Power Consumption of Cooling Fans

The past summer here has been a hot one with summer temperatures 33 - 38C for several weeks. This has led me to try a number of fans to keep cool.

See our range of fans

a) 12 & 24V MINI EXTRACTOR FANS: These are small 120mm fans similar to cooling fans on desk top computer cabinets. They use around 6W and are effective within about 1m. They are rated to move 2 to 3 cubic metres of air per minute. If you really need to economise on your power usage, they are the smallest fans available. My main criticism of them is that I have found them quite noisy, (it makes more noise than a 30W 230V type of fan).

b) DC AUTOMOTIVE FAN: These are generally made as accessories for the automotive market - commonly they are available in 12V and in 24V from specialist sources. They are around 150 - 180mm and draw 12-24 watts. They make more noise than a 230V fan.

c) CEILING FAN - 230V: All 230V type fans should be run from a sine wave inverter. They are typically rated at 60-80W. When run alone on a 1600W SE22 Selectronic Inverter, it used 53, 66 and 73 watts on slow, medium and high speed. This is remarkably efficient running alone off a large inverter. The same fan when run while the TV was on drew 21, 38 and 48 watts. This power consumption is measured on the DC side of the inverter. In terms of cooling a room, a conventional ceiling fan would be my first choice, though they do tend to blow the hot ceiling air down on you.

d) SMALL TABLE FAN - 230V: This is a 23cm table fan with a 30W rating. Running on the SE22 Selectronic Inverter with no other load, it drew 38 and 41 watts on slow and fast speed. When run on the same inverter with the TV on, it drew 13 and 15 watts. I find this fan very good when placed 2-3m away. It is very quiet and ideal as a bed fan!

e) LARGE PEDESTAL FAN - 230V: This is a large 40cm fan rated at 55W. When run with no other loads on the 1600W Selectronic inverter, it drew 63, 66 and 71 Watts on slow, medium and fast speed. When run while the TV is on, it drew 38, 41 and 45 watts.

CONCLUSIONS: I found both DC fans (mini and automotive) to be quite noisy, especially at night. However, they do use less power than a 230V one with no other load on the inverter.

The closer you place the fan to you, the more effective it is and therefore you can run it at a slower speed (or use a smaller fan). While this sounds rather obvious, the effect of distance is very marked. Try and work out first where you can place the fan to be close to you - then you can choose between a table, wall mounted or pedestal type.

I also ran all 3 fans at once to simulate what might occur in a home with a few bedrooms. The rating on the labels of the ceiling, pedestal and table fan added up to total of 155 watts.

When all 3 fans were run on the inverter with no other load, the power consumption was 81, 105 and 150 watts on slow, medium and high speeds. When run with the television on, the power consumption totalled 77, 85 and 107 watts.

All 230V fans appear to be an efficient load for an inverter and seem to use less than their rated power if the inverter is running another load at the same time.

Power Consumption of Pressure Pumps

See our range of pumps

The question whether to use a 12/24 volt or a 230 volt pressure pump for a home pressure system is an interesting one.

The advantage of a 12/24 volt pump is that they are smaller and more energy efficient if you only want to run one tap or shower at a time. They typically draw 40 - 80 watts. You don't need an inverter to run them. The disadvantage of these pumps is that they have brushes and require more maintenance than a larger 230V unit.

The 230V pumps are much larger (usually 200 - 800W) and they will run three or more taps at once. They are often cheaper than the 12V type. However, they would use more power and you could be without water if your inverter ever breaks down. You would need quite a large inverter to run the pump. This could add several hundred watts of size to your inverter (when you consider that the pump will probably need to be on while the washing machine etc is on). This could amount to several hundred dollars extra for a larger inverter.

Running 230V Fluoros on an Inverter

Conventional 'straight' fluorescent light globes (often referred to as 'fluoros') have a very poor power factor and are a difficult load for an inverter to run, particularly if these lights are the sole load. We suggest you try to use electronic ballasted PL fluoros as much as possible if these are being run off an inverter (particularly if they are the sole load). These fluoros are sometimes called 'hybrid' or 'U-shaped' fluoros and are industry standard today.

See our range of "fluoros"

• E27 sockets
• Fluoro lamps

Running a CPAP machine on an Inverter

With our ageing population, a condition called Sleep Apnea is becoming more prevalent. A typical symptom is excessive snoring which can be very disturbing to any partners.

CPAP machines (Constant Pressure Air Pump) are sometimes prescribed to alleviate the condition by delivering a constant pressure of air through a hose and mask while you sleep.

Unfortunately, these devices use a reasonable amount of power. We measured the current on the 12V side of a 230V inverter using a Resmed model. It used 5.1 amps when running at 9cm of water pressure. The Wanderer Magazine recently published an article where the current on another unit was measured at 6 amps.

A 5-6 amp current at 12 volts for several hours is a reasonable load - if it is running for say 8 hours each evening, you would need around a 120W panel to keep your battery charged. This would, of course, depend on how much sunshine you were getting in your area.

The good news is that the article's author found a 12 volt model that only uses 1.5 amps which is about a quarter of the power (depending on the setting). They can be purchased through Sleep Easy.

If you want to use one on a Renewable Energy system (perhaps on a mobile home) we suggest you first seek appropriate medical advice. Then you can contact us for advice about how to keep it powered up!

Also read: Powering ResMed/CPAP products with batteries.
A Sullivan III Series CPAP machine at pressure setting of 10cm H20 draws 2.8 amps of current on the 12 volt side of a small inverter.

Heating appliances on an Inverter

The use of these appliances is only possible on large PV systems during periods of surplus power.

Hair Dryer: Most hair dryers use at least 1200W though they usually have a few low settings. A friend found a 400W 'travel' type hair dryer for $8. It has two settings and @ 25V it drew 8 and 17 amps. It is quite effective for drying off on those cold winter evenings. Since one would only use it for a few minutes, it wouldn't use a lot of power.

Electric Blankets: One unit I looked at drew 128W maximum. It had separate left and right 64W heaters each with 4 settings. It is usually recommended that they only be turned on for 15 - 10 minutes before retiring and then turned off.

Bar Heater: While finding it very difficult to find a hair dryer or electric jug under 1200W, I was surprised to find a 750W bar heater at K-Mart! It has 2 bars and so can be run at 375W. It is a pleasant luxury for 5 minutes when you get out of the shower or on a cold winter's morning! I've also seen 1000 and 1200W dual element heaters.

Conclusions: All the appliances mentioned (except the micro wave oven) are known as resistive loads with a unity power factor. This means that they are relatively easy loads for your inverter. If one uses foods and recipes that are relatively quick to cook, a couple of 80W solar modules could supply 1 - 2 people with enough power to cook their meals.

However, before buying such appliances, you should speak to your solar supplier for accurate advice about your personal cooking needs, the average monthly solar insolation to expect in your area, the limitations of your inverter etc. If you need to run a generator to charge your batteries, then you should cook with wood or LP gas!

If you live on the electric utility grid powered by non renewable sources such as coal, then you'd contribute more carbon dioxide greenhouse gases using electricity. According to Choice magazine electric cook tops are more energy efficient than gas because only 40% of the energy produced goes to heat the saucepan and contents, versus 60 - 70% for electricity. However, some two thirds of the energy in coal is lost through its conversion and power transmission to your home. So gas cooking is recommended for those of you on coal fired electricity.

However, if your solar system is producing surplus power (and your inverter is big enough) then buying a few cheap 230V cooking appliances will use up your excess power and lower your fuel bill!