Estimating your Power Demands

Convert Watts to Amps

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You need to have a good idea of how much electricity is required before you can decide on the appropriate size of your solar panel array, and the size of cables and battery bank.

There are three simple steps to determine the average daily load:

  1. Select which lights and appliances will be used.
  2. Find out how many amps or watts each consumes.
  3. Work out how many hours each day (on average) each appliance will be used.

Since the size of your battery bank is rated in terms of amp-hours and the meter on your distribution/meter box measures the power coming in from your charging system in amps, it makes sense to convert watts to amps. I will give you some examples:

  • You have a 12 volt portable radio and cassette player that has a label on the back that says 12 volts, 0.2 amps. You don't need to calculate anything for this as the current draw is already given in amps at 12 volts.
  • You want to use a 12 volt 20 watt light bulb. To work out the amps you just divide 20 watts by 12 volts and you get 1.67 amps.
  • You have a 230 volt juice extractor rated at 300 watts. If you have a solid state inverter rated at 400 watts you can expect 85% efficiency. So to work out the amps at 12 volts you divide 300 watts by 12 volts and you get 25 amps; on top of that you have the inverter efficiency to add to that figure. Divide 25 by 0.85 (85%) and you get about 30 amps.
  • You have a 230 volt colour TV that doesn't have a watts rating but does give an amps rating. The figures it gives are 230 volts, 50 hertz, 0.3 amps. This amps usage figure is the power consumption at 230 volts. Since amps times volts equals watts, this works out at 69 watts (230 times 0.3). Now to work out the amps at 12 volts you divide 69 watts by 12 volts and you get 5.75 amps. If you run this off the same 400 watt inverter you can only expect 70% efficiency (refer to inverter data supplied by your dealer). Divide 5.75 amps by 0.7 (70%) and you get 8.2 amps.

Determine the Average Daily Load

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Now to give you an example of working out the daily power consumption:

  • You listen to either the radio or cassette player for 6 hours each day. The 12 volt system you have is rated at 0.2 amps at 12 volts. Multiply the amps by the hours and you get the result of 1.2 amp-hours per day.
  • You use three 20 watt 12 volt lights for about four hours each night. The power consumption for each light we worked out earlier to be 1.67 amps. So for three lights we calculate a current draw of 5 amps. So to calculate the power consumption we multiply 5 amps by 4 hours to get the result of 20 amp-hours per day.
  • You use a juice extractor for 10 minutes each day. We have already calculated that the inverter draws 30 amps when the juice extractor is running. Divide 30 by 6 (because you use the juicer for 1/6th of an hour) and you get a result of about 5 amp-hours per day.
  • You watch the colour TV for about 2 hours each night. We estimated before that the inverter draws about 8.5 amps when the colour TV is on. Multiply 8.5 by 2 and you get 17 amp-hours per day.

Here are those figures in tabulated form:

ApplianceAmpsHours UsedAmp-hours
radio/cassette 0.20 6.00 1.20
3 lights 5.00 4.00 20.00
juicer 30.00 0.17 5.00
colour TV 8.50 2.00 17.00
TOTAL 43.20

We can design your system for you, using a computer based Power System designing software. We will require detailed information on your envisaged power usage including power ratings and hours per day usage of lights, appliances etc. Please fill in and submit a quote request for a residential solar system or download a Power System Sizing form.

Typical Appliances Ratings A-F

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POWER CONSUMPTION GUIDE (230V)
APPLIANCES START WATTS
Air Conditioner
(Single Split System)
(evaporative - mobile)

-

500 - 2500
275 - 1000
Alarm/security system - 6
Blanket (under) - 60 - 120
Blanket (over) - 150 - 350
Can Opener - 100
Cassette (Tape) Player Deck - 30
CB (receiving) - 10
CD Player - 30
Circular Saw (small) - 1350
Clothes Drier - 2400
Coffee Grinder - 75
Coffee Maker - 300-1500
Cordless phone (use or charge) - 2-3
Computer (Laptop or Notebook) - 40-60
Computer (Desktop + Screen)
office use
gaming
-
150-200
500-1000
Computer Printer - 30-50
Digital Video Recorder - 20-50
Disposal Unit - 650
Drill - 250 - 500
Dishwasher - 1200 - 2500
Domestic Water Pump 2000 500
Electric Toothbrush (charging stand) - 6
Exhaust Fan - 40 - 75
Fan - 20 - 100
Fax (standby) - 10
Fax (printing) - 120
Food Mixer & Whiz - 500
Floor Polisher - 350
Freezer 2500 500
Frypan - 1400

NOTE: These figures are a guide only and the wattage ratings may vary greatly from one appliance to another.

Typical Appliances Ratings G-Z

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POWER CONSUMPTION GUIDE (230V)
APPLIANCES START WATTS
Hair Dryer, heated - 800 - 1800
Heater - 500 - 2400
Hotwater Service - 2500 - 5000
Infra-red Grill - 2000
Iron - 800-2000
Juicer/Blender - 350-550
Kettle or Jug - 1600 - 2400
Lighting LED - 3-15
Lighting Fluoro - 10-20
Microwave oven - 600 - 1800
Mobile phone (charging) - 5-15
Modem/Router - 5-15
Modem NBN Satellite - 35
Radio - 15 - 60
Radiator - 1000 - 2500
Record Player - 75
Refrigerator 1500 300
Sewing Machine - 60
Space Heater - 2000
Stove - 5000 - 10000
Tablet (charging) - 10-25
Television LED - 30 - 120
Toaster - 500 - 1500
Vacuum Cleaner - 700 - 1800
Washing Machine 2500 600
Welder - 140A - 4000

NOTE: These figures are a guide only and the wattage ratings may vary greatly from one appliance to another.

Electric Motors

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Electric Motors - Starting Current
- Type of Motor
- Watts Induction Capacitor Split-Phase
1/6 hp 275 600 850 2050
1/4 hp 400 850 1050 2400
1/3 hp 450 975 1350 2700
1/2 hp 600 1300 1800 3600
1 hp 1100 1900 2600 -

NOTE: Brush type motors without a load do not require a significantly higher starting current than their continuous current rating.

Read all about the power requirements of various appliances run from an inverter. There are articles about the power needs of TV's, sound equipment, bread ovens, computers, washing machines, pumps, printers, fans etc.


We install solar systems in Northern NSW and Southern QLD.


QLD:
Gold Coast (from Coolangatta to Southport), Nerang and Hinterland (Beaudesert) and out West (Warwick, Stanthorpe, Killarney)


NSW:
Northern NSW (Tweed Heads to Yamba, including Evans Head, Byron Bay and Ballina); the Far North Coast Hinterland (Grafton via Lismore to Murwillumbah) and out West (Casino to Tenterfield, including Drake and Tabulam, as well as Woodenbong and Bonalbo)

For larger system we also go up to Brisbane or down to Coffs Harbour and even Glen Innes. Other places by arrangement.