Anyone used an inverter as a mains backup?

[NigelJK]

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

[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.

[DeadEyedJacks]

Tesla do Solar Roof and Battery package.

Tesla Solar Roof | Tesla UK

Also have decent sized car batteries...

[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.

[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.

[AtW]

I say take off and nuke whole site from orbit - it’s the only way to be sure that lack of mains power is no longer a problem there...

[Lost It]

If you have the engine running in the car, the "duty cycle" will last a bit longer... Not fuel efficient though.

[Paddy]

Live out in the sticks and get occasional power cuts. Got an old generator but it's on its last legs.

Wondering if a viable alternative would be to hook up an inverter to the battery in the car.

Anyone tried this?

A car battery is not much use as it’s for short bursts of high demand. You know like for staring a car.
A leisure battery from a caravan is more use.

Or why not buy a bloody UPS as that’s both a battery and an inverter? As well as the electronics to provide a constant supply during the failure rather than you having to go and rewire everything.

That way you’ll have enough light to bleed the radiators at the same time.

I have tried this with a car battery and it only lasts a couple of hours due to the fact that the inverter will cut out when the voltage drops just below 12v. I have a new setup with a leisure battery and a smart charger. I can get six hours run-time out of it.

I would definitely recommend a smart charger even for a car battery.

At my villa in southern Europe, the power is cut many times due to the high number of thunder storms in the mountains. Therefore, I also have a standby generator with electric start. I can run most thing from that.

UPSs don't really last for several hours.

[Lance]

This post got me looking up generators on Amazon. For some reason Amazon.de seems to offer many more attractive options than co.uk site. No idea. Anyways, loads of options. They've certainly changed since me dad's day.

Gas Turbines - Products | Solar Turbines

A few years ago I did some sums on whether I could generate my own electricity using a gas turbine.
Fuelled with LPG.

It was cheaper than buying from the grid (that includes purchase and fuel as well as maintenance for 10 years).
The real benefit at the time was if you had a solar panel and got subsidies. My plan was to use the turbine to feed power back to the grid and clean up at around 40p/kWhr.

Only problem is that they are noisy.

[Lance]

Live out in the sticks and get occasional power cuts. Got an old generator but it's on its last legs.

Wondering if a viable alternative would be to hook up an inverter to the battery in the car.

Anyone tried this?

A car battery is not much use as it’s for short bursts of high demand. You know like for staring a car.
A leisure battery from a caravan is more use.

Or why not buy a bloody UPS as that’s both a battery and an inverter? As well as the electronics to provide a constant supply during the failure rather than you having to go and rewire everything.

That way you’ll have enough light to bleed the radiators at the same time.

[NigelJK]

To do it properly have a look at what is done in Narrow boats. You'll need a residential battery pack and a good quality inverter. We have 5 residential batteries and an 1800W inverter. It possible to then use a battery conditioner, possibly solar (again use the proper thing, not a car one) to keep them topped up.

[scooterscot]

This post got me looking up generators on Amazon. For some reason Amazon.de seems to offer many more attractive options than co.uk site. No idea. Anyways, loads of options. They've certainly changed since me dad's day.

[vwdan]

Mains backup for what, precisely? Certainly possible to use a 12v battery and inverter - that's essentially what UPS's are, but you need to define your use case very carefully.

If you're imagining keeping your whole house running, then you're going to need a lot more than one 12v battery and some serious gear

[AtW]

You are a contractor, right?

Hook the house up to your Lambo battery.

Sorteed.

[stonehenge]

Live out in the sticks and get occasional power cuts. Got an old generator but it's on its last legs.

Wondering if a viable alternative would be to hook up an inverter to the battery in the car.

Anyone tried this?