Hi guys thanks for all your help with the interent it was great and I feel that it is under control now.

Slowly working through the problems before hitting the road.

I have a 12volt fridge which draws 4A on 12 volts. it works well both as a fridge or freezer.

I went and brought 2 /12 volt batteries and I have them connected in parallel, I have a solar panel which a friend gave me which is old but works well and is 68w, the batteries charge up fine during the day and the fridge runs great but it will not last the night, the fridge has a cut off if the batteries reach 10.4v and during the night the batteries run out of juice and the fridge switches off.

Surely with 2 batteries it should be enough to keep a fridge going over night.
Any help with what I'm doing wrong would be appreciated.

Graeme

Yep Graeme, theres  a problem

If the batteries you purchased at say 80aH each, each one of them should supply 4amps for 20hrs, without recharge, so with two it should be 40hrs run time.

But even this is not right, as the fridge should not run continuously, maybe only 50% of the time, meaning you should have 80rs run time.

The solar panel, though rated at 68w, will deliver less than this, particularly outside of full summer sun. Even if you derated it by 50%, and allowed for 6hrs charge time, it should charge the batteries with approx 16amps

So I would check to ensure you have the batteries connected in parrallel correctly. Also if they are new, a first full charge by other means may be in order, to bring them up to full capacity. I would also check that the fridge is cutting out - cycling

Thanks TwoBob

I will check all you have said and put both batteries on charge, one thing I didn'y say and not sure if this makes a difference the batteries that I purchased were just to 12 volt car batteries for a medium car not sure what Amp hrs they are they cost $149 each. Have I got the wrong batteries.

Hi Graeme....yes you need Deep cycle batterys...of at least 100 amp hour..normal car batterys produce power to start car up....my 120 amp hour battery cost me about $230 ...and is totally sealled..


Dave

Deep cycle batteries are the best for this situation, but, normal car batteries will do the job.

A standard car battery, and do not quote me, I think is about 50ah. They normally are rated at cranking capacity CCA? While not meant for this task, can be used.

In fact I have used a couple of heavy small truck batteries, rated at 78ah, to undertake an scientific experiment. They were only needed for 6 months, and did the job. Daily total discharge and full recharge. Also they were then put to work as second batteries in vehicles, after.

So, if you already have them, use them. Just expect more maintenance of water level, and to replace them, earlier than a deep cycle one.

In fact I may go out on a limb here, expecting to be cut down. I would use a car battery before deep cycle, for part time use. The expence of deep cycle can only be justified for long term constant use. Where as a car battery can be put to use in the car, when not in use for its intended purpose. Basically rotating the batteries, and limiting the sulphating of the batteries.

All batteries deteriorate, when not used, and full of fluid (elecrolyte)

Graeme I would like some more info please, when you say you are running them in parallel please explain to me just what parallel means to "you". I don't want to make you out to be an idiot I just want more info somewhere on your batteries there should be some sort of numbers please post those for me so i can see what you bought grab a multimeter and do some "tests" for me please. these meters can be bought from a dick smiths or similar for $20 I want to know the starting charge of your Batteries individually, I want to know the output of your solar panel when in full sun and I want to know your finishing charge when the sun goes down after charging, i also want the combined output rating of your parallel battery setup separate the battery's and run the fridge (already cold) on one battery, see if it flattens just that one then run the test again on the other, just because they are new doesnt make them not faulty if you have the batteries connected correctly and fully charged then you will have sufficient power to last several days without recharging the lead acid battery is fine for what you are doing, dry cells better but cost prohibitive in comparison i have run "wet cells" for years (2 x 100 amp) without any trouble when you say you have a 12 volt fridge is it a thermo or compressor type, a thermo will run constantly and will quickly drain your battery's