How to run a house off the car battery

With yet more news from Bishop Hill of another coal powered station closing down, the likelihood of power cuts grows.

So, I’ve started thinking about how to deal with power cuts in a more robust way than a few candles and torches.


Note in the UK the electricians lied to parliament about the dangers of mains wiring (including the much larger number of fires from portable appliance in order to suggest that wiring was an issue when it is not). So there’s some kind of unenforceable rule that only members of the union can do union jobs — unless it’s your own house — when they still try to enforce the non-scab labour rules.

The reality is that if you have an RCD protected fuse box and are reasonably careful you are as safe as you can be from all but the petty bureaucrats.

The problem areas

  1. Lights are the first indication most people have of a power cut (they usually occur on winter nights). And power-cut dark is not just dark as we normally experience it (with external street lights) but pitch dark. Not a huge load – but permanently wired so difficult to power without permanent wiring.
  2. Fridge-freezer. Not the biggest load in the house (We have had 240-516W if I remember right), but still big relative to most appliances and worse an inductive load needing a fairly beefy supply and can ruin cheap inverters.
  3. Central heating. If you live in Scotland – you’ll already know that you need mains to run central heating. So you know that both heating and hot water (instantaneous) goes – even if you have gas central heating. Difficult because it is usually permanently wired and it’s an inductive load which can kill some cheap inverters.
  4. Phone, internet, comms equip. We’ve all grown so used to instantaneous communication, that we e.g. do not use a phone directory but instead search the internet. We have mains powered landlines. Even mobiles need charging. Individually they are not a problem – but when they all go down together it is a nightmare.
  5. Kettle – at 3.5kw kettles are amongst the biggest loads in the house. Even travelling kettles are 1100W and it is far cheaper to buy a camping gas stove and kettle than massively up the spec of your generator to suit this one appliance.
  6. Dishwasher & Washing machine – both contain kettle sized heating elements and inductive motors. Those living off-grid tend to buy their washing machines to suit their generators and wash by hand. So unless the power is off for weeks – just let the washing pile up.
  7. Electric showers – need insane amounts of power.

Car battery mains inverter

For as little as £30, you can buy a plug in adapter for the car with around 60Watts output. Realistically this will just about power a big laptop OR a small TV OR a few LED lights. It won’t power a fridge (or central heating). Unless you have a garage and start living in it you will also need several extension leads.


  • Mains adapter for car. 60W gives around 8hrs, a 240W main drain battery in under 2hours
  • Long extension lead from car to house
  • More long extension leads to get power to other rooms
  • A plug in LED light for each room

Separate mains generator

Generator (diesel/petrol/gas)

There are relatively cheap diesel or petrol mains generators, but if these are anything like the cheap chain saw I bought, they never work when you need them and they are noisy.

But fuel is easy to store (but outside not in a house) and more is easy to come by and (if you can find a petrol station with a pump not affected by the power cut) fuel is available to run almost indefinitely.

Being an inductive generator, they will happily power inductive loads like fridges. So the main concern is whether it has the rated output.

Battery + inverter (NO inductive/motor loads)

(remember lead-acid batteries can generate hydrogen gas – so they must be vented to outside)

Likewise, I’ve had separate lead acid batteries and generators. The problem is that they will run out eventually and surprisingly quickly if you use more than just lights. The biggest problem is their initial cost, finding somewhere to keep them and ensuring they are topped up with charge for the years between power cuts is a problem.

To power non-motor loads like some lights & TV (not kettle) you’ll need a good camping battery and a big inverter. I have a 240W inverter that powers a lot of odd equipment, but check the equipment and make sure your peak load is well within the peak output. The bigger – the less likely to trip it – but the faster it will go through the batteries. And check efficiency, because a big inefficient inverter may quickly drain a battery even without any load.

Battery + inverter (WITH inductive/motor loads)

Inductive loads such as fridges, central heating pumps, and motors (anything with big/fast moving parts) and inverters don’t like each other.  Not only do they have a massive inrush current that means they use perhaps 3x their average load at start, but they try to push all that power back into the inverter which if it’s not designed to cope will go up in smoke. So, an inverter has to be purchased to suit the loads – and it will not be cheap – perhaps £200+.


  • Diesel/Petrol Generator
  • Fuel
  • Big Battery (12v 100AH)
  • Inverter specked for equipment (at least 600W)
  • Charger (ideally one that can be left charging permanently)
  • A long Power lead to reach each room + multi-way distribution leads to any equipment in each room
  • Plug in lamps for each room

The ideal solution would be a large lorry battery (24V) with more than 100AH capacity which would give 6 hours standby at average household consumption of 400W. But the inverter needs to be capable of driving large inductive loads like a fridge.

Separate Mains Generator + plug in circuits

So far, all the equipment has been powered directly by plugging each piece of equipment into the extension leads from the portable generator. However the next step is to create plug in circuits power permanently wired from the mains.

“Plug in” Central Heating

Typically a boiler is on its own circuit and its not that uncommon for them to be plugged in rather than hard-wired in. So, all we need do is convert them back.

A boiler doesn’t use a lot of electricity when running (200W?) but its a dog to start. (see above).  Typical fuse ratings are 3A which suggests a 750W. A petrol generator with that rating should be fine, but not an inverter. An online forum recommends 1kw and probably a “true sine wave” type.

However, if there is a generator/inverter available with the right power, it can power the central heating meaning you will have heating when others are shivering. This requires a relatively simple change. Usually, the boiler runs from its own power spur and if like ours the final connection is a appliance cable from a wall outlet, this wall outlet merely needs converting to a socket and a plug added to the end of the appliance cable.

Then if there is a power cut, you simply unplug the boiler from the dead mains, and plug it into the live generator.

“Plug in” circuits

The way to do this is disconnect the circuit from the main distribution unit and then to wire it to take power from a plug. Then the circuit from the mains distribution unit is changed to be a power socket circuit with a single plug. Finally, the plug is goes into the socket and power is restored. So, now the circuit – let’s say downstairs lights – works as normal. It is fully protected and quite safely plugged into the mains.

Then if a power cut occurs, that circuit is unplugged and plugged into the separate generator.

Lighting circuits

A normal 13A (UK) plug will work fine for 5amp circuits (like lights). However if you are going to effectively convert the circuit to a spur, you need to upgrade the wire as far as the socket (if the circuit is converted back the socket it may end up being used as a socket so the wiring should be rated for that). The plug will have a fuse – which is now the main protection for the attached appliances. That suggests the fuse should be as small as the lights attached will permit (2 or 3Amp for a lighting circuit), however, that now means that if there is excess current which sometimes happens when filament lights go – instead of the mains fuse going where one normally expects the fuse, the fuse will go in the plug. This is a problem mainly because many people will not think to look at this plug fuse.

Remember all this fault finding could be done in the dark!

  • One approach is the increase the size of the plug fuse so that the first fuse to blow is in the distribution box.
  • Another thing that may help is a neon power indicator in the socket
  • Another approach is so that not all lights are plugged into the one plug. This way only some of the lights will go out. Turning off the circuit – will turn off lights which were on showing it is working. That will quickly indicate that it is a part of the circuit that has blown – thus pointing people toward the plug (which if there’s a neon will turn off and on showing it is part of the lighting circuit).
  • Another possibility is to use the 5Amp round plugs which are unfused. These were often used for almost the same type of application whereby they powered standing lights around a room which were switched on and off from a central light switch.

I can’t say whether it breaks any codes – my feeling is that it’s more likely to be objected to by people like building standards who might insist it is not permanent light rather than electricians. The round pin plugs are often used to plug in permanent lights – so there shouldn’t be a problem – but common sense doesn’t always prevail (and in Scotland the council behaves as if it owns people’s properties and so they go way beyond what is reasonable).

From an electrical point of view it should be safe (but see grounding below) – and what building standards don’t know about doesn’t concern them. A bigger problem may be trying to sell a house with such “non-standard” wiring. So, a plan to be able to relatively easily bypass the plug-socket to make it into a standard domestic circuit again would be sensible.

Power circuits

As I said, a 13Amp socket will do for many circuits, but not power. But if you want to power something like a fridge you need a power circuit. A single spur would probably be rated 15-20Amp which is too much for a 13A plug. But caravan sockets are rated at 16Amp and intended for just this type of permanent wired application.

However there will be problems with a normal domestic ring main which is rated 30-35Amp. I don’t know of a suitable plug with this rating. There may be something available but with bigger loads it is not sensible to try to connect in a ring main. So, the best strategy would be to select a few essential sockets and run these as separate spurs. These should be well marked because because anyone working on these sockets will expect them to turn off when others in the same room turn off.


Rewiring the new “distribution box”

It is likely that you have several mains cables going into the fuse board. These need to be rerouted to a new place where they can be brought together and then this needs connected into the mains with a plug lead and plug. Then you need a socket which in turn is connected to the mains.

It should be quite safe, but I have no doubt that some “professional” electricians won’t have a clue about anything unusual and may insist that it’s got to be a permanent wired ciruit for them personally to pass the circuit. So, I would put it together so the plug is relatively easily replaced.

You want people to consider these plugs as part of the mains circuit and not a handy point to plug in a vacuum. So, if possible try to find non-standard plugs that look “electrical” and then have an adapter to a 13A socket to plug into the generator. At the very least – there are orange sockets available and some handy “lightning” symbols will make it all look official. And if possible try to put all these power sockets in a purpose made box so no one is even tempted to use the plugs for other purposes.


The generator equipment is as above but will be larger. A bigger system will need bigger equipment and bigger more expensive batteries (if you use an inverter). So you will want a purpose made charger for standby use that keeps the battery properly charged and can remain connected during a power cut.

Simpler setup

Off_Grid_singleAbove is a possible schematic perhaps a lighting circuit. A single wire comes out of the mains distribution unit to a plug (5Amp, 13Amp or caravan would do). The fuse should be rated according to the plug – but if not  the plug needs to be distinctive with warning signs that it is not fully rated. Try to arrange so that if at any point someone wants to remove the off-grid connection, the plug can be removed + the wire to the mains can just be rerouted to the distribution box

More complex

The above could be used for several circuits, but I expect any electrician will take a very dim view if e.g. the upstairs lights can be connected into the socket going to the downstairs lights (and quite dangerous if anyone works on the lights). So, for a more complex system, I would consider something like the following. Here we have added in another consumer unit (as available for caravans). Now we have a single power lead and in essence we can treat it like a caravan – except …



Not quite worked out grounding. In principle grounding works by ensuring all bare metal which is not electrically isolated in some way  – is all at the same potential. It doesn’t actually matter if its all at 230V – so long as you can’t then touch something at 0V (relative to the earth outside)

If no RCDs are used in the circuit, then that means to ground everything you can. So, that suggests a permanent connection to ground. If the added fuse has RCD protection, then most should work, but to be safe I suggest grounding the plug side of the fuse box with a great big ground connection (enough to take all the current but something that looks robust will convince most elections so perhaps 10mm2).

Going the whole Hog

The ultimate solution approach is to have a very simple switch that disconnects the whole house from the mains supply and then connects it to an inlet socket.

The big problem is that the switch will go before the consumer on/off switch so you will have to bring in the electric supply company and convince them to install the switch.

But once you have the switch, the great think about this approach, is that the wiring is now all non-mains so you can stick two fingers up to all the electrical union cartel imposed domestic wiring rules as all that now matters is what is safe and sensible. (Although seriously, your house probably comes under rules usually intended for things like caravans and without the same strong arm tactics of the electricians unions these are probably what is sensible rather than what makes works for electricians)

So, one way to use this approach is to have a caravan style power inlet socket. The generator is then connected from outside to the socket and in theory by turning the switch, the WHOLE HOUSE can be off-grid.

But realistically a 16 amp lead cannot power everything in the house, so you would need to go around disconnecting all the big power users like washing machines, kettles, etc.

The problem with this approach is that because we are so used to just turning things on (like kettles) it may prove to be very unreliable as every time there’s a power cut, someone forget that there’s a power cut, turns on the kettle and trips the power.

The other problem is that you’ve no way to know whether your power is back on. In reality, you probably need an additional distribution board powering a few lights.

How to run a house of a car battery

And if you do go the whole hog and if you disconnect all the circuits leaving only the lights. (or remove everything from a power circuit) And if you turn off big fluorescents and leave a few very small LED lights turned on.

Then you can literally run the house from a small inverter fitting into the car.

But if you are insane & lazy & generally have a death wish & you live on your own
and basically don’t!!!


!!!!!There is an option of creating a lead with two power plugs.!!!
!!!One end plugs into the inverter plugged into the car!!!
!!! the other plugs into a mains socket.!!
!!Note this is a hypothetical lead and to make one like this is insane!!!

Don’t – but if you do – a short lead in very distinctive colours and lots of warning signs is less likely to be mistaken for an extension (and it gives the emergency services coming to retrieve your body a better chance).




(There should be a switch so it should read “switch off here then disconnect” BOTH ENDs FROM MAINS”


In theory, you unplug and turn off everything in the house leaving just a few lights and perhaps a few low-power devices plugged in and the house is powered from the car cigarette lighter.


BUT I REALLY DON’T KNOW HOW ANY RCDs will react – but anyone who tries this probably doesn’t have any RCDs.

But in theory just as CO2 should cause global warming (note there’s been no warming for 18years), so should you be able to power the house from a car.


On a serious note

Obviously it would be stupid to plug in a house to the car because:-

  1. Modern cars have so much sensitive electrics that would be fried if mains got anywhere near it and there’s a serious risk mains go back through the inverter.
  2. You have live wires if you disconnect the wrong end of the lead (and the wrong end changes depending which way the power goes)
  3. You have a really unsafe lead which could easily be mistaken for an extension and you would have to treat it like a loaded gun.
  4. You bypass all safety equipment, probably break multiple rules and

However, whilst a hard-wired lead is unsafe, it might be possible to design a lead which disconnects if no current is flowing. So it would immediately disconnect when unplugged (there would need to be a small load at both ends to keep it connected). That’s not too difficult a task.

What I’ve not yet worked out is how to disconnect the lead if someone accidentally turns on the mains with the lead connected.

If mains goes back down the lead it is possible it could destroy the inverter and anything else connected to the battery (i.e. the car) and possibly leave exposed mains on battery terminals (if the battery does not explode with acid flying everywhere!). However, inverters/generators are designed for mains and they should be tested to fail safe if at peak voltage the output is shorted to ground. That’s only half the voltage of a short, but it is just possible a generator or inverter might survive albeit suffering a massive power surge – but it might just survive long enough for a quick trip fuse to blow.

Paradoxically the worst scenario is not catastrophic failure which likely ends with a loud pop which will make it clear the equipment is dangerous but if the generator is in phase with the mains and then locks into the mains and keeps running.

A SAFER APPROACH rather than double ended lead

If you are intent on plugging the house into an inverter it is madness to have a doubled ended lead, a better approach (but still not safe) is to create a purpose made device as follows:

Affix a board to the bottom of a solid non-metallic box with a lid. Connect two sockets to this board and wire in plugs to each socket. So far this is fairly conventional – plugging in either or both plugs will power up the sockets in the bug.

To make it safer than an open double ended lead  (but not safe) one approach (if you insist on going ahead) is for the box to have TWO switches that disconnects the mains from BOTH sockets when it is opened. NOTE DO NOT USE protruding switches which can be accidentally turned on.

The box should have an appropriately rated quick blow fuse and I also I suggest adding a machine type switch outside the box which is push to make so that the power can only be turned on when the lid is closed.

Now create a short power lead, which is not long enough to come out of the box and most importantly, take the lead through part of the base so that it is impossible to remove from the box without cutting in two.

Now you can open the box and there is no power or anything live to touch. Then if one were mad enough to try, one could connect in both ends of the doubled plugged lead and shut the box.

I’ve just realised  that after all the building of this box, I’ve just pushed the problem down the line because now the two plugs on the leads coming out the box can be live. The only strategy that avoids live terminals is to hardwire it in some how – which then needs an inverter where the mains lead is permanently attached. I suppose one could glue the plug into the inverter … or perhaps put the inverter in the box and run low voltage leads to car (but they’d need to be massive cables because with large currents and low voltage the slightest resistance eats away at power)

But what I cannot protect against is the human stupidity because the first thing we’d want to do after a power cut is to turn on the mains – and ironically – the safer the connection appears to be the less likely we are to remember about it before we cause an almighty big  !!!BANG!!!

The closest to even barely acceptable is some kind of massive (100A mains) changeover switch that makes it impossible for the house to get power from both the generator and mains at the same time.


Another strategy is to put the plugs on the ceiling. That way if electrocuted, you might fall and break your neck, but you will be disconnected from the mains.

And … we have just the points to do this in most homes AKA as light bulk sockets. There used to be adapters for these. If one had one of these a push to make switch which only stays on when there’s a load would stop mains appearing at the end except when the button is pressed or it’s in the socket.

Had a look and the easily available machine switches (i.e. cheap) don’t have a current sensing capability. However there are current sensing relays at around £50 which could be made to break the voltage unless there is a current flowing – and to start one then just needs to have a push to make switch to bypass this. It’s also worth having a fuse.



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12 Responses to How to run a house off the car battery

  1. TinyCO2 says:

    First off, there’s a thing called a power pack which is essentially a car battery that plugs into the wall to charge and has a standard 3 pin socket on it anyway. They vary in price and other gadgets, eg jump leads for your car, type pump etc.

    For lighting, just make do with torches. You don’t want to be living a normal life with a power cut. Another alternative is christmas LEDs. They’re low energy but bright enough to do stuff. I’ve even got wind up torches that are useful when you run out of batteries.

    What you do about heating is up to you. You could leave the three pin plug option until blackouts become regular. It might be worth investing in electric blankets. I’ve got a few electric duvets but I don’t think they do them any more. They use loads less energy that fan heaters and I’ve used them in a room where the water in a glass froze, and didn’t feel the cold. It was a bugger getting out of bed though.

    There are plenty of options to heat food but people need to remember not to use exterior equipment indoors. People die most winters trying to use BBQs for heat. Generators are another source of deadly carbon monoxide.

    However, power cuts are not likely to become regular. It will damage business first and you’d be surprised how fast new stations go up once that happens more than once. Business uses a lot of energy and if we were on the brink they would be shut down. Another option is rolling blackouts where you get time each day to keep your freezer cold and allow you to do some essentials. People would also be asked to minimise what they do – eg no vacuuming. What we might see is a week or two of disruption and then a rapid build.

    • Scottish-Sceptic says:

      A portable supply would be great – it just seems there ought to be a neat way to power the house from it.

      In theory all it takes to power a house is a doubled ended lead – whose components can be bought from ebay for a couple of pounds and plugged into the mains and a cheap inverter. I could literally have that done in 15minutes.

      Last time we had a power cut we got our camping light working fine – but finding somewhere to hang it was a nightmare – particularly when all the places where I had bits to make hooks were in dark.

      But with LED lights and my 240W inverter I easily have enough power to have all the lights working – I just need to get organised.

      Perhaps I just like the thought of it … can you imagine what the neighbours will think!! It will be completely dark on the street, a few very dim lights just showing indoors.


      All that’s stopping me is bridging that short distance between the mains wiring and some portable supply.

      • TinyCO2 says:

        My Dad worked in the Power industry during the power cuts of the 70s. He had small lights he hooked up to a car battery and one of the neighbours thought we had power because of his industry connections and was all set to have a punch up.

        A car battery wouldn’t last very long with anything other than small items. Save it for a laptop and low energy lighting. If you want anything like real power then it would have to be a generator. I’d suggest you get an electrician for anything significant. Remember you have to make sure you’re not connected to the grid at the same time you power yourself. Extentions leads off a Powerpack or generator is more sensible unless a real crisis develops.

        I was heavily into pandemic planning at one point and we looked at what a failed grid might affect. I read loads of documents, had meetings with utilities etc and I’m fairly sure that even with a depleted fleet there wouldn’t be long blackouts. If you’re halfway healthy and not running a business, you’d be fine. The elderly however would suffer a lot more. A lot of essential stuff needs power, from stair lifts to emergency buttons. Care homes were advised to get generators but I doubt many complied. Business would also suffer and any government seen to have twiddled their thumbs while the fleet shrank would be savaged.

        If there was a major series of powercuts, then keeping your household running normally would be the last thing on your mind. Lots of other stuff stops working – eg shops, mobile phones, cash machines, even the other utilities if the battery backups run out or fail. Things like petrol become rationed or even reserved for certain professions. My theory that such an event would be triggered by more that just a shortage of power stations. It might be a serious pandemic (of which there are at least 4 major contenders), a massive fuel strike, a series of well placed terrorist attacks or even a strike in the power industry itself. At that point your priorities would be non perishable food and clean water. Most people who were involved in pandemic planning have a personal plan, part of which is to keep an eye on what’s going on in the world.

        eg one of things I did was test tinned food so that if I had to buy in a hurry I didn’t end up with stuff I hated. I made lists of things in order of importance so I didn’t have to start from scratch in a panic and/or I could pass the list on to others.

        • Scottish-Sceptic says:

          Starting at the end – at one time I filled a box with various tinned and dried food – but I soon needed the space and in any case they all have use by dates.

          What is probably needed is to buy a box of food – put it somewhere where the mice can’t get at it – then at the end of the year, buy another box of the same food and put the first lot in the store cupboard. But with teenage children who already laugh when I highlight all the older tins at Xmas to ensure we use older ones – i know just what they would say if I brought out another box full of “hard ration” tins which last for years.

          On the battery – yes it’s great, but the biggest problem is that we currently have too FEW power cuts to be properly prepared.

          When I had a lot of working test equipment I had lead acid batteries and would use those with 12V low-voltage lights. But now I’ve stopped using those big batteries they’ve had to be junked and now I really struggle to get decent lighting.

          That’s the biggest problem – making sure you’ve got a well charged battery and the only battery I know I currently have which I can rely on is the one in the car which is checked & charged each time we use it.

          Since power cuts are going to become regular – I should probably get a big battery going on standby charge so that it is always available.

  2. fjpickett says:


    Which people will flock to if they think you’ve still got power.. :-)

  3. TinyCO2 says:

    A good reason not to fiddle with your electrics, is your insurance.

    • Scottish-Sceptic says:

      Someone did an analysis of fires supposedly caused by house wiring in the US. There finally summary was along the lines of “almost none of the dozen or so cases where faulty wiring turned out to be a possible cause could actually be certainly attributed to wiring”.

      In contrast, I think there’s something like 8000 fires caused by equipment.

      And officially I’m qualified having done the “course” when I worked in a factory – and I’ve even got all the test equipment having wired our own house (it being far cheaper to buy equipment in a one-off payment than to pay someone).

  4. Oswald Thake says:

    If, or rather,when, we have power cuts, the Government will see to it that our large cities have power, if only the prevent the more diverse and vibrant of the population rioting and going in for some painless free shopping. But then, if I were in charge, I’d see that the rural Nimbies on our shale gas deposits would be the first to lose power, and the last to have it restored.

    • Scottish-Sceptic says:

      The only thing we can be sure of – is that the least likely places to have power cuts are those with politicians in them.

  5. stewgreen says:

    Congratulations Mike, President Obama says you are the new Elon Musk and your solution is 10 times cheaper than Musk’s hyped up magic battery packs he’s going to award you a $900bn subsidy instead.

    Two lorry batteries and an inverter that’ll do the trick.
    I wonder if you run an extention outside to your cars running engine many KW it will give out ?

    • I once had a 70W turbine for testing equipment about a meter across. On average, it would give around 10-20W of power – and it was noisy as hell apart from charging the odd battery it did nothing.

      However, you’d be amazed how many people thought I was running my house from it – people just don’t have a clue – in reality it would need to be about 3m across and I doubt many would have liked to have come near the house if I had one.

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