A Household Twelve volt System car Battery – By self sufficiency guru Nev Sweeney

After a discussion (email) with Andy, I thought that the “self sufficientish-ers” may be interested in myTrish electric shock cartoon by Spencer Hill experience of developing and running a 12 volt (car battery) alternative energy system through a suburban house. What follows is not the only way to do things, and may not even be the best way to do things, but for good reasons it is they way I did it and it worked for me. If you are interested in setting up your own system, I hope that this is of assistance to you.

Just for the record, I live on a smallish suburban block in western Sydney, Australia in a late ’70s vintage brick veneer house. The suburban location has driven some of my decisions.

About 20 years ago I decided to put in a 12 volt back up/emergency electricity supply into my house. The catalyst was a series of random blackouts/brownouts which happened due to the condition of the NSW electricity system back in the early 80’s, one of which caught my wife in the shower while I was in town at a meeting. That was not going to happen again! The system has now developed to the point where in most cases it is used instead of the 240volt lighting at least.

The system started out in reverse: instead of getting a power source, storage system, then wiring, I did some initial wiring, put in some lights and switches and then got a couple of batteries. To charge the system originally I used a 240v battery charger. For clarity (I hope!) I have broken down the system into the parts and will cover the history of how each part developed and where we are at now.


All the wiring used is multicore, plastic coated, two run (ie two sets of wires) non polarized, and the thickest wire that I could afford at the time. Originally that was 3.5mm thick (including plastic coating) and obtained from Tandy, the wire I use now is from Jaycar Electrical and 5.0mm thick. The multicore is more flexible and generally thicker than the single core used for 240 volt house wiring.

The original circuits have up to half a dozen incandescent lights on them and the more lights turned on, the dimmer they get. The newer circuits have only two lights per circuit and with the thicker wire, there is little or no dimming. This is the result of line losses which can be devastating in a low voltage system, so to reduce this to a minimum keep your wire runs as short as possible and your wire as thick as possible, or rather as thick as you can afford!

To connect the wires I used to use the 3M Scotchlok connectors which are designed for use on auto wiring. They usually give a quick, solid connection but can be difficult to get, and over a long time due to build up of corrosion or whatever they can give a bit of trouble. There are plenty on the wiring in my roof, but these days I tend to use 240v terminal blocks – cheap, accessible, easy to use (although not as quick as the Scotchlok) give a good solid join and they can accept the thicker wires much more easily.

Each circuit has a wired in auto-style fuse so that any short circuits do not result in a fire.


I use the normal surface or wall mounted 240v switches. The books say that the surface mounted switches give a faster break of the connection and so result in less sparking and there fore erosion of the switch terminals. They also say that the normal wall mounted type are unsuitable for low voltage and erode quickly. While not being sure of the theory, all I can say is that I have had some wall mounted 240v switches in regular use for over 20 years and have yet to see one fail in service.


The use of lights has been a continually evolving part of the system. I started out using round, clear steel and plastic trailer lights with festoon 18 watt (double ended) bulbs. They were cheap, gave good light in a small area and were readily available. I still have one operating in our laundry, bathroom and toilet, as well as one at the side of the house over the wood pile. another lightThese days the lights have a plastic backing and don’t stand up to the continuous duty of being used as house lighting, but if you can find some of the old steel back ones they are a good start, especially for small rooms.

The festoon bulbs seem to come in at a maximum of 18 watts and, depending on the quality, you may have to go through a few before you get one that lasts. Also if you do the math they consume 1.5 amps theoretically, but my ammeter says they only consume 0.5 amps, so there you go.

light 3As previously mentioned the trailer lights are good for small rooms, but for large rooms or where enough light for reading or for detailed work like the kitchen/dining room or lounge room they do not give enough light. I even found some fittings that held two festoon bulbs in a boating shop, they looked more professional but the cover/diffuser absorbed most of the light. So much for that idea!

Originally I did a bit of experimentation with a hand held fluoro but is seemed less effective than the trailer lights so the were it for a number of years. Eventually I did get onto caravan style fluoro’s from the same boating shop and gave them a go. They worked very well with a few reservations. At AU$30 they were still reasonably priced and with two 8watt tubes they gave considerably better light, to the point where I could read in the lounge room, for less power consumption. You beauty! On the down side each tube cost $4-$5 each (two per light, remember) and under heavy use could last as little as a few weeks. Damn that gets expensive! They are very sensitive to low voltage and while the old trailer lights kept going, getting dimmer and dimmer, the fluoro’s refused to work and the tubes clackered. They also show up line losses like nothing else!

Still, up until a couple of years ago, that was the state of the system, fluoros and trailer lights. Then I discovered halogen down lights – cheap, good point lighting and the bulbs last a long time. I installed two over our bed as reading lights and they have given good service for 5 years or so. Now I have one over the stove, one over the sink and two over the dining room table (lighting this as I write). The down side is that they chew power, and as a hint, use the 20 watt bulbs not the 50 watt ones supplied otherwise you’re likely to give your batteries a heart attack!

lightThe search goes on and when the fluoro in the lounge room finally expired I consulted a specialized 12 volt remote area power shop. They turn me on (pardon the expression) to high efficiency fluoro’s, and my they are impressive. Low power consumption, the tubes are rumoured to last forever, mine has only been in for a few months but gets anything up to 12 hours use a night (kids!) and the light level is as good as any 240 volt light I’ve ever used. The downside (there always is one!) is that they cost $118 each! (bloody hell!) I’m saving up to put one in the area between the kitchen and the dining room to give better over all lighting (the point lights don’t illuminate the fridge!).

So there you have it, what started out as a backup has now become our main lighting system and the system is still evolving.

2 Comments on A Household Twelve volt System car Battery – By self sufficiency guru Nev Sweeney

  1. very interesting nev

    i got myself a mobile home and plan to get generator, deep cycle batteries to power(12v) lights, laptop, phone charger, radio.

    so you recommend at least 5mm cable and only 2 lights per circut even with the high efficiency fluoro’s?

  2. Howdy, i read your blog occasionally and i own a similar
    one and i was just wondering if you get a lot of spam comments?

    If so how do you prevent it, any plugin or anything you can
    advise? I get so much lately it’s driving me crazy so any support is very much appreciated. Kudos!

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