Choosing the correct size Inverter

You can’t just buy any size inverter, you need to choose the right size inverter for your setup.

Step 1: Match The Inverter To The Load

Add up the total wattage from each of your appliances that you want to run at the same time.

Think about your average day – which appliances will you run simultaneously?

More important than their total watts is their initial start-up needs, their peak watts (start-up watts). Anything with a pump, compressor or motor will have a higher peak power draw, that will drop off after a couple of seconds.

It may only be for a short time, but your inverter still needs to be capable of handling the peak load. If it can’t, the protection system will shut down the inverter, or in the case of a cheap inverter it could cause damage.

Another easy way to mitigate this is to stagger when you turn on appliances. In other words, don’t switch them all on at the same time!

To give you an example, let’s say you want to make a cup of coffee. When you first turn your coffee machine on it draws around 1300-1800 Watts (depending on your machine). It then drops down to almost nothing between cups.

Then when you go to make another cup the power draw spikes back up to around 1300-1800 Watts. Now this is adequate enough if you are only going to run your coffee machine and nothing else.

But if you also want to make breakfast and run other appliances at the same time then you will need a larger inverter.

Step 2: Ensure Your Battery Bank Can Power The Inverter

So, you’ve sized up your load requirements. Now you need to make sure your battery bank is large enough to power the inverter.

We recommend for every 100Ah of deep cycle battery, you can power a 1000W DC to AC Inverter. Be wary of cheap lithium batteries, they are unable to meet the standards set by leading quality brands of batteries with trusted specifications.

Step 3: Consider How Long You Plan To Run These Appliances

A reputable battery manufacturer will display how long their battery can produce its maximum Amp output. It’s one thing to say you have a 100Ah Lithium Battery, but it is another to advertise that you can pump out 100A consistently for 1 hour.

If your laptop charger draws 50W continuously while plugged into the inverter, this equates to approximately 4 Amps at 12 Volts. So theoretically, you could run the laptop for around 24 hours continuously on a 100AH Battery

Keep in mind, you need to consider power draw of the inverter itself. A 1000W inverter will roughly draw around 1 Amp per hour even without any load applied. So, it’s best to factor this in to your calculations.


Got a Larger Battery Bank/Solar System?

Look to an inverter charger.

The pioneer of inverter chargers is Victron with their PowerAssist feature. This allows you to use some power from AC input (mains power or generator) and some power from your battery system via the DC to AC inverter.

This is particularly handy when running an air conditioner. You can use a small inverter generator coupled with your inverter charger to run your AC or heat pump. Great for those hot summer nights!