Inverters

[WTFH]

TV is 52W. Table lamp is 7W. Laptop charger is 65W (max) but I'd expect it to draw a lot less than this, especially as the battery would already be fully charged (laptop is always plugged in).

52+7+65 =124, i.e. a lot more than you claimed. You then say that you “expect” it to draw less. And again, you’re assuming 100% efficiency.
Also, your original list included a fridge/freezer and central heating.
Sounds like you know the answer to your question, but are trying to justify a “faulty inverter” instead of poor calculations and assumptions.

If you’re hoping to use your laptop, are you also hoping to access the internet? Would that be tethered over a phone, or using your broadband router? Stick another 10-20W for the router.

If we ignore the fridge/freezer and heating, you’ll want a 200W or more inverter.

Give it a go and tell us how long it lasts.

[DealorNoDeal]

If we ignore the fridge/freezer and heating, you’ll want a 200W or more inverter.

I'll probably substantially over-size it just to be on the safe side eg. 500W.

[DealorNoDeal]

After some "research" it appears that the starting current of a 1kW single phase motor is 3x the run current so you'd need a 3kW inverter just to start the thing.

That sounds about right because the lights in the house momentarily dip when it starts. Similar to switching a kettle on.

I think I can definitely forget any idea of running that off an inverter!

[Protagoras]

Notwithstanding the matters of load, ratings and efficiency, I'd still be wary of using the car as a 'mini power station' as proposed.

It just seems to have too many practical downsides. As previously noted, the battery Ah in the car is likely well below what's required for the application, modern car batteries are often under a cover, etc. I'll add that at idle the alternator voltage is probably lower than normal running, so I'd also be concerned about alternator temperature too.

As mentioned above, a generator would be better. Or perhaps a charger / inverter / battery combination in a dry well ventilated space which would also allow the use of a battery type better suited to the application and could be located closer to the things to be powered.

N.B. For others reading this thread in future may I just note that this discussion is about powering stand-alone things from an inverter with no connection whatsoever between the inverter to the mains wiring installation.

[DealorNoDeal]

It just seems to have too many practical downsides. As previously noted, the battery Ah in the car is likely well below what's required for the application, modern car batteries are often under a cover, etc. I'll add that at idle the alternator voltage is probably lower than normal running, so I'd also be concerned about alternator temperature too.

The load I'm proposing putting on it is about the same as having the car headlights on, so it's not exceptional.

However, whether the alternator will produce enough current at idle speed, to prevent the battery discharging is another matter.

I guess a simple test would be to leave the car running for a few hours with the headlights on and then check the charge level of the battery.

I might get my neighbour down the road to do try it because leaving the car running is how he keeps the battery charged on a car they rarely use. I have suggested (tactfully) that he ought to get a battery charger but he hasn't.

[WTFH]

The load I'm proposing putting on it is about the same as having the car headlights on, so it's not exceptional.

However, whether the alternator will produce enough current at idle speed, to prevent the battery discharging is another matter.

I guess a simple test would be to leave the car running for a few hours with the headlights on and then check the charge level of the battery.

I might get my neighbour down the road to do try it because leaving the car running is how he keeps the battery charged on a car they rarely use. I have suggested (tactfully) that he ought to get a battery charger but he hasn't.

OK, if you're planning to run the engine, then that slightly moves the goalposts.
Then you need to work out how much fuel the car burns when idling, and how much does that increase if a load is put on the alternator. e.g. If your car burns £1 of fuel per hour idling, then your 100W of electricity that you use becomes quite expensive. (£10 per kWh compared with £0.52 per kWh at the current proposed cap)

You might be a bit surprised to know that modern HIDs run at 25W, so 2 of them would be less than your TV.

[Protagoras]

The load I'm proposing putting on it is about the same as having the car headlights on, so it's not exceptional.

However, whether the alternator will produce enough current at idle speed, to prevent the battery discharging is another matter.

I guess a simple test would be to leave the car running for a few hours with the headlights on and then check the charge level of the battery.

I might get my neighbour down the road to do try it because leaving the car running is how he keeps the battery charged on a car they rarely use. I have suggested (tactfully) that he ought to get a battery charger but he hasn't.

Which, of course, also rather depends on the headlight bulb technology in your car (Halogen / Xenon / LED) ...

Diversion from topic, but I'm so glad I don't live next to your neighbour!
As well as causing unnecessary pollution and noise, this is not good for efficient charging, catalytic convertor, DPF (if fitted).

[DealorNoDeal]

Then you need to work out how much fuel the car burns when idling, and how much does that increase if a load is put on the alternator. e.g. If your car burns £1 of fuel per hour idling, then your 100W of electricity that you use becomes quite expensive. (£10 per kWh compared with £0.52 per kWh at the current proposed cap)

Given that it's only for when the power goes down, I'm not too bothered about the running cost.

You might be a bit surprised to know that modern HIDs run at 25W, so 2 of them would be less than your TV.

The car is 15 years old, and has the old 50W halogen ones. And actually, when you include the rear lights, it's more than 100W.

[DoctorStrangelove]

Still haven't unboxed that 4 stroke generator thingie.

The two stroke generator thingie's box disintegrated due to mice/rats/damp.

Wanna buy a generator? One neglectful owner, never raced nor rallied. .

Neither of which would run your water pump but there you go.

[DealorNoDeal]

The two stroke generator thingie's box disintegrated due to mice/rats/damp.

That's why I don't want to get a generator. We live less than a mile from the sea, and anything left in our damp old garage just rots. I'd have no confidence that I'd be able to rely on a generator when I needed it.

At least with an inverter, it's small and I can keep it indoors.