Inverters for Caravans and Motorhomes

 

Almost every motorhome and many caravans use an inverter. These clever electronic devices take the low voltage direct current (DC) power from our batteries and convert it to the same high voltage alternating current (AC) that our household sockets deliver.

This allows us to have 240 volt mains power with us no matter how far we are from the nearest power point.

Selecting an inverter

When selecting an inverter, you have two major decisions to make … capacity and waveform.

 inverter_trace

Capacity

Capacity is easy to understand so lets deal with that first. An inverter that is rated at 1500 watts will run 240 volt appliances up to a total of 1500 watts continuously (not just for 5 minutes). The surge rating so often quoted in flashy eBay adverts for inverters can be largely ignored. This is the amount of power that the inverter will supply for a second or two only. Many appliances require larger quantities of power at start up. This ability to cope with surge current allows these appliances to run from the inverter. Almost all inverters are happy to supply twice their normal rating for a second or two.

When considering your inverter capacity, keep in mind that generally speaking, the larger the inverter capacity, the less efficient it will be when you use it for small appliances. For example: If 1500 watt inverter is quoted as having a peak efficiency of 90%. This 90% efficiency will most likely only be delivered when the inverter is delivering 1300 watts. If you only require 300 watts from the inverter its efficiency may fall to just 60%.  In practical terms, this simply means that you should always select the smallest inverter that will meet your needs.

Consider as well that there are (as always) no free lunches … if you install a 6000 watt inverter and plan to use it at full capacity, you are going to need a trailer load of batteries or a portable nuclear reactor to be able to keep power up to it. A 6000 watt inverter will require at least 250 amps at 24 volts to deliver that 6kw (or 500 amps at 12 volts). This would completely deplete your 200 amp hour battery bank in less than 30 minutes.

As a general guide, an inverter for motorhome will probably fall into the 800w – 1800w range.


Wave Form

Pure Sine WaveWave form basically describes how closely the inverter matches the power that you get from your household power socket. Inverters fall into two distinct groups: those that produce pure sine wave power, and those that don’t. If the inverter that you are looking at does not say “Pure Sine Wave”, then there is a very good chance that it is not.

Inverters that are not pure sine wave are often described as one of the following:

  • Modified sine wave
  • Modified square wave
  • Quasi sine wave

Pure sine wave inverters are typically more expensive to manufacture and accordingly more expensive to purchase. This gap has narrowed considerably in the last few years.

There is nothing wrong with inverters that produce something other than pure sine wave. They work just fine with the majority of 240 volt appliances. But the key word there is majority. There are a growing number of devices that will simply not function when asked to use anything but a pure sine wave. Some devices will instantly self destruct.

We have an excellent Trace brand 1500watt inverter in our motorhome. It produces modified sine wave power. A few months ago I purchased a fairly high tech soldering station. About 4 seconds after plugging this into the power produced by our inverter, it emitted that dreadful electronic death smell and promptly expired, never to solder again.

The battery charger that was supplied with my new camera lasted a little longer (15 minutes) before it went the same way.  These are the exceptions – I have run many other appliances successfully for years – but that makes the loss of these two no less painful.

We don’t often buy new electrical devices, but when we do it is with huge dread that I plug them into the inverter for the first few times.

My advice is to buy a pure sine wave inverter if at all possible and completely avoid this issue.

Other features

Chargers

Some inverters have battery chargers built into them. This effectively makes them work in reverse; when you attach 240volt mains power to the vehicle, the inverter switches to charger mode, stops converting low voltage DC into high voltage AC and instead charges you battery bank. This is often a very economical solution – an inverter/charger usually costs a lot less than an inverter and a separately purchased smart charger. 

Remote control

It is likely that you are going to want to tuck your inverter out of sight somewhere. A remote control lets you turn the device on and off and perhaps get status information from somewhere more convenient.

Auto Start / Standby

This is a very useful feature that saves battery power by putting the inverter into a kind of sleep when 240volt power is not needed. It negates the need to manually turn the inverter on and off when required. 

Solar Regulator

Some inverters go one step closer to a “one-device-does-all” by adding a regulator for your solar system.  I am personally not a big fan of this approach, preferring to use a dedicated solar regulator.

Safety

Don’t think for one second that the power produced by an inverter is any less lethal than the stuff that invisibly leaps out of the mains system and kills people. It is exactly the same stuff and can inflict the exact same perhaps fatal shock.

 Inverters

Inverters use large amounts of power, they therefore need heavy cables and very good quality connections. An inverter that is drawing 100amps from the battery will melt a small cable in a few seconds – a loose connection will become very hot very quickly. When installing and wiring an inverter take great care to get every connection tight and secure.

Summery

  • Buy an inverter that is large enough to meet your needs but not over capacity.
  • Select a pure sine wave inverter to avoid issues with some appliances.
  • Wire the inverter with the correct sized cables and make sure every connection is 100%
  • Treat the power it produces with the greatest respect.

 

:-)

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15 Responses to “Inverters for Caravans and Motorhomes”

  1. John Says:

    Additionally to the advice to get a pure sine wave inverter to ensure compatibility with appliances, is the effect on batteries. The supplier of my deep cycle batteries provided a 5 year warranty, reducing to 2 years if a modified sine wave inverter is used! Apparently there is some effect working backwards to the batteries.

  2. Hobo Says:

    That’s interesting John. What brand of deep cycle batteries are you using.
    I am guessing that the “lumpy” nature of modified sine wave inverters has a negitive effect on the batteries that supply them. This is the first time I have heard of a battery manufacturer altering the warranty.
    Thanks for the info.

  3. John Says:

    They are Champion AGM, supplied by AA Solar here in NZ. The warranty is pro rata after the first year. Cheers.

  4. Caravan Man Says:

    Do you have any particular brand thats good? Would a chinese made inverter be a worthwile investment?

  5. Hobo Says:

    There are a number of well respected brands – Xantrax would be my favourite (American made). My brother-in-law has just purchased a Chinese made inverter from eBay. It is well specified and I will be installing it in the next few weeks. I will report on this inverter once we have had an opportunity to test the unit.

    Hobo

  6. john Says:

    hi there guy’s
    hope u traveling well
    need some help with inverter problem
    bought new and put in bus

    Continuous power: 2500W
    Peak power: 5000W
    Input voltage: 24V DC
    Output voltage and frequency: 240V AC, 50Hz
    Output wave: modified sine wave
    Efficiency: > 90%
    Static current: >??
    and i didnt think this small unit would damage inv

    am i wrong???

    plugged fridge back in
    voltage came back up to 240v
    unplugg and drops to 160… 180
    fans never came on before even when running fridge all day

    now they on all the time

    ah well live and learn

    buti thought this size would have been ok for what we needed

    any ideas
    cheers

    john

  7. Hobo Says:

    Hi John,

    Firstly I don’t think the size of the inverter can be an issue – 2500w should have no issues starting and running a fridge. Also I would not be too worried about the low voltage when there is no load on the inverter – some inverters do this to save battery power. They immediately push the voltage up to normal once they see a load.
    Modified sine wave output may be an issue – some electrical items do not like the abrupt changes in the wave form and it can place a greater stress on insulation (particularly on appliances with motors). There are also electronic parts in most fridges that could be damaged by the Mod Sine Inverter (My mod sine inverter destroyed a brand new camera battery charger in about 10 seconds).

    Some things to try …
    - Try running the fridge from a mains socket – does it still run ok? If so, then the inverter has not damaged it.
    - Put a small load onto the inverter (60w light) and see if the voltage is stable and if the fans come on.

    I know that there are a huge range of very poorly designed and built inverters coming out of China (I have first had experience with one of them) – they are just rubbish.

    Please let us know how the issue progresses.

    Gavin

  8. john Says:

    ok i think u only got half what i typed,,some missing
    wife bought a small hand vac,i said we try incase it fries it on inverter
    240v 600w little dust buster type
    this what did the damage,fridge was fine
    been aguing all day with emails from company.they say it was to much for inverter
    i agrue that there specs say overload protected at 5000w.. which is not
    his replay was that is surge protection to 5000w
    but thats not what it states
    i realise that start up is a lot more ,but 2500w continuos ???
    company in melb but hold little hope
    he agrued it could pull as much as 4000w when running..not just on start up
    therfore void warranty
    i know a fair bit about motor ramp speeds as i use them a lot at work when setting up speed controllers
    and i cant see a dust buster pulling 16 amps when running
    any way ,lost cause i think

    your tracking devise working well
    hope u have a safe trip

    cheers john

  9. Hobo Says:

    Hi John,
    Sound like you are getting a raw deal from the company who sold you the inverter. There is just no way that a 2500w inverter could be overloaded by a small vacuum cleaner … here is why…
    1. A standard household power outlet is rated at 10amps – that is 2400watts. If the vac overloaded a 2500w interter, it would overload a standard 10amp household socket.
    2. We run a full sized household vacuum cleaner (1400w) from our 1500w inverter – no problem.
    3. Vacuum cleaners use series wound motors – these do not surge when started (which is why we can start and run a 1400w cleaner from our 1500w inverter).

    I get very upset where I hear of companies that import rubbish from China – then refuse to honor the warranty. Feel free to name the company and brand of inverter as a warning to others.

    Gavin

  10. john Says:

    On 24/05/2010 11:09 AM Michael wrote:

    Hi,

    Thevacuumneeds around 4000W to run – 600W it’s the suction power, not the powerit needsto run.

    Runningiton the inverter probably damaged it and that’s why it plays up …

    Best Regards,

    Michael B

    Sales Manager,

    Bit Mb Pty Ltd, Melbourne

    On 24/05/2010 11:56 AM Deals wrote:

    5000Wis only protection surge –you cannot run anything bigger than 2500W on it

    Best Regards,

    Michael BFrom: Michael
    To: jmphilip@bigpond.com
    Sent: Monday, May 24, 2010 1:16 PM
    Subject: RE: RE: RE: hi

    It sais very clear in the manual – for item with electric motors you have to multiply by 7

    600W X7 is 4200W

    This inverter is 2500W – also very clearly stated in the manual NEVER to run anything bigger than the continues power which is 2500W

    The duration of the protection is a lot less that the duration of starting power

    This is not under warranty, warranty cover for manufacturer faults, not for damaged items.

    We can check it if you like, that’s not a problem, but I doubt it’s a warranty problem

    Best Regards,

    Michael B

    thers the info gav
    hope u read
    ebay name
    bit_deals

    is up to you wether u put there name there
    i dont want u in the shit

    To: “Michael”

    on a better note
    i boguht a pure sin wave to do part off bus
    tv comp etc
    all i need is one for fridge which i will get soo

    so 2 seperate systems

    maybe better in hind sight

    kk safe travels to you and tracy
    se you on the road some where

    cheers

    john & marl

  11. john Says:

    ok things seem not to be missing when i type here??
    seems like only half the text being saved>>

    kk just sent his email
    because was missing from last reply

  12. john Says:

    and aagin deals@bitaudio.com.au>

  13. Chris Brand Says:

    haha, I bought an inverter off Bit_Deals as well. 3000w continuous and 9000 Peak Pure sine wave. It stopped working after a few months. Trying to get warranty but they are not responding to emails. Im sure its from china as well but it doesnt look cheaply made. Weighs 22kg. I realise this is an old thread but when its on the web its there forever.

  14. Chad Says:

    600w inverter instructions say not to hard wire it to the battery and to not have it connected to a battery if using a battery charger. The caravan naturally has automatic battery charger when connected to mains. Should a switch be installed between battery and inverter? Or is the switch on the inverter enough protection?

  15. Hobo Says:

    The only reason I can imaging that they specify this is that the inverter is not tolerant to the voltage applied to the caravan battery when charging or perhaps it can not handle the small ripple that some chargers apply to batteries. I’m guessing a low cost inverter??? If this is what they specify, I would suggest a switch on the DC input side of the inverter (between the battery and the inverter) would be the best solution. It does beg the question – what about charging from a solar panel (something we all do when using our inverters every day)???

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