Anyone used an inverter as a mains backup?

[stonehenge]

Thanks for all the replies.

Mostly, I'd just need the backup for low wattage appliances eg. low energy light bulbs, laptop, TV etc. If the mains was down for an extended period, I'd need to power up the fridge/freezer occasionally.

We're on private water (borehole), so ideally I'd like to be able to run the pump occasionally to recharge the pressure vessel. However, the pump is 3 amps (750w), and probably a heck of a lot more amps on start-up.

The car alternator is rated at 120 amps. I don't know if it's true or not, but I read somewhere that they put out about half the amps at idle speed.

[RSoles]

I wouldn't do it.
As others have said a car battery is designed for shallow cycling, the alternator keeping it topped up most of the time.
Letting it run down will kill it quickly.
Then you're out in the sticks, no power, no car, somebody needs medical attention....

The fridges and pump are inductive loads, which may blow the crap out of an underpowered invertor.

By the time you've bought a decent invertor and deep-cycle battery, you're in the budget range for a new generator.

I live out in the sticks and run a generator (2.5kW IRRC), works perfectly, every time I drag it out, plug it in and start it, the power comes back on.....


BTW, It's extremely important to have some interlock so that you don't have mains power and the secondary connected together.

Maybe look into a solar power setup? This would provide the batteries, invertor, interlock all in one package.

[DeadEyedJacks]

Tesla do Solar Roof and Battery package.

Tesla Solar Roof | Tesla UK

Also have decent sized car batteries...

[stonehenge]

I wouldn't do it.
As others have said a car battery is designed for shallow cycling, the alternator keeping it topped up most of the time.
Letting it run down will kill it quickly.
Then you're out in the sticks, no power, no car, somebody needs medical attention....

The fridges and pump are inductive loads, which may blow the crap out of an underpowered invertor.

By the time you've bought a decent invertor and deep-cycle battery, you're in the budget range for a new generator.

I live out in the sticks and run a generator (2.5kW IRRC), works perfectly, every time I drag it out, plug it in and start it, the power comes back on.....


BTW, It's extremely important to have some interlock so that you don't have mains power and the secondary connected together.

Maybe look into a solar power setup? This would provide the batteries, invertor, interlock all in one package.

Thanks, and I've reached the same conclusion. Also read that the cheap modified sine wave inverters could damage electric motors. Certainly don't want to risk knackering the water pump. Once you get into the realm of multi-kw pure sine wave ones, they're more expensive than generators.

New generator it is then.

[NigelJK]

We use a 12V fridge on the boat. All pumps (including the bilge) are also 12V.