LCD computer monitors on an inverter

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.

Printers

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.

Desktop Computer

The Dell Desktop Pentium 4 use a fair bit of power. The Dimension E310 model uses between 71 & 132 watts 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.

We found that most desktop computers will use around 120-140 watts before inverter losses. This depends a bit on the size and type of monitor and how hard the computer is working. Newer desktops with the faster or dual processors may average out to about 200W, unless you have a LCD monitor.

Laptops & Tablets

Laptop computers are becoming a lot cheaper and are a good choice for those wishing to run a computer for extended periods on a solar system. I can now give you several laptop power consumptions thanks to Rob, Dave and Ernie from the Yahoo Discussion Group called '12VDC_Power', and to Peter Pedals and Chris Nuss from our staff.

1. Sony laptop 3 years old: 28 watts (W)
2. Dell Inspiron 600M, 40GB drive, 512 MB Ram; 14.5 inch display: 23-25 watts (40-53W if charging the internal battery). A Dell Inspiron 1150, using an auto adapter supplied by Dell, used 1.75A at idle and 2.95A playing a DVD at 12.6 volts. This computer has a 2.8GHz P4, 1GB RAM, 60GB hard drive, with a DVD burner.
3. IBM Think Pad: 30 watts
4. Toshiba: 25 watts
5. Mac 1 Book 2001: 30 watts
6. Compaq Presario 700, 20GB drive, 14.5 inch monitor: 28 watts when running; 40-60 watts booting up and shutting down; 2.3 watts on standby.
7. 17" PowerMac uses just 23 watts, with the CD burner running and a test program doing continuous disk seeks, listening to iTunes, while downloading over wireless networking!
8. 10" MSI Wind = 15W
9. 12" Apple G4 Powerbook = 20W
10. 15" MacBook = 25-30W
11. 15" Toshiba = 30-35W

Most of the above lap tops are a year or two old and it is possible that newer and more powerful lap tops may use more power- eg 50 watts. We suggest that if your solar power supply is limited, you stick with a lower 'power' unit unless you do a lot of graphics or video editing etc.

From this list of measured laptop computer power consumptions, I'd suggest 25-30W is the average range. These power consumptions are measured on the AC side (eg, they do not include inverter losses).

A small number of laptops are designed to work direct off a 12 volt battery. The vast majority run from 14-20 volts DC.

Generally there are two options to run your laptop from your solar system – an inverter (such as our 200W Victron Inverter ) or from a DC-DC voltage up-converter. While we have not extensively tested these two options, it is our feeling that the up-converter would be in the order of 15% more efficient than a small inverter. Running the laptop on its own on a large house inverter may not be very efficient.

To conclude, we'd suggest that a laptop computer would use around 30W off the DC power supply, and say 40-50W after inverter losses. An 80 watt solar panel should easily run a laptop computer all day in say the Brisbane area. The same solar panel will, on average, only run the desktop computer for a 1-2 hours. So if you are planning on using a computer for say 8 hours a day on a solar system, a laptop could save you purchasing about three to four 80 watt solar panels, 300Ah of increased battery storage, and a larger inverter!

14" iBook

The power required to run this laptop in some modes is surprisingly high. The VA readings indicate the power supply ties up a lot more available power than what might seem typical of a quality laptop computer. The figures were, however, measured while the computer was in 'sleep' mode, not while the computer was in use, and the power supply is designed to charge the batteries as fast as possible in this state.

Figures for power consumption while in sleep mode (at 100% battery capacity) were reasonable, and the option of adjusting the processor rate in the 'energy saver' menu of 'system preferences' meant that further adjustments could be made to suit the use of the computer, and further reduce power consumption.

Computer in sleep mode and chargingMinutesSOC %WattsVA0264169103441692041416930504169.5405841.470506640.971.160743766.5708030.556.4808526.548.99089.521.642.310093173511096132612010010.522Computer in sleep mode @ 100% SOCWattage2.7VA11Computer in Hi performance use @ 100% SOCWattage25VA55Computer in Lo performance use @ 100% SOCWattage24VA50