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atb

Wizard

        Can take  u take a spare battery ?. To run your tele and other things.I use a 300watt inverter .

Quote: Originally posted by mysty g on 22/6/2008

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        Can take  u take a spare battery ?. To run your tele and other things.I use a 300watt inverter .

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Our fridge is a 12v only compression one, a Waeco.
From the battery we also run 3 fluorescent lights, 1 torch and 2 phone chargers, 1 x 12v freeview digital box, 1 x 12v TV and a wired in 12v drill that I use with the Wurmi Pegs when we have the awning up. But, at the moment, because this last unit uses so much power, we only put the awning up when we are on a site with EHU.

The battery also powers the motor movers.

We have a 110Ah battery and a 55w Solar Panel and the manufacturers of our van reckon we will get 5 or 6 days power from the battery before it needs a boost from either an EHU or from being towed to another site.

However, I have an old Uni Charger which I am hoping to resurrect which will allow us to trickle charge our caravan battery from the car battery overnight and if I can get this working again, we will be completely independant of EHU altogether.

Thanks for the info all .

Could someone tell me what amount of amps i can expect to get from a 110 amp hour battery , i'm estimating about 85 / 90 .

I'm finding it difficult to work out how much stuff will use to amount of battery life .
I.E. if i run items that draw 50 watts an hour, how many hours will my battery last .

One other thing i'm having trouble understanding is , if say the battery is considered flat at 10.0volts, does the battery output the 85 / 90 amps between 13.6volts and 10.0volts .
If someone could enlighten me it would be a great help .

Thanks Wizard

One other thing , am i right in thinking that from a 12volt battery 1 amp would = 12watts .

So if say my battery produced 85 amps i would get roughly a 1000 watts of usable power .

atb

Wizard

Wizard,

perhaps the thing to do is to go to a site with EHU but not use until desperate.  Then you can try all these things out and get a definitive answer.

I think theoretical calculations on battery power can only give you a rough idea.

Two batteries would help plus car boot charging if you go out in the car during the day.

Volts x amps = watts therefore 1amp at 12 volts requires 12 watts.

I have a 300 watt inverter. They are quite noisy. If I was going down the 12v route and wanted a TV I'd get a 12v to run direct from the battery, more efficient.

The inverter will cut out when the voltage drops, usually when the battery is about 50% discharged, so as JTQU says on a 110 aph battery you've got a maximum of about 55 amps which is only 660 watts.

You menton the Sat box, 1 amp - I assume that is on mains, so equals 230 watts? Seems a lot, but I don't know much about them.

Hi Wizard

Check how many of your appliances are actually 12v with an external mains power supply. Charger for the phone for instance, use a car charger, they use next to no power. Tesco flog these for less than £2 now. Your TV and sat box are probably 12v and could be run straight off the battery- see the back of the appliance. This is far more efficient than an inverter system. An inverter is at best about 80% efficient (rest goes in heat) mains power supplies can be anything from 60% to 90% efficient, so combined you are only getting an efficiency of about 50%, ie losing half the energy. 

 There is a limit to how big an inverter you can use. A 300 watt inverter would draw about 30 amps on full power (allowing for efficiency rating), far too much to plug into a cigarette lighter socket which are rated at 10amps. It would have to be directly wired to the battery. On full power, your battery would last just over 3 hours. It may well shorten battery life at this continuous current.

37 watt TV = 3amps/hour on battery, would last about 35 hours on a 110ah leisure battery.

Also, don't forget space heater and water heater will also use your 12v in their control systems. Add on such things as water pump usage.

Of course, you could leave the TV at home....

A fully charged leisure battery should be around 12.8 -12.9 volts and you can run it down to about 10 volts. Lower than that and the caravan charger will not recharge it, you need a special battery charger to recover it, and they usually take 24-36 hours to do the job.

You might find your space heater (assuming it is an inbuilt unit and not a simple gas heater) and water heater cut out as the battery voltage drops, even though they are running on gas.

We use our laptop as a TV/DVD player, this works great off 12v. However we use it an average of 1 hour a night. It has a battery life of 4 hours and can also charge up in the car when we go out. We can last a week on battery no problem, even with the motor mover. Its well worth it, from cost of EHU and also availability of non-electric pitches at short notice (and when I accidentally book a pitch without EHU).

Our caravan did not have one of the crude battery meters fitted so I bought a 4 digit voltmeter display off Ebay, fitted it in a small box with a switch and shoved it in a cupboard. Cost about £20. Accurate to 100th of a volt so easy to see how well battery is lasting, and whether it is charging correctly (voltage rises to 13.8v when charging). I aso keep a charging lead in the car so if we go out for the day, the battery can go in the boot and charges up while driving.

Now how about campaigning for all campsites to offer battery charging facilities...

Martin    

Great advice thanks , never realised that i'd only get 55amps from my battery before doing damage , have to bear this in mind , how would i know when i've used 55amps , is there an easy way of checking ?

My sat box is 1 amp at 12volts ( just found a lead for it to run off a cig socket ) .
I've just sold my 300watt modified sine wave inverter on ebay because of the buzzing , and bought a 300watt puresine wave inverter , i'm hoping this one won't buzz and will produce better AC mains for our flat screen .

I do like the idea of a second battery stored in the boot , i should be able to work out a way of 'plugging in' to the caravan with out taking it out of the boot .

Thanks Wizard