What will my computer use through an inverter?
Computers are very much a part of our modern society even for many people living in the bush. Consequently, we are often asked to design systems for people wishing to use renewable energy. For the home or small office there are two main choices - a conventional desktop or a laptop.
We have measured the power consumption on the AC side of a number of computers (without the monitor). The results were:
286 vintage 27W 386 DX 43 486 and 2 drives 40 Pentium 51 Pentium II 56
We also tested several monitors.
14" monochrome 19W 14" colour 60W 15" colour 80W
In April 2001 we measured three Pentium III computers in a shop with 15, 17 and 19" monitors. They all used about 125W measured on the AC side.
The wattage of the following systems (with monitor on) was recently measured on the DC side of the inverter. (Selectronic sine wave).
Pentium 100 & monitor 120W AMD K6-2/450 & 15" monitor 112W Pentium 200 & 15" monitor 117W
I recently purchased an AMD 1300 MHz computer with 20GB hard drive, CD writer, modem and 15" LCD monitor. While running as the only load on a 1600W Selectronic SE22 inverter the computer without the monitor used 120 Watts but only an additional 80W if used while the TV was on. The 15" LCD monitor used an additional 12W.
Apple computers used similar amounts of power. Without the monitors, we have been given the following figures: Apple Power Mac 7600/132 - 75 Watts Apple Power Mac 9600/232 - 95 Watts Apple Power Centre 120 - 65 Watts
So to conclude, we would suggest a desktop computer will use 50 - 70W plus 60 - 80W for a monitor (12W for LCD) plus inverter losses of 10- 30% (depending on the size and efficiency of the inverter and whether or not other loads are on at the same time).
The other option is to consider a lap top. In general, we have found that these draw about 1.8A @ 12V (about 24W) on the DC side. One problem is that most lap tops run on something like 18V. We've found the easiest solution is to run the lap top off our micro inverter which retails for AUD$121. So a lap top is in the order of 8 times more efficient than a standard desktop. This means that one 60 - 80W panel could run your lap top for 8 hours per day. Unfortunately, lap tops have some limitations and are more expensive to buy and repair than desktop units.
Using an ISDN modem on an inverter
In Australia there is a Telstra Service for Internet users called ISDN. In brief, this service gives you a second phone line and a 128K- speed modem (64K when the phone is being used). Telstra supplies the 'modem' device. The service offers Internet speeds 2-3 times faster than a normal 56K modem dial-up service. It is available in many areas where ADSL is not available.
Now that the ad is done, the electrical requirements are easy and straightforward. It uses 2.7 Watts measured on the AC side. You can turn it on only when your computer is on so, compared with the computer; the power usage of this special modem is pretty insignificant.
LCD computer monitors on an inverter system
My computer is a AMD 1300 Mhz with 128Mb RAM, 20 Gig ATA 100 hard drive, CD burner, and 56K built in modem with a 15-inch LCD monitor.
I measured the wattage with an Emu meter at 101 Watts and 105.4 Watts on a Spar meter on the AC side with everything on. Taking a bit of an average gives 103 Watts of which 19 Watts is consumed by the LCD monitor.
On the DC side of my Selectronic SE22 inverter, the current was measured at 5.0 Amps @ 25.4 Volts (about 127 Watts), which gives an efficiency of about 81% (when nothing else is being run off the 1600W inverter).
Interestingly, turning the monitor off made no difference to the power consumption as measured on the DC side. I assume this is because the inverter became more efficient with the extra load. If the computer system is run with an 800W resistive load also on the inverter, the computer system still use 5 amps @ 25.4 volts with everything on, but this reduced to 4.0 amps when the LCD monitor is turned off.
Forgetting this anomaly, I would say that using an LCD monitor over an older conventional one saves about 50 Watts. In a grid connected 'office' situation - 8 hours/day, 250 days a year, the saving in power would be in the order of 50 x 8 x 250 = 100kWh or about a saving of $12 per year. In a solar situation, with your computer on 8 hours per day, you should save about 400Wh per day, which would be a saving of about one 120 Watt panel. This depends of course on your solar insolation, seasonal variations etc.
Computer printers and inverters
Computer printers come in three main types; dot matrix, laser and ink/bubble jet.
The dot matrix type are rather obsolete now for most applications except for continuous sheet type printing. Our large, wide carriage unit is rated at 120W on the compliance label. Smaller A4 size ones are rated around 60W.
Laser printers are the most expensive and power hungry of the lot. Our small Xerox AP5 unit (5 pages/minute) is rated at 480W. It uses around 0.41kWh/day when left on standby for eight hours a day and printing about fifty pages a day. Our large Mita Vi 230 laser printer/photocopier (23 pages/minute) is rated at 1000W. On a typical eight hour day it uses 1.2kWh/day to print around 260 pages. Laser printers require a good quality sine wave inverter with a good surge ability. The above power consumptions are measured on the AC side.
We recently ran some power tests on our Minolta QMS Magicolour Laser Printer. This is a full colour laser printer that retails for a little over AUD$1100. The compliance label suggests it uses 7 amps (1600 Watts). We'd suggest that this is really a surge rating. We recorded the following readings (measured on 240 Volt AC grid). The warm up took 800W for 30 seconds and then 580W for 1 minute. The printer then goes into a standby mode, using 14-15W. While printing a full colour page, the power changed about every second from 15W to 800W for 30 seconds. After about 30 minutes of not using it, the printer goes into a Power Saving Mode using 6.3 to 7 Watts; however every minute or so it does a 1-2 second surge up to 750 Watts. To conclude, we'd suggest that the Printer tends to use less power than its label suggests. On a Renewable Energy system, we'd suggest you try and do all your printing at once, rather than leaving the Printer on standby for several hours.
In recent times, the ink/bubble jet printers have taken over the 'home' market. I recently purchased a small Canon BJC-1000SP bubble jet for the princely sum of AUD$119. While on standby, I could not detect any power consumption; when printing it used a maximum of 25W (about 20W average). This power consumption was measured on the DC side of my SE22 inverter (whilst the computer was on). I'd suggest that for the average home user printing a few pages a day this power consumption is negligible.
The Dell Desktop Pentium 4 use a fair bit of power. The Dimension E310 model uses between 71 & 132Watts while the Dimension E510 uses 106 - 165 Watts. The Apple iMac G5 with a 20" LCD monitor uses about 100 Watts and can peak up to 120W while opening large files.
I just discovered your January 2004 newsletter, which mentioned the "PEOPLE FIRST NETWORK" in the Solomons. I don't know if you're still looking for printers, but I'm putting together a computer lab for a remote Fijian island (Vanua Balavu), and I've found that HP Deskjet 340 printers are a good choice. They need 10.6VDC, and the ink cartridges are fairly big (I don't know yet how many pages you'd get from them). Admittedly they're a little long in the tooth now, but it's still possible to find little-used ones on E-Bay and suchlike.
Ben Berry |
