What size inverter do I need?
If you’re looking at running some 240V appliances from a 12V battery system, you need an inverter. The question that you need to ask though, is what size inverter do I need? Get it right, along with the rest of the system and you’ll be able to happily run the appliances you need with no ill effects. Get it wrong though, and you can damage your batteries, cause a fire, flatten your batteries or have all sorts of unpleasant experiences.
What is an inverter?
Put simply, an inverter is a piece of electrical equipment that takes 12V power, and converts it to 240V, or the same as what you’d have at home. It’s important to know that this is more than enough to kill you, and you should be at least as respectful with an inverter as you would be at home with a power point.
Sizing an inverter
In order to pick the right size inverter, you need to look at the specifications of the appliances that you want to run, and add a bit of a margin in for peak power draw.
Every single electrical appliance you have at home will have a sticker on it, or a label on the cord that will cover the amount of power consumed. Here’s a few examples
A toaster uses between 700 and 1200W
A kettle uses between 1600 and 2200W
A heat gun uses around 300W
A soldering iron uses around 40W
An induction cooktop uses between 200 and 2000W
Once you know what appliances you want to run, you can size your inverter accordingly. I’d go with 30% extra above the rating (2200W appliance to take a 2860W inverter), and then you have the right size inverter.
Its not just about inverter size
However, just before you rush off and place an order on a fancy, big inverter, you need to know this is only part of the equation. Fitting a big inverter to a battery system that was never designed to pull so much current is a recipe for destroying your battery very quickly, and best case dramatically shortening its lifespan.
Lead acid batteries in particular are not designed for heavy loads, and whilst you might get away with running a big inverter and some appliances short term, its going to kill your battery eventually, in a much shorter time frame than it could have been.
What ever battery system you have, you need to look at the maximum discharge specifications, and make sure its suitable for the inverter size. When you buy Renogy gear, it specifically tells you what size and type of battery you need to run high wattage appliances. Under 200aH of lithium is not suitable for more than 2000W appliances, and doing it can damage the battery.
Beyond this, make sure your cabling and fuses are suitable for the setup too; I can’t stress how much heat is generated when you are pulling high current from your batteries, and if its not set up well you’ll end up with smoke at best, and a fire at worst.
What do we run?
In our Dmax, we have a 230aH DIY lithium battery, running a 2000W Renogy inverter, plus our fridge, lights and other random bits and pieces. We use the inverter for charging camera batteries, laptops, Ryobi batteries and running our induction cooktop as required. The BMS in our battery is good for 150A, which is around 1800W, and I make sure our induction cooktop doesn’t exceed this as its not worth the damage.
Our Reconn R2 has two 170aH Renogy lithium batteries, connected to a 3000W inverter. Again, this is used for charging laptops, running our induction cooktop and also a toaster that gets used often.
However, prior to this we had a 300W, and 400W inverter that did everything I needed it to; camera batteries, drone batteries, laptop charging, Ryobi 18V battery charging and your basic, low electrical draw appliances.
If you are looking at an inverter, make sure you get one that suits the appliances you want to run, and your battery system. If a compromise needs to be made, do so; don’t damage your battery system just to run thirsty appliances!
What do you run with an inverter?
