying more, as the manufacturer will pick the "next size up", i.e. the cheapest supply capable of supplying at least as much power as the device will require).
Also, while the modem and router will typically draw a fairly constant amount of power, the laptop's power consumption will vary depending upon what you're doing with it. A typical GUI application spends most of it's time waiting for the next key press or mouse click. In this state, the computer will draw relatively little power. If you initiate a task which requires significant processing power, the power consumption will increase while processing is being performed, then return to normal once processing is complete. You could easily see a ten-to-one difference in power consumption between busy and idle.
Ultimately, the only way that you will get useful answers is to actually measure the power consumption with a Kill-a-Watt or similar.
If there are no other indications then 12W is a fairly good guess. But some mobile phone and drill chargers are smart enough to draw nothing when not connected to a load.
And you do find badly designed kit that draws way more than it should when switched off or in standby. Daftest one I have seen is a PC 5+1 sound amplifier that draws 20W when "switched off" and 21W when switched on and silent. This is despite having a mechanical switch!
Other common hogs are TVs and set top boxes that have their digital decoders running all the time by default (so the video can record off the air). This can be altered. Some devices in standby draw much less than 1W so campaigns against standby buttons are hopelessly misguided.
The only way to be sure is buy one of the devices that sits in between the device under test and the mains (approx £10 in the UK).
Well, one way is to just guess the power by the weight of the supply. If it's an old linear supply, it will weigh more due to the heavy (60 Hz) iron core transformer. But the new little switching supplies weigh much less. I have one here that measures about 2 X 2.5 X 5/8, weighs
2.5 ounce and delivers 5 volts at 750Ma (3.75 watts). Another measures
3.5 X 2.25 X 1 3/16, weighs 5 ounces and delivers 24 volts at 500 mA or 12 watts. So, you can extrapolate from there. Looks like about 2 watts per ounce, plus or minus a little bit. Add a little wattage to the larger ones and take off a little bit for the smaller ones. Larger ones are more efficient, and packaging doesn't count as much.
Typical wall warts are not often more than 15 W. Bricks can hit 110 W or more. Most manufacturers will try to say under 50 W; then it can be considered a Class 2 or Class 3 power limited device and has less difficult fire safety requirements.