Install 12 volts In Your Home

Installing 12 volts in your home is not difficult to do for the average person and the only real issues relate to the complexity of the system and what you intend running from the 12V system and the power you require; the more complex the system the more difficult it becomes.

First comes the home survey and what you want where as this becomes crucial and the first question is where do you locate your battery/batteries as you don’t really want them in your home and ideally you need them close to your house and in a place with mains power for your battery charger.

What size of battery do you require as this is a crucial question as to get the optimum from your battery/batteries you need to be drawing less than 5% of the battery rating to get the optimum life from your battery as often to get a certain level of power it is often cheaper to get two or more batteries and connect them together. Most batteries are rated on something called the 20 hour cycle and in theory your theoretical battery rating of 100 amp/hour should provide 100 amps for one hour but it won’t as it will be dead within 5 minutes; however if you know it is rated on the 20 hour cycle and you divide its rated capacity by 20 you will get the full 100 amps from the battery. If we do the maths and divide the 100 amp battery capacity by the 20 hour cycle this gives us 100 ÷ 20 = 5 which is the magical 5 amps current we should not exceed to get 20 hours of battery life, if we stay under 5 amps draw we will get a guaranteed 20 hours of battery life.

What do we intend running from our battery system? At the very basic level it will be lighting and we need to know which rooms we will light as during any power outage any light suggesting normality is good for residents and an excellent deterrent for thieves as a lit home in a power outage means someone is home and thieves go elsewhere. I would suggest as a minimum that you light the main room with an alternative source of heat such as a wood burner as your main living room as you will have light and heat which is important during colder months and a necessity during winter. Kitchens need light so you can cook or make drinks if you have gas cookers or a camping stove as you need to see your utensils and what you are cooking as well as washing up if you boil water manually. If you have a log burner you may need an outside light to light your rear yard to your wood storage area or you may just like a 12 volt security light to illuminate any obscure areas of your property, or enough light to get to your battery store. If you have a passage you will need this illuminating along with any stairs and landing and your landing light should be bright enough to illuminate areas such as toilets for those needing illumination and enough to illuminate any bedrooms sufficiently for anyone to get undressed and dressed and a correctly designed light should do this.

We now have basic lighting covered, we have one light in the main living area, one light in the passage, one light in the passage near the front door/bottom of the stairs, one light in the kitchen, one light at the top of the stairs on the landing and a 12V outside light with sensor for security purposes. In addition to this I suggest a light in your battery store to ensure you see your batteries and if you require it you can add more lights to vulnerable areas. We now have a system containing 5 lights and an outside 12 volt security light so we can begin calculating, if the kitchen is larger it may require 2 lights so we will make this 6 lights and an outside security light, so let’s calculate.
Any visitor to Amazon of Fleabay will see the 5 metre lengths of LED lighting strip available and one decent strip regularly advertised is from a company called Lepro who produce this lighting strip and I suggest buying it with a rating of 6000K as this is nearer sunlight and better for your eyes; and if we read its specifications it draws 1.7 amps at 12 volts for a 5 metre length.
This equates to 1700 milliamps per 5 metres or 340 milliamps per metre and we can calculate this out to 170 milliamps per half metre or 500mm length and if we design our own lights we can limit the length of the strip to 500 millimetres per light and make a double sided light for the kitchen for more illumination.

If we use the basic calculation of volts X amps = watts we see that 1.7 X 12 = 20.4 watts total for our light strip as most things electrical use three measurements, volts, amperes, and watts; and like the old football pools you get any 2 from 3 and with any 2 ratings you can calculate the third rating.

Our lighting circuit now requires 2 amps to power the internal homemade lights plus whatever the outside 12v security light consumes; as these generally consume 2 amps we shall use this figure of 4 amps to calculate our wiring and for 12 volts we turn to the automotive market as this caters well for vehicle wiring and aftermarket components for the leisure sector such as 12 volt kettles, toasters, grills, etc; and they all consume electrical power. Many people may like the benefit of a cigarette lighter socket as many things plug into them and the obvious are the USB chargers for your mobile phone and most are USB type C so you need a cigarette lighter socket; in addition you may require the facility to plug your laptop or I pad in to charge it and many USB chargers are rated at 3 amps while many car laptop chargers are rated from 5 to 10 amps and this needs factoring into your design.

If we add a cigarette lighter to our wiring for charging a laptop and a mobile phone then you cannot charge two at the same time with a single charger and our laptop charger consumes 7.5 amps we can calculate our circuit requirements to formulate our design and our lighting requires 2 amps, the outside security light requires another 2 amps and our cigarette lighter socket requires 7.5 amps for the laptop charger then our maximum load requirement is now 11.5 amps and basing it on the 20 hour cycle we multiply this 11.5 amps by 20 to give a battery capacity of 230 amps to achieve the full battery capacity usage and to guarantee 20 hours of light from our batteries in a power outage.
What batteries do we buy? Now we need to be canny as a standard leisure battery capacity is 115 amps and we need 2 of these to achieve our capacity of 230 amps; alternatively a standard car battery of 80 amps capacity are regularly advertised on the internet and 3 of these are needed and will achieve 240 amps, so what are the prices, the leisure batteries are £160 each and 2 equals £320 and the standard 80 amp car batteries are £85 each and three of these equals £255 which are £65 cheaper than the leisure batteries and they all have a 3 year warranty.

With our batteries sorted out we need to connect them to a circuit and make that circuit; to do this we need automotive cable which comes in two basic forms, the standard cable and thinwall cable which uses much thinner and lightweight insulation and thinwall cables are almost exclusively used in vehicles these days. If we look at standard cable it comes in 1mm CSA with a rating of 8.75 amps or 2mm CSA with a rating of 17.5 amps. If we look at thinwall cable it comes as 0.5mm CSA and a rating of 11 amps or a rating of 1mm CSA with a rating of 16.5 amps and our requirement is for a rating to carry 11.5 amps so it is the standard cable of 2mm CSA rated at 17.5 amps or the thinwall cable rated at 1mm CSA at 16.5 amps and either will suffice. If you just require lighting alone and it only consumes 4 amps then the smaller cable will suffice; in either event I only buy it in 100 metre rolls and only ever use red and black as red is positive and black is negative and this alone keeps it simple and consistent for everyone.

Wiring is run in the loft of a bungalow and in the cavity between the ground floor ceiling and first floor, floor meaning our cables need running from the battery pack into the house and this can be done in several ways:

If your batteries are in a shed or outbuilding close to your house and it is of solid construction you can run a cable post or other upright post solidly attached to your out building and run a plastic conduit from the post to either your bungalow loft or your house between floor cavity and ensure they are sealed to prevent water and insect ingress.

You can run a conduit underground from your out building and up the side of your property wall and either into your floor cavity or loft; in either case I would suggest supporting plastic conduit overhead from a catenary wire ensuring it is 8’ (2.5 metres) above the ground to stop you banging it; always use the correct bends and run either a cable or strong string through each section of conduit as you assemble it so you can pull your cables through it.

To make your connections I prefer to use something called mini connectors which are basically a male and female plug with pins of 2.8mm diameter which are capable of carrying 20 amps and are well above our rating and therefore our requirements, so what do these fit into? Personally I prefer the small round connector boxes with the push fit lids as these are so much easier to use in a power outage than the screw lids which require you to find a screwdriver and undo the fronts in the dark and then lose the screws in the dark. Why do I prefer these? Because my preference is to fit the female half of the plug to the house 12v wiring and the male half to the light as they only fit together one way and this is much easier to do in the dark working off a chair or ladder as most people will with only a torch to work with at best.

How do I connect things together? I begin with my last socket and roughly mount in with a piece of Blue tack and this gives its position and once I am happy with it I mount the connector box and drill the two mounting holes and fit Rawplugs and screw the box into position and mark the ceiling ready for drilling, in a bungalow this is straight drilling and in a house I use extra long drills to drill through the ceiling and the floorboards of the floor above it. This gives the exact floorboard to be lifted and if you poke a wire through the hole with a piece of masking tape on you can clearly see the hole and identify which floor board is to be lifted. This box is unscrewed before any drilling and once you have located all your boxes you can begin your wiring and I suggest the following; with your wire spools at your battery site you strip some insulation off each end of your red and black cable and you twist the conductors together and once twisted you solder them so you have effectively a 2 core cable. You attach this to the string in your conduit and gently pull it through to your first junction box and leave 12” (300mm) of slack at each end, or 12” (300mm) of slack more then you need at each end; cut your cables and leave them hanging from your first box and repeat with the cables running from your first box to your second box and repeat until all your wiring is installed with 12” (300mm) of slack at each end hanging out of the junction boxes. Cut the soldered ends off and separate your red and black wire and take both your red wires and strip about 20mm / ¾” of insulation off and twist the wires from your battery to your first junction box together and repeat with the black wires so your first junction box should have 2 red wires twisted together and 2 black wires twisted together.
Take the female section of your mini connector and select the correct terminals and crimp one onto the pair of red wires and the other onto your pair of black wires; and once crimped they can also be soldered to ensure an excellent connection, push the crimped and soldered terminals in the correct order, into your plastic moulding and your first box is complete. Repeat this with all your junction boxes and all will have 2 wires in except the last junction box which will have one red and one black wire in and all your wiring is complete so you push the slack 12” of cable back into your loft or floor cavity so just your mini connector is in the junction box. If you make your own lights and the light cannot be mounted close to your junction box then I suggest getting some Blu Tack as this comes in lengths inside waxed paper, if you cut some off you can put this inside your junction box by putting it around the outer edge of the mini connector and putting your lid on. In any power outage you simply pull the front cover off your junction box and plug your light in and once you hang or locate your light you use the Blu Tack to hold any slack cables to the ceiling or wall to prevent you walking into them and damaging them.

Mounting your battery/batteries can be done in several ways and I suggest mounting them in the air at a comfortable height to see and work on them and they need to be near a mains power socket to provide mains power for your battery charger to recharge your battery pack after use, or to periodically top up the charge. I suggest you determine the amount or quantity of batteries you use and calculate the weight and build a solid wooden shelf to stand them on and allow sufficient room for your battery charger to stand on also; possibly allow additional room for an additional battery/batteries and an inverter to power your freezer as this is a popular upgrade. I would also suggest a lid to cover the batteries as this will prevent anything dropping onto them and potentially shorting them out, but leave sufficient room for ventilation as charging/discharging batteries emit gases.

I would suggest using lead acid batteries as they are cheaper than lithium and most people will be working to budgetary constraints and for a stand by system; many cannot justify the expense of lithium batteries for a system which may never or only be used periodically. What type of battery? This is crucial as many batteries have the round, taper post terminals and Ford type batteries have the flat terminals with a hole in to accept a bolt and if you can get the Ford type batteries they are easier and cheaper to wire as you only need the round terminals soldered and crimped to your cable to connect your batteries together; with the round taper posts you need the correct battery connectors.
How do you wire your batteries? Basically any battery can be wired in series or wired in parallel and it is crucial to know the difference; you can also wire batteries in series/parallel as each type or wiring achieves different things. To wire something in series we need our imaginary 12 volt 100 A/H batteries and take battery 1 and run the + terminal to our load and take the – terminal and run it to the + terminal of battery 2 and take the – terminal of battery 2 and run it to out load and wiring in series increases the voltage but not the current or A/H rating so we now have a 24 volt battery of 100 A/H rating so we have doubled our voltage but not our current.
If we wire in parallel we take our two batteries and connect the + terminal of battery 1 to the + terminal of battery 2 and take the – terminal of battery 1 and connect it to the – terminal of battery 2 we now have a battery pack of 12 volts and 200 A/H and we have kept the same voltage but doubled the current or amp/hour capacity.
With your batteries selected and mounted roughly in position I would suggest conditioning them and this is done by individually charging them, this is why you always buy all your batteries of the same rating at the same time, so they are all equal as batteries wear at different rates and a duff battery will quickly discharge other batteries connected to it. I like the current crop of digital battery chargers as they automatically sense the battery voltage and the battery current and fully charge it and even compensate for the battery and ambient air temperature and this ensures all the batteries are fully and equally charged.
Connect your batteries in parallel and once you have connected all the positive + terminals together and all the negative – terminals together you now have your fully charged battery pack and in our example we will assume three batteries so our battery pack is now 12 volts at 300 A/H and we have other decisions to make. Do we want a switch to leave our battery pack connected and if so what type? I would suggest something called a “double pole” switch which is a switch with four terminals on the back and they switch both the positive and negative terminals on and off and suggest this as in the event of any defect at least one pole will be switched off and don’t forget the correct connectors for the switch. Do you want a light for your battery pack and again I would suggest having one is a good idea so you can see in wherever your battery pack is mounted so you can see it as it is a good idea to have some light around it so you can see any issues or potential issues. On the outgoing side of your switch you connect your wiring going into your house, but if you also connect your small battery light this will also illuminate when you turn your battery pack on and is an excellent indicator of a wiring issue if you lose house lights.

To operate you simply wait for a power outage and get your torch and go to your outhouse, shed, or wherever you store your battery pack and switch it on; you go back inside your house and plug in whatever lights you need on and unplug them when you want them switched off and it really is that simple, you periodically top up your batteries with a top up charge and you will have light when most of your neighbours have none.

Many people suffer in power outages and much of this is through stupidity and often the stupidity of children as they are used to just going into the fridge or freezer to get things and this doesn’t change in a power outage as they think they will have a can of pop and just go into the fridge and get one; a second child sees this and they also go and get one and your fridge is now switched off and getting warmer every time a child goes into it.
To get around this problem we need the fridge or freezer running and for this we need power, if the mains is off we need batteries and an inverter which are now cheap enough for most people to own and I have a large American fridge freezer so will base calculations on this as it is very efficient and consumes a maximum of 500 watts. We can calculate our battery size easily.

To power this I would go to the next standard size inverter which is 600 watts and use this for the basis of our calculations which is a simple calculation of how much power do you need and for how long in hours and you multiply the two, assuming we require 600 watts for three hours we multiply the two and get 600 X 3 = 1800; we divide this figure by 12 volts and this gives our required battery capacity to give us 600 watts of mains electricity for 3 hours.

600 watts X 3 hours ÷ 12 volts = 150 amps; so we need battery capacity of 150 amps to provide mains power of 600 watts for three hours and if we take our 80 A/h batteries used in our battery pack we can get two more when funds allow to give us 160 A/h capacity to run our freezer through an inverter.

If you have multiple appliances you intend running then the calculation is exactly the same except you add together the total wattage of the appliances you intend running and remember some appliances are very electrically heavy and some are rated in watts while others are rated in amps. To calculate watts you simply multiply the amps by volts to give watts, therefore a television running off the mains at 240 volts and at 5 amps means our television calculation would be 240 X 5 = 1200 or 1200 watts and if we add this to our fridge at 500 watts we are already up to 1700 watts and if we add a DVD player to this at 250 watts our calculation becomes 1200 + 500 + 250 =1900 watts and we calculate our battery size in exactly the same way.

To get 1900 watts for 4 hours our calculation is now 1900 X 4 ÷ 12 = 634 amps of battery power which is needed and for a 115 A/h leisure battery we would need 5 of them to give us 690 A/h or 8 of our 80A/h car batteries to give us 640 A/h of battery capacity and at this expense we would forego the television and DVD.
When it comes to inverter power you can prolong it very simply by disconnecting your inverter from your battery pack when it isn’t in use as many drop to something called “stand by” and even then they consume a lot of power and doing something called pulsing. With a fridge or freezer it will stay cool/frozen for hours if it is left unopened but if you need food it is best planned so you open it once and for as short a time as possible and you don’t leave it connected to your inverter electricity as this will reduce your battery life; instead you only plug your freezer in every 2 hours or directly after you go into it. You let it run and you will hear it, when it stops you know it is frozen and unplug it; for a fridge I would suggest plugging it in every hour and let it run until it stops and unplug it.

Once you have inverter electricity you can do something called “prioritising” and that is when you unplug something such as a fridge you plug something else in such as a mobile telephone so you charge it up or partially charge it before you unplug it to plug your fridge back in. With prioritising you set the order of things you need electricity for and only use those things which you need and many things are not needed or necessary; some things can be charged from your 12 volt circuit to save your inverter mains power.
What is necessary? Basically your freezer is so you don’t lose your food and potentially so is your fridge, maybe your mobile phone or device is and the critical thing is “crucial” and because you need a charged mobile phone doesn’t mean all your mobile phones need charging as many children will also want theirs charging so they can sit and play on them; so resist this and say NO. Having children playing or texting on their mobile phone is not critical, just something they automatically assume will be done and they expect you to do and you have to put your foot down and say NO, they have light which is more than others have in a power outage and they need to appreciate that.

How does pulsing work in time; first you need to measure the time it takes your freezer to freeze down and this is done by timing it running while it is frozen as it is merely cooling it back down, your freezer will already be cold and freezing and just need its temperature reducing to ensure everything remains frozen. I measured mine and it runs for 2 minutes so I switched it off and left it for 2 hours and switched it back on and it ran for 3 minutes and from this we can calculate that it we power it up every 2 hours it will run for 3 minutes to reduce the temperature.

If we work our batteries out for our inverter to give us 3 hours of mains power at 600 watts and we now have 180 minutes of mains electricity available and if we use 3 minutes of that electricity every 2 hours we will only consume 36 minutes of electricity every 24 hours and based upon this figure we will have 4.5 days of electricity to run our freezer. If we keep disconnecting our inverter from our batteries we can see the value of having a small light next to our battery packs. If an inverter is not being used then disconnect it as they consume a lot of electricity in stand by mode.

When it comes to battery charging you can use the older type analogue chargers and in many cases they work well and do the job and the issues come with the fact they are more inconsistent than digital battery chargers and they can often cause battery deterioration quicker and be slightly inconsistent in their battery charging abilities.

Digital battery chargers are much better and incorporate a microprocessor and this basically controls more functions and it even monitors the ambient air temperature as well as the battery temperature and this all equates to a better and more consistently charged battery/batteries and many will also undertake maintenance which is often to desulphate a battery. Many generic digital battery chargers are on the market and most current digital battery chargers come with an array of functions and the ability to charge many different chemical types along with auto voltage detection and this is a necessary function along with temperature compensation.

What type is best? Switched mode types with 12 volts and one other voltage to suit your needs is a basic requirement and the more modes it can cycle through means it is better able to detect and possibly rectify any problems it detects before they become an issue and shorten the life of your battery/batteries. Many of these digital chargers come with two charging voltages and one is 12 volts while the other may usually be 24 volts and for most people this may be fine; but also 6 volts exists and many may require 6 and 12 volts as opposed to 12/24 volts so you pick the appropriate charger.

Many battery chargers have a “range” and this is the capacity of a battery it will charge and one I have has a range of 6a/h to 140 a/h so the battery should be between 6 and 140 amp hour and in reality it will charge much more than this but it simply takes much longer, so what are our options? Simply disconnect the batteries into single batteries and charge them individually. If this is simply a top up charge such as a periodical charge to maintain the batteries then don’t bother disconnecting them. Consider the charging current and the battery range of the batteries you require charging as I have some small 12 volt batteries ranging from 5A/h to 980A/h and no battery charger has this range so I use two battery chargers and like those former comedians I call them little and large. My large one suggests a lower limit of 50A/h with no upper limit and we have to remember that if a battery charger has a capacity of 10 amps at 12 volts then at 24 volts this becomes 5 amps and at 6 volts it becomes 20 amps.

Digital chargers come in a range of budgets and I would suggest avoiding the large brand names as they tend to play too much on their name while their products are little different, if at all different from the cheaper generic battery chargers often made in the same Chinese factory to exactly the same specifications and just fitted into different casings. For standby power I would avoid the large brand names with their high price tags as you can buy several cheaper models for the same money, I would suggest buying two of these cheaper battery chargers if you have 2 battery packs and you can charge them together.

Thanks Assassin, another good write up.