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INVERTER

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INVERTER

All appliances use power and the power usage of these appliances will determine how the rest of the system will be designed to ensure that enough power is available to run them.

First, calculate your daily (24-hour) average power consumption for all of the electrical loads you place on your system. List all of the appliances and their amp draws. If amps are not listed on the appliance, you can figure amps with the following formula:

Amps = Watts divided by Volts

For converting 240V appliance Watt rating to a DC amp rating when running through an inverter (inverters convert either 12 or 24 DC volts to 240V AC so an AC powered appliance can be run off a battery bank) use the following formulas

12 Volt DC Amps = AC Watts divided by 10

24 Volt DC Amps = AC Watts divided by 20

An example: A 1500W electric kettle running through an inverter of a 12 Volt battery bank:

1500W divided by 10 = 150amp draw per hour at 12 Volts

As you can see running high wattage AC appliances through an inverter results in very high power consumption. This is not really too much of a problem with fast appliances such as Microwaves, toasters and fast kettles as there run time is generally less than 15 minutes. So actual power consumption for a 5 minute boil time for the kettle in the above scenario would use the following amount of power:

150amps divided by 12 (Time, 5 Minutes goes into 60 Min 12 Times) = 12.5 Amp Hours (Ah) consumed from our 12 Volt Battery Bank

However continuous running for 30 minutes of say a 2000w BBQ would result in a flat battery very quickly, even with a large battery bank.

2000W divided by 10 = 200amp draw per hour at 12 Volts

200amps X 0.5 (Time, 0.5 = ½ hour) = 150 Amp Hours consumed from our 12 volt Battery bank

Next, estimate the normal daily usage for each in hours, so that you have a list of appliances and their daily draw in amp-hours (Ah). Now total them all up. You should have something that looks like the example (This is just an example to demonstrate the point) chart below which would be close to an average 40ft powerboat with 4 people on board not trying to be energy conscious.

Sample Appliance Load Chart

For a 40ft Power Boat with 4 People on Board

12-Volt DC Loads

Appliance

Avg. current draw (amps) at 12-Volts

Avg. use
(hours/day)

Avg. 12-Volt consumption
(amp-hours/day)

LCD TV

4

8.0

32.0

GPS

2.0

3.0

6.0

Stereo

4.0

0.5

2.0

Anchor light (LED)

0.2

12

2.4

20 x LED Cabin Lights

8.0

6

48

VHF

receive

0.5

4

2.0

transmit

5.0

0.4

2.0

Toilet, Shower & Pressure pump

5.0

3.0

15.0

Bilge pump

5.0

0.5

2.5

Modest-size refrigeration

5.0

18

90

DC Total Ah

 

 

201.90

 

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