The Caravan Owners Club

[Hobbynut]

My 710 has no 12 volt fitted which is inconvenient if I get a power cut on site. Whilst talking to a friend who has very large canal long boat he told me that all his 240 volt is not supplied by generator as I thought but by inverter which runs off a 12 volt battery but gives mains voltage. As a result of this and with a bit of research and and some help from e-bay I bought a 750 watt inverter. I can now plug my mains van lead into the inverter, connect the inverter to a 12 volt battery and and my van lighting, fridge, tv etc will now run without being conected to the mains. How long will the battery last doing this?...I haven't done full tests yet but connected to my car battery for 1.5 hours, the car then started no problem at all..The inverter cost me £38 pounds off ebay and this whole set up does exactly what I want it to do...Please note not powerful enough to run fan heaters or kettles. Hope this might be of use to someone..
Chris Bennett...Hobbynut

[Chubbs]

I am sure someone will correct me if I am wrong, but I believe the discharge rate of a leisure battery makes it less suited to use with an inverter than a car/lorry battery. They are designed differently internally. So if you use an inverter it is better to use a conventional car battery.

How long will it last? Theoretically an 85 Amper-hour battery should deliver 12 volts at 1 amp for 85 hours, or 5 amps for 17 hours, or any combination equivalent. i.e. 12x 85 Watt-hours or 1020 W-h

Using an inverter does not change the capacity of your battery so running a 750Watt inverter at say 100 watts actual continuous usage rate at 240Volts, your battery would last theoretically 10.2 hours maximum. (I.e. 1020 W-h divided by 100 W = 10.2 hrs). I think theu are about 99% efficient anyway.

So, divide the capacity of your battery(e.g. 12V x 85 Ah) by the wattage you are actually using through the inverter to find the theoretical maximum duration.

However, I don't think it is desirable to totally flatten any battery between charges.

Cheers.

[Doc]

Hi Chris and Keith,

Keith's analysis sounds about right, but the efficiency of the battery declines more rapidly as charge is removed from it, so you'll never get anything like the theoretical length of time. Won't do the battery any good to discharge it too much either.

I've always thought the caravan makers could learn a lot from the electric systems used in canal boats; my switch-mode charger is used mainly in canal boats.

I went round some at the NEC, just to see if there were any ideas that could be used in caravans, and their electric systems were far superior; many had built-in charger/inverter units. If you have mains supply then the unit charges the 12V batteries, and with no mains the batteries supply 240v mains via the inverter. Good eeh? Of course canal boats don't need to watch the weight, like caravans.

Then you've got susbsidiary battery charging using a solar panel. More of that later!

[Hobbynut]

Thanks for that information Chubbs that is very helpful.. The inverter I have got triggers off a warning signal if the battery voltage drops below a certain point. Its not my intention to run on inverter for a really long time.but its just with my 710 been semi permanently sited ( towing regs and all that ), the site is subject to more than its fair share of short duration power cuts. The inverter does the job perfectly and is no bigger than a half pound box of chocolates

[denjo]

Hobby dealer at adlington does the conversion for £285 all inclusive.

[n1cktd5]

Hi,
Have you had this 12v converersion done buy the Adlington dealer ? I am looking into buying a 540 UK in the next 2-3 months and a 12v conversion is top of my list, as we do a lot of rallies and only use 240v periodically.

Any help ould be good.

Thanks,
Nick