Running the house on a car battery

[Matty F]

There was a power cut for a few hours last night, and there was nothing to do. I could read a book by torchlight I suppose. But since I have an inverter I thought I'd run a lead from the car to the h ouse. First problem was to get into the garage that has a motor driving the door. So, into the emergency hidden door that has a secret keyhole. I conn ected the inverter to the car battery and ran an extension lead up to the h ouse.

It's a cheap square wave 1500 watt inverter, max 3000 watts (can I believe that? No!) so I was not sure which appliances would work. I didn't try the fridge, but everything else worked. The inverter does run my 1350 watt saw OK.

So I had the flat screen TV going, and the desktop computer and modem and c ordless phone and a few CFL lights. The inverter was making a beeping noise so I turned off the computer. Maybe I should have a circuit breaker somewh ere? After a few hours when the power came back on I managed to start the car ju st fine. The big V8 seemed a bit of overkill just to watch TV. Maybe I'll b uy a petrol generator.

I was wondering whether I should permanently wire a cable from the garage t o the house. If I have a generator, that will be in the garage anyway. I do n't like running extension leads in the rain at night, and I can't close th e door on the lead.

What about earthing for the appliances? If I had a permanent cable I could use the house earth instead of no earth.

[John Rumm]

I don't know what the rules and regs are going to be in your hemisphere, but I expect the same basics should apply as here. There is nothing wrong with having standby generation and power, but there are a few things to make sure off.

Firstly you need to ensure that there is no way of back powering the grid from your supply - never mind the issues of trying to run the neighbourhood off your inverter/genset, you need to make absolutely certain that you are not going to fry some poor line man attempting to get the power back on! The normal way of doing this is with a proper break before make transfer switch that only allows the standby power to be connected when main supply is disconnected and vice versa. Something like this:

Generally you should not rely on the supplied earth during a power failure. Depending on the cause of the failure, you may also find that you loose earthing as well. It does depend on the type of earthing you have though.

You may be able to assess what you have from the pictures and descriptions here:

Generally when running from a local supply, its normal to set the house (or at least the circuits you want to maintain) so they have TT earthing:

You would then normally make a neutral to earth link on the genset, and ensure you have your own earth provision from an earth spike or similar. If your house is already TT then its easy. If its PME, then you can have your own spike normally connected as well (it just becomes another of the multiple earth connections). Probably not such a good idea though if you are TN-S.

[harryagain]

It's a cheap square wave 1500 watt inverter, max 3000 watts (can I believe that? No!) so I was not sure which appliances would work. I didn't try the fridge, but everything else worked. The inverter does run my 1350 watt saw OK.

So I had the flat screen TV going, and the desktop computer and modem and cordless phone and a few CFL lights. The inverter was making a beeping noise so I turned off the computer. Maybe I should have a circuit breaker somewhere? After a few hours when the power came back on I managed to start the car just fine. The big V8 seemed a bit of overkill just to watch TV. Maybe I'll buy a petrol generator.

I was wondering whether I should permanently wire a cable from the garage to the house. If I have a generator, that will be in the garage anyway. I don't like running extension leads in the rain at night, and I can't close the door on the lead.

What about earthing for the appliances? If I had a permanent cable I could use the house earth instead of no earth.

You can buy a system such as this these days.

[Brian Gaff]

I'm surprised you got away with a square wave invertors for tvs etc, as they don't normally like hf harmonics, it confuses ther switch mode supplies. Brian

[The Other Mike]

Not another repeat of this?

or this?

[Matty F]

Actually I meant to say the capital city, i.e. Wellington. The 1998 Auckland blackout was caused by the failure of the cables to the C BD. The Wikipedia article is wrong in many respects. The cables were specif ied to last 50 years, not 40 years as stated. They failed after 30 years af ter a long dry period when the ground shrank away from the cables and did n ot transfer the heat away as usual. As it happens my company supplied the c able jointing epoxy in 1968 for those cables. The cables never failed at a joint.

Once one cable failed, the businesses in the CBD continued to use power at a high rate. They didn't bother turning off their air conditioning, which i n Auckland is not really necessary at any time. So all the cables failed an d many businesses shifted out of the CBD and never returned. They could not string 110 and 220kV cables along city streets. They had bee n digging a tunnel for the cables for some years, and eventually that was f inished.

[eastender]

I remember back in the power cuts during the miners' srikes of the

1970s my father rigged up a generator presumably powered from a car battery that kept the gas boiler going so we had central heating and hot water, which was most useful.

E.

[tony sayer]

Home made 12 and later 24 volt inverters driven off a few car batteries charged during the day when the power was on.

Mind you the switching arrangements in the fuse box were a H&S nightmare!..

[SteveW]

We didn't bother with that, we'd only had central heating for a few years so were used to being without it and the gas fires still worked without power; so we just had a 12V lamp hung where the clock usually hung and a 12V portable TV. Charged the battery back up after each power cut and used it when required. Hot water tank held enough water for whatever we needed.

SteveW