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How Much Power Do You Need ?

To determine the maximum output watts and the watt hours we need from our Power Station we first must decide which appliances we want it to power and for how many hours we want to power each appliance every day.  

Inverter: The Inverter takes 12 V D/C voltage from the battery and converts it to 110-120 volts A/C (Alternating Current). This is the maxium output current at the electric receptacles. The wattage rating of the inverter determines which appliances can be powered by this inverter. If my inverter is rated at 1500 watts it will power my 1200 watt toaster oven. But for how long? That depends on the storage battery.

Battery: The battery stores electricity in the form of 12 volts D/C (direct current). Batteries are rated in amps, or amp hours. To convert the amps to watts, simply multiply the amps X volts. A 100 amp hour 12 volt battery would be 12 X 100 = 1200. A 200 amp-hour battery would be 2400 watts. This is the watt hours. The battery storage capacity determines how many hours appliances can be powered. If we have a 100 Ah (Amp Hour) battery which is a 1200 watt hour battery we can power the 1200 watt toaster oven for one hour. If we have a 600 watt hour battery we can power the 1200 watt toaster oven for 1/2 hour. After which the battery will be flat and must be recharged.

 


When we decide which appliances we will power with our power station we need to find the wattage rating of each appliance. To do this find the tag on the appliance that gives the electrical specs. It is usually on the back or bottom of the device, or near the cord. The tag on my refrigerator was inside.

This one is easy. As you can see this tag says 900W (900 Watts). This appliance uses 900 watts per hour.

This tag does not give us the number of watts this appliance uses, but it does give us the volts (120 V) and amps (10 A).

To find watts simply multiply volts X amps. 120 X 10 = 1200 watts. This appliance uses 1200 watts per hour


How much wattage does a refrigerator use?

The best way to calculate the energy usage of a refrigerator is by getting the yearly energy usage from the yellow tag that came stuck to your refrigerator when you purchased it. If you didn’t keep it, you may be able to find it online by searching your make and model. That is how I found mine.

As you can see the yellow tag says this refrigerator uses 416kWh (kilowatt hours) of electricity per year. To determine how many watts it uses in a day, divide 416kWh by 365 days = 1.14 kWh. A kilowatt hour is 1000 watts, so multiply 1.14 x 1000 = 1140. This refrigerator will use around 1140 watts a day. I would round this number up to 1200 watts.

  • Under the APPLIANCE column: list the appliances you plan to use each day.
  • Under the WATTS column  : write the wattage rating for each appliance.
  • Under the HOURS column: write how many hours or fraction of an hour the appliance will run each day. A refrigerator will cycle on and off throughout the day, so write down how many hours a day it will normally run. NOTE: Not all refrigerators are as efficient as this one.
  • Under the WATT HOURS column: Multiply the watts X hours  to get the watt hours. Write that number here.
  • Add all the numbers in the watts column. In this case it is 1560 watts. This is the number of watts needed at the electrical outlet. This is the maxium wattage rating of the appliances we wish to power.
  • Add all the numbers in the watt hour column. In this case it is 2430 watt hours. This is the minimum size of the storage battery to get through a day using the listed appliances.. Unless you plan to use a gas powered electric generator to charge the battery on cloudy days I would suggest at least a 4800 watt (400 amp) battery.