Power Inverters

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How do I know what size inverter I need?

Once you decide on the type of inverter you need, either Pure or Modified Sine Wave, then the next step is to calculate the size you need. This is the easy step; it is nothing more than simple maths. As an example, say your Laptop uses 150 watts and your portable printer uses 200 watts, simply add them together for a total of 350 watts, assuming that both appliances will be running at he same time. So a 350 watt inverter should do the job, but we recommend adding 25% to your total working load for safe operating margin.
If you don’t know the power consumption of your devices refer to the operating handbook which should have a specification table, otherwise contact the manufacturer.

When adding the power consumption of your devices keep in mind that the continuous power consumption of the device is when the device is running normally and peak power is when a device, such as a motor starts up and has a surge to get running before it settles into a continuous load. This is an example of when it pays to purchase a larger than needed inverter.

It is important to understand that there is no way to modify or clean up the power output of a modified sine wave inverter. If you have trouble with an appliance not working properly then the only solution is to purchase a pure sine wave inverter.
While a pure sine wave inverter is more expensive you can guarantee that whatever you plug into it will work, relative to the inverters capacity.

The length of time you can operate an inverter depends on the amp-hour capacity of your battery.

Please consider the following example;

The formula for power is: P = VI
Where:
P = power in watts
V = voltage
I = current in amps

Therefore transposing the formula we can determine the current drawn from the battery at a given load.

I = P/V

So say you have a 1000W pure sine wave inverter in your motor home, and assuming it is running at full load;

I = 1000watts/12volts = 83.33amps.

As you can see from the example above the battery will not last long if it has this much load on it without the engine running to keep it charging.

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