deep cycle batteries

Hello mongrel,

if it's a small 240VAC fridge, it'll probably use somewhere between 0.4 and 0.8kWh per day.
You get a good indication of this if it's fitted with an energy rating sticker.
A 12V 100Ah battery would be just within range. Albeit it might struggle a bit at the higher end of 0.8kWh/day.
That is, if you only recharge once per day.
If you recharge twice in the morning, and evening, things look much better.
It might be feasible to put 2x100Ah battery to work, because then the recharging times are shorter, not only because your max peak charging current can be twice as high. The absorption stage is also shortened if the battery gets discharged less.
For the fastest high current recharging times, select pure lead/tin spiral wound AGM technology which allows for the quickest recharging times.
Pure lead/tin also can stand PSOC conditions a lot better than any other alloy.

Have a look in my profile to find out more.
Any questions, just fire away.

Best regards, Peter

Hi there. It's a bit hard to reply without knowing the power requirements of the bar fridge. But let's estimate that it draws about 1 amp at 240v (ie 240W). That's about half way between a caravan 3 way fridge and a 240v household small fridge.
Through an inverter, assuming the inverter is 80% efficient, that equates to 24 amp at 12v draw on the deep cycle battery. So a 100 AH battery would be down 50% (ie flat) in 2 hours and beyond repair in 3 hours!!
Unless I have stuffef the maths, then I suspect your idea may need revisiting, or else you'll be running the genny most of the time, which isn't nice for you or anyone around you.

Hi Ross
an inverter is a very innefficient way of running anything let alone a fridge that will be no doubt running non-stop. To answer your question, i would suggest hooking up your fridge to the inverter (i would get it to running temp on 240v first), put an amp meter between the inverter and the battery and measure how many amps are being drawn, then wait for the compressor to kick in and measure it again. The answer may surprise you as it will probably be quite high. A 100amp hr battery in theory deliver 100 hours of power at a current draw of 1 amp. I am under the understanding to protect the battery that you shouldnt drain it by more than 50% SOC (state of charge) which i believe is around 12.1 volts. i am also under the understanding (someone will correct me if im wrong) that therefore this halves the running time to 50 hours (based on a 1amp draw). Different battery types have different levels of tolerance to this, usually the dearer you go the better the tolerance. But knowing the amp draw and the intended run-time of the fridge would be required to answer the size of the battery required.
I would only guess but the fridge may draw up to 6-10 amps when the compressor kicks in, this would not give you much run time. Also will your inverter handle the fridge at full power ie compressor going in terms of its constant wattage (not peak)
The generator is also a very inneficient way of charging your battery especially if it is under load at the time when you are charging it (unless you switch to running the fridge straight from the genny whilst you charge).
I would personally consider a solar panel to keep it somewhat topped up during the day, then the genny wont have such a big job to get the battery up to full.

If you had the spare money, i would reccomend a small 12v\240v compressor fridge such as a waeco, engel or ARB (just examples), a 100ah battery and perhaps consider hooking it up to the car to charge whilst you drive via an isolator. i know that wasnt your question, but my opinions are free, and if you dont like them- i have others!

good luck with it!

Ross,
Is there a reason why the battery won't be connected to the vehicle for charging when your traveling ??

As others have said you have to know the fridge power draw befor an answer is given, unless you want guess work replies.

Maîneÿ . . .

Hi Ross, Iused an 80L bar fridge in my van & ran it of a 240V inverter when travelling it pulled 12Amp of the battery. When stoped used a generator till we went to bed then switched it off till morning. Eventualy went to a Waeco 80L upright fridge which draws 6Amp of battery, much more eficient & more than happy. Only using an N70ZZ battery on van A frame & charged buy vehicle altenator or battery charger if 240V avalable. Daryl

Ross the only practical way to power the fridge on 240V while travelling would be to have a 600W (minimum) sine wave inverter in the vehicle and run 240V across to the fridge in the caravan. The sine wave inverter would need to be connected to the vehicle battery using a Redarc SBI12 Battery Isolator. Attempting to power the 240V fridge any other way would be a short term disaster.