So you take decided that you need to run some mains powered equipment when away from home and your caravan or gunkhole is not plugged into an EHU or Shore Power.

Before we expect into the options for inverters and what to look out for, nosotros have to ask a few questions starting time. What are we wanting to power? If it's that you need to charge your mobile phone or laptop, then maybe an inverter is not the best way of doing it. At that place are a number of manufacturers offer a wide range of products for charging your mobile devices. An older manner phone may demand a dedicated 12 volt charger, but modern smart phones can usually be charged via a USB port and there are a number of products that offer USB charging from 12 volt 'cigarette lighter' type plugs. For laptops, it's a bit more difficult, but in that location are options. Companies such as Lenovo, Kensington and Targus offer such devices. I accept not put any links in as manufacturers often update their sites simply you can search for them as "Universal Auto/Air Laptop Charger"

So, you nevertheless need an inverter?

Well, there are three principal categories of inverter – Compact or Lightweight, Heavy Duty and Inverter/Charger. The compact or lightweight inverter is one that will ordinarily plug into your 12 volt accessory socket in the car, caravan or boat. Compact or lightweight are usually rated up to about 200 to 300 watts and because of the cost are usually of the modified sine wave type – read through Understanding Inverters to go to know the unlike types of inverter and how they work. Call up, only inverters with a rating of 180 watts should be plugged into your accessory socket or you risk exceeding the fused current rating.

I'll skip the second type for the moment and go on to the Inverter/Charger blazon. These are probably more commonly known every bit a UPS. No, it's not one of the dark-brown short wearing packet delivery guy'south…. UPS is Uninterruptible Ability Supply. Pocket-size UPS's are more usually constitute sitting under desks in offices and larger units in network and server cabinets. These are bits of equipment that plug into the wall socket and a computer plugs into them. They ordinarily have a set of batteries internally and are designed to proceed a  computer running for a short while in the upshot of a power cut. Some have the option of adding additional external batteries. UPS's are swell at running computers for a brusk period of time as the demand on them is fairly abiding, they besides have additional technology that volition keep the output voltage stable and clear of transient spikes even if the supply voltage varies. To make them more efficient, usually they have 24 volt or 48 volt internal batteries, this allows the employ of physically slightly smaller batteries for any given run fourth dimension. The internal circuitry also monitors the batteries condition and will charge/discharge them in a maintenance bicycle.

The device we are really interested in is the Heavy Duty inverter. These are available from 750 watts right up to 5000 watts – but at this wattage, just expect your 110Ah leisure battery to terminal a few minutes!

We decided that it wasn't a mobile phone or laptop that nosotros needed to charge, and so what is it you want to run? Well, it could exist anything… and the about mutual matter that people want to power is………… a hairdryer, closely followed by pilus straighteners.

Well, we need to find out what size inverter we need to run our hair intendance devices. If we look at a hairdryer, information technology will have the wattage for the appliance written on information technology, lets say 1200 Watts for a professional hairdryer. When it'due south connected to the mains supply, that 1200 watt's is about 5.2 Amps ( P /Five = I or 1200 / 230 = 5.2 ) which isn't besides bad. And so how much will that be out of our 12 volt leisure bombardment? Well, 1200 watts is 1200 watts, no matter what the voltage, then we can do exactly the same calculation as before: 1200 Watts / 12 Volts = 100 Amps.

"Wow 100 Amps! That's near what my car takes when starting!"

Yep, we are talking big bits of wire hither. Now the calculation above would be swell if some of the laws of physics didn't exist and inverters were 100% efficient. Unfortunately they are not, far from it. It's safe to presume that as an average they are round virtually 80% efficient, and so nosotros need to take that into account. It is e'er improve having a 2000 watt inverter running a 1200 watt load rather than a 1200 watt inverter running apartment-out. Then, looking at our 1200 watt Hairdryer, we demand to think of the 20% loss using the inverter, so we add together another 240 watts and we accept a load of 1440 watts. We need to be looking at that 2000 watt inverter really. If you are going to brand the investment installing an inverter, it's ameliorate to make sure you go ane that will be comfortable doing the chore.

Inverters of this size need installing permanently. The maximum current a 2000 watt inverter can describe is 166 amps… in fact it volition be a fleck more as the inverter itself needs power, normally to run a couple of cooling fans and its ain internal circuits. The 12 volt cables that connect it to the battery are going to be as thick as your index finger, so some conscientious planning on its location is required.

So we have decided on the size of inverter, now what else?

Pure Sine Wave -v- Modified Square Wave

For me, at that place is no competition, always go for the Pure Sine Moving ridge. Information technology will exist more expensive but y'all tin can be sure it will ability absolutely everything you plug into information technology. Modified square wave e'er have a nasty addiction of powering some things, but not others and information technology can be really annoying. In addition, some kit tin be damaged if you lot try running of a modified foursquare wave supply. If you are not sure what the divergence is… it'southward all explained in Understanding Inverters.

Inverter Efficiency

Sometimes bigger is not improve. What nosotros really need to know is what percentage of the ability that goes into the inverter from the battery comes out the other side as AC ability. To brand this calculation even more than difficult, the efficiency of an inverter changes with the output load placed on it. if a small load is put on an inverter information technology may be simply effectually l% efficient. However increase the load to about the inverters stated maximum continuous load and the efficiency volition rising to effectually xc%.

A 3000 Watt inverter may depict effectually 20 Watts of ability from the battery when information technology is continued and turned on without anything plugged into the output. This power is what the inverter needs to run itself… battery monitoring circuits, alarm circuits and peradventure a small fan. Now if we plug-in a small Air-conditioning load.. say xx Watts…. the total load on the battery is now 40 Watts (20 for the inverter +20 for the load) and then a chip of maths – xl watts in – xx Watts out shows an efficiency of 50%.

Now if nosotros expect at this again with a small 150 Watt inverter – connected to the battery with no load it takes about five Watts to run the inverter. Now if nosotros plug in the aforementioned 20 Watt load we have 5 Watts for the inverter plus 20 watts for the load giving a total load on the battery of 25 Watts. So 25 Watts in and twenty Watts out gives united states of america an efficiency of around 80%.

Practically this means that you coud run your 20 Watt appliance for much longer on the same battery by choosing to utilise the 150 Watt inverter rather than the 3000 inverter.

So size does matter…. but bigger is not always better. Matching your inverter size to your load size to maximize your run time of a battery is important.

What else?

Well, await for some of the post-obit features:

  • Depression voltage warning
  • Battery car cut out
  • Over temp alarm/cut out
  • Remote control
  • Ability relieve sleep mode

The depression voltage alarm is a must have actually. It will warning you when the voltage on your bombardment has dropped to a level that could starting time to permanently impairment your bombardment by allowing information technology to belch likewise much. On some models, this voltage tin can be set differently for the type of bombardment you lot are using.  The Battery motorcar cut out will shut downward the inverter when this critical voltage has been reached. As an inverter of this size is handling a big electric current, some of the internal components will get very hot, It is therefore essential when installing information technology to pay particular attention to the manufacturers installation instructions to brand certain its located correctly. Well-nigh all proficient inverters will accept an over temperature warning and cutting out that will stop your inverter being damaged if information technology does get likewise warm.

The next two are "dainty to accept's"… when your inverter is switched on, fifty-fifty if in that location is aught plugged into it, it volition consume precious battery power. It can be as much as ii or 3 amps. Some of the more sophisticated units take a slumber manner, which means you can leave it turned on and it will only consume a few milliamps…. until a load is plugged in. Some units don;t have this, instead, they accept a remote control that allows you to turn on the inverter without having to physically printing a button on the unit of measurement. This allows some flexibility in the location when installing it.

If you lot are installing an inverter in your caravan, motor home, boat or RV then make sure to follow the manufacturers instructions. Try to install the unit as close as possible to the battery to keep the big cables as short as possible and brand sure you lot install an isolator switch and fuse between the inverter and battery. Modern leisure batteries store an unbelievable amount of free energy that if discharged quickly tin can have a catastrophic outcome and tin can impale. As with anything electric… if you lot don't know – ASK and stay safety.

Inverter Current and Power Table

One of the most oft asked questions I get is "what current volition be fatigued from my battery for a XXX watt device plugged in to my inverter?"

To make it simple, I take assumed two things:- I, the rating the manufacturer gives is the inverter INPUT rating so a 300 Watt inverter is actually a 300 Watt input, not output. The 2d is that the efficiency is 80%.

So if you have a 300 Watt appliance yous desire to run, await downwards the correct hand cavalcade (Output Wattage) for 300 Watts…. as there isn't one for 300 Watts go to the next line – 320 Watts. Now look across to the left manus column (Inverter Rated Wattage) – 400 Watts. This is a good starting betoken for the size of inverter you lot would require.

Click on table to view full size

Click on tabular array to view full size

As we accept seen before, some inverters are more efficient, some less dependant on the load, so the table doesn't account for that. Also, some equipment has a higher starting current at switch on than when running, again the table can't piece of work that out for you, simply it does give you a proficient starting bespeak. If you lot think you know which inverter you desire, check out the manufacturers specifications on-line. Almost publish full details, including temporary top loads – which is useful to know if yous anticipate using something that has a college starting current.

Superlative Tip

If you desire to use an inverter using two batteries to provide extended run fourth dimension, read my  "How To: Connect 2 Batteries in Parallel"  as at that place is a right way and a incorrect mode.

I hope you establish the guide useful, proceed looking out for some of my other guides here on Caravan Chronicles

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