There are so many new 12Volt appliances and devices that are regularly added to our range of choices that it’s hard to keep up sometimes. This list will therefore remain a moving feast, and I’ll update it as new 12Volt stuff becomes available.
The current draw (in Amps) of 12Volt devices will typically be either on the equipment label itself or somewhere in the specifications part of the manual. Sometimes the power draw (in Watts) will be shown instead, and in that case just divide the Watts by 12 Volts, and that’ll give you the current in Amps.
So why do we care how much our 12Volt equipment uses?
I’ve put this bit upfront, as it’s the single most important figure we can use for working out the size of a 12Volt system. It’s also the starting point for the articles on How much Solar? and How much Battery?
It’s the solar’s job to put back what I’ve taken out of my batteries, and it’s the battery’s job to store the solar energy so I can use it any time, day or night. So to be able to work out how much solar and battery capacity I’ll need, I first have to work out how much energy I will use. Let’s look at a simple example.
For 12Volt camping and caravan systems I prefer to work in Amps and Amp-hours, and to then work out what a typical day’s usage looks like. We will also use this later to calculate our battery and solar sizes. So let’s say we have a simple case of:
Using the table below, we can see that the fridge will be the main culprit, at about 35Ah/day for average use. However for our solar input we are going to use the worst-case of winter-hours, and to match that we are going to use 25Ah/day for the fridge. That way both the solar and the fridge have figures which reflects winter conditions. (see heading below on Fridges).
Then if we use the TV for 5 hours, this will add another (5hrs x 3Amps) = 15Ah/day. And if our LED strip-lights are used for 5 hours a day, then that’s (5hrs x 1Amp) = 5Ah/day.
This daily figure can be tailored to suit our individual needs by modifying the figures to suit, and by adding other 12Volt devices to the total. For instance if I only use my TV for 2 hours instead of 5 hours as in the table, then the TV’s contribution will now be (2hrs x 3Amps) = 6Ah a day. In this case I will be saving myself 9Ah every day, compared to the 15Ah in the table.
The following headings are in alphabetical order, and each device and its typical current draw is discussed, and then summarised in a table at the end. There are always variations to these “typical” figures, so the discussion is to help us tailor them to our particular situation – and for fridges the discussion gets a bit longer as their energy usage tends to vary quite a bit. From the table it’s also easy to see why we pay special attention to 12Volt compressor fridges – they use the most power.
Most of the newer models will either work directly off 12Volt or they have a 12Volt adaptor that will plug into a cigarette socket. They will work fine off an inverter but the downside with that is that the power losses, which means we may not get a full 8 hours out of our 12Volt battery, so it’s best to avoid an inverter if possible. It’s not easy to get actual power consumption data on these machines – mostly you’ll get maximum power or current being specified. One thing that is consistent throughout the various makes and models is that turning the humidifier off reduces the current draw to a half or even less. After some considerable trawling through the various makes and models it appears the best guesstimate for CPAP machines is a daily draw of 15 to 30 Amp-hours. This assumes an expected use of 8 hours a day and that the humidifier is off.
Update: It seems there are also some very efficient ones out there – just 6Ah for a good night’s sleep! Take a look at the info in Hilto’s comment below – might be worth doing some research…
Now this is one way to keep things warm efficiently, and because 12Volt systems are limited in the power they can provide, this is a great option. So you’d think that most retailers and online shops would carry them, right? – yeah, so would I, but turns out we’d be wrong. Apart from the eBay stores which can be a bit of a Russian-roulette at times, I can only find one Australian-based store that sells 12Volt electric blankets, and they’re a bit pricey too. But when it comes to something I’m sleeping with (so to speak) I want to be as safe as possible, so I’d rather pay for that peace-of-mind. Typical current draws vary from about 3 to 6 Amps, so using the 3Amp model as a pre-warm blanket for 2 hours a night will use just 6Ah (2hrs x 3A = 6Ah). Leaving it on a lower setting during the night is also possible with some models.
Running a 240V electric blanket through an inverter is an option, but not a good one. Firstly I’m not that keen on having my bed wired to 240V – at home I switch off the electric blanket before I get into bed. And secondly, introducing an inverter just increases our losses – the very thing we were trying to avoid!
So for myself I’d rather stick with the more efficient and safer 12Volt versions, but now that you know the ifs and buts, over to you.
12Volt fans that have been designed in the last 5 years or so will be using the very efficient and quiet brushless DC motors. These fans move a good amount of air and are the only practical alternative to a 240Volt air-conditioner. They come at a bit of a price but there are well-established brands out there, and they are stocked by most good retailers. Their current draw is below half an Amp at 12Volts so even leaving it on for 8 hours will only take 4Ah from our battery (8hrs x 0.5A = 4Ah). The better ones also have a timer which can be set to turn the fan off automatically after a certain time.
Here we are talking 12Volt compressor fridges, and this is one of the most tricky items to pin down in terms of power draw. But because it’s also the biggest power draw in most 12Volt systems it’s really important that we get this one right. (The article on Fridges has more info on non-compressor fridges that run on gas and the little cooler/warmers).
Manufacturers of fridges tend to use test conditions that will show their products in the best possible light. So tests with fridge temperatures of 5°C and ambient temperatures under 30°C are quite common. These are however very seldom the temperatures us average campers come across – unless you like warm beer and travel only in mid-spring and mid-autumn. The tests also don’t specify how often the fridge is opened and closed – maybe they just keep it closed while testing to minimise current draw – who knows?
Anyway, the figures in the table here are based on actual tests I did of typical 12Volt camping fridges available in Australia. We used both the Engel range and Waeco-CFX range of fridges side-by-side. They were tested over a number of months, including summer conditions with ambient temperatures above 35°C, and the interior temperature setting was -5°C. We ran two types of tests – fridges left closed, and fridges loaded every 24 hours with up to 12 litres of room-temperature water – this gave us a whole range of power consumption figures which mimic the way in which us campers typically use fridges in real life.
Of course the figures aren’t perfect – no test ever is, and everyone’s situation will differ – but it does give us a set of real-world figures to work from. And by-the-way, in terms of power consumption there was very little difference between the two brands – some won some days, others won other times, but on average they were surprisingly consistent.
When we loaded the fridges up with a full 12-litres of room-temperature water, as you’d expect the consumption went up. Also, over long weekends the fridges would be left to themselves, and by the second day the energy usage came way down. These are the Low and High figures in the table. So if you’re freezing your summer catch each day, then expect the higher figure. If you’re camping in the cooler months and just want the milk & veges to stay fresh, the lower figure will be more likely.
There are a number of brands out there, and except for the Engel, they tend to use the Secop (Danfoss) compressor, so from that angle their usage will all be quite similar. The other big factor that affects fridge efficiency is the insulation. Better insulation means we lose less to the outside atmosphere, so we use less energy. For instance if you compare a household 240V fridge to a 12Volt camping fridge, the difference in insulation thickness is pretty easy to see. The same is true if you compare Waeco’s CF and CFX range – the CFX has much thicker insulation, and the CF-range therefore uses a good one-third more energy than the figures in the table. Also, National Luna fridges inject their insulation at high pressure so it’s very dense, so it takes up less room and is very efficient at keeping the inside cool.
Upright compressor fridges are typically 80 litres and up, all the way to 220 litres and the bigger ones usually have a separate freezer door. Engel also make an 80 litre freezer-only with a slightly bigger compressor, which can be paired side-by-side with their 80 litre fridge-only option.
Uprights obviously use more energy than the same size chest-type, especially if the door is opened often, but uprights are much more convenient in caravans and can be built-in. In terms of energy usage most uprights use the big BD-50 12Volt compressor, so their consumption then depends on the amount of fridge-gas used, which increases with fridge size. For a 110 litre upright we can expect to use about 90Ah a day at 12Volt, and for the bigger sizes this can go to 125Ah a day and upwards, especially if it’s working hard.
With all 12Volt compressor fridges, if we are using solar to replenish our batteries, then we have a bit of Mother Nature on our side too. In summer the fridge is working harder, but we also have more solar power available. Same thing in winter – we have less sun but the fridge has a pretty easy time keeping things cool, so all round we have a nicely balanced system.
The power that an inverter will use from the 12Volt system is determined by the power of the 240V equipment we have connected. In the article on Inverters we devised a quick-and-easy formula to calculate the current on the 12Volt side of things – we simply divide the power by 10, so knock off a zero. So if we have a laptop running on 240V through an inverter, and its power-supply is rated at 80 Watts, then we will be drawing about 8 Amps from the 12Volt system. So a 5 hour session on the laptop will draw 40Ah from our battery (5hrs x 8A = 40Ah) – quite a considerable amount. There is an article on Inverters which gives more detail on these hungry little beasties, and the short version is that inverter use is best kept to a minimum.
Anything that has to do with heating is always a bit of a challenge for 12Volt stuff – we don’t have much voltage so to get the power up (Watts) we have to increase the Amps (Watts = Volts x Amps). And then the issue is that above 15Amps or so we start to stretch our friendship with a few things – plugs, cables, sockets, and also our batteries.
Waeco makes a very good 12Volt kettle that stretches most of these parameters a bit, but it still works pretty well considering what it’s up against. The compromise is that it takes 3 cups (750ml) and takes about half-an-hour to boil. So if you were hoping for a quick cuppa while you park beside the road, then it’s probably worth sticking to the gas. On the other hand I find that in the morning, if I hit the on-button when I wake up, by the time I’ve washed my face and worked out which way’s up, the kettle is boiling happily for our morning cuppa. Anyway, it’s another 12Volt option that’s out there, and it draws about 15 Amps for ½ hr so its energy usage is about 7.5Ah to boil a full kettle of 3 cups.
Many years ago I was impressed by some funny-looking diodes that emitted a red glow if you passed a current through them. The moment I saw them I knew this was the future of lighting. The old incandescent bulbs produced 98% heat and just 2% useful light. This made them an easy target to beat, but they remained the best option for over a hundred years. Halogen bulbs were a lot better but were very soon superseded by LED lighting. Fluorescent tubes remain as efficient as LED, and in some applications they are still the best option when coupled to an efficient 12Volt ballast.
But LED lighting has completely transformed the interior and exterior lighting for camping and caravanning of all shapes and sizes, and is now far-and-away the most used technology for 12Volt systems. LEDs use about one-fifth of the power compared to an incandescent (glow-worm) bulb. It’s therefore tempting to disregard any power-draw from LED lighting as “one-tenth of buggerall” – but this is often not true. For instance a flexible 1.2 metre-long LED strip-light draws close to 1.5 Amps, and over an evening’s use of 5 hours or so, this one light will set our battery back by 7.5Ah (5hrs x 1.5A = 7.5Ah). Now even with a smallish 100Ah battery this is not too much, but if there are a number of other lights running at the same time, then things can start to add up, even if they are LED.
If you have light fittings with the older 12Volt Halogen bulbs in them, these can easily be replaced with LED-bulbs which usually provide a better light and definitely draw less current too. These LED-replacement globes come in all shapes and sizes so before heading off to your local retailer, maybe take a picture or make a careful note of how the bulb goes into the fitting – from the side, from the back – and also the space available for the replacement bulb. Better still, if you can take the whole light-fitting with you then you’ll be able to go through the options to find one that suits best.
In the post on Inverters we talk about Microwave ovens, and worked out a current draw of 110Amps at 12Volt for a 850W microwave. If that ran for just 5 minutes, that would take 9.2Ah out of our batteries (5min/60 x 110A = 9.2Ah), so 50% more energy than our 12Volt oven below. More importantly, the 12Volt oven’s 6Amps is no problem for our deep-cycle batteries, but 110Amps – whoa, rather not on my batteries thanks!
Yes, 12Volt ovens – if you’ve not yet come across the Australian-made Travel Buddy oven, then have a look around – and talk to the guys on the road – they’ll tell ya! It draws about 6 Amps when it’s going and has a timer which switches the oven off so it won’t keep flattening your battery. Cooking times vary depending if the food is thawed or frozen, but 60-90 minutes is typical. So if we use the oven for one hour a day that will consume just 6Ah from our battery (1hr x 6A = 6Ah).
The most common water-pump used in camper-trailers, caravans, motorhomes and so on, is the Shurflo 4009 12Volt pressure pump. It operates on a pressure-switch which turns it off when the tap is closed. These pumps draw about 5 Amps, and the time they run is usually pretty short, given we have to carry our water with us when we free-camp. The pumps can deliver about 10 litres/minute so it will happily drain a 100 litre tank, from full to empty in just 10 minutes – yikes! So even if we go overboard and say we’ll have the pump on for 5 minutes a day, that will consume less than half an Amp-hour – very, very little is the short answer (5min/60 x 5A = 0.42 Ah). Also, having the tap half-open will help reduce the water usage but won’t affect the current draw that much.
There are also so-called transfer pumps, which are usually submersible 12Volt pumps with a set of power leads so it can run off a 12Volt battery. These pumps can be used to transfer either diesel from a jerry-can into a fuel tank, or to pump water from a creek into the caravan’s tank, and so on. Typically they are not self-priming, so they can’t suck up liquid in a pipe, but once they have liquid in them they can shove that liquid many metres high at rates from 15 to 30 litres a minute. So a 20-litre jerry-can will be done in a minute or two. They also draw around 5 Amps at 12Volts and because of the very short run-times power usage is usually not an issue.
Ok, on this one, the best I can do is to say that it varies – a lot. Every situation is so different to the next that it is simply not possible to estimate the energy that Bilge Pumps draw from the battery. The only sure-fire way to get a fix on how much the pump is using, is to measure it for your situation.
If you have access to a DC power-meter, then you can measure the daily Amp-hours directly and also get an average over a good few days to take into account weather changes, etc.
The measurement could also be as simple as seeing how long it takes to partially flatten a battery – so fully charge a 12Volt battery and let it run for a few days and then see how much it’s taken out of the battery. For instance if a 100Ah battery is connected to run the bilge pump and after 3 days it is down to 70% of its capacity then it has used about 30% of the battery’s capacity. So 30% over 3 days is about 10% of the battery each day, so the pump uses about 10Ah a day (10% of 100Ah = 10Ah).
LED TVs have been around a while now, and the whole of Australia is on digital TV too, so there are now a whole range of TVs that are quite happy to work off 12 Volts. A typical 24-inch TV will take about 3Amps from the 12Volt supply, so if we have that going for about 5 hours a day, that will draw 15Amp-hours from our 12Volt battery (3A x 5hrs = 15Ah). Have a look on the back of the TV or in the manual to see how much your actual model is drawing, as some of the bigger ones can be 5 Amps and beyond.
 The Australian supplier’s website has some pretty persuasive pictures showing how things can go wrong. The blankets they supply are both USA-made which is a fairly good indicator of quality.
 There are 12/24V air-cons but they draw huge currents – 30 Amps and up.
 This is the so-called “ice-cold-beer” temperature, but things at the bottom of the fridge may start to freeze.
 Plasmatronics solar regulators can measure the Amp-hours too, by running the pump off the Load terminals (ensure the pump draws less than the Load terminals can handle).