I live in the country, several miles at least from the nearest municipal water lines. Therefore, I have a well for water, with an electric pump. And that means I need power to get the water out of the ground. If the power fails I need a backup source of power to run this well pump if I want to have any water.

What I have is a variable speed, constant pressure well pump, a Grundfos SQE pump. One of the nice things about this well pump compared to conventional well pumps is that it has a very low startup surge because the controller gradually ramps up the speed, and it only runs as fast as needed to maintain pressure.

Conventional well pumps have a huge startup surge and then they run at full speed, so you pretty much need a gas generator to run them.

With one faucet running I measured it's power consumption at about 900 watts.

I decided to try running it off of a 12V, 1500W inverter.

The well pump is a 240V pump but my inverter is a 120V inverter. Yes, I know 240V inverters are available, but they are not common and they are expensive in the USA.

So I went on Ebay and found a used 2kVA transformer of the type normally used to step 480V down to 120/240V. I think it was around $50 shipped. I think it was an Acme Electric transformer, but Square D and others make these too. They are very very common, and used ones are cheap and plentiful.

I wired the transformer so that it stepped my 120V up to 240V -- 120V into the secondary (ignore the center tap) and 240V comes out on the primary.

I connected my well pump to it and powered on the inverter, which for testing purposes I had connected to a deep-cycle marine battery.

The well pump controller showed that the power is on and no error lights.

Turned on a faucet and I got water and the well pump controller showed that the pump is running.

Now at 900 watts even a 110 amp hour deep-cycle marine battery likely won't last much longer than 10 minutes, but in 10 minutes you can pull quite a few gallons of water out of the ground. And I can connect the inverter to my car's battery and run the engine to keep it charged OR set up my 300W of solar panels and charge controller to keep the deep-cycle marine battery charged.