Amp hours is the measure for deep cycle, start batteries CCA. Deep cycle batteries have thick plates, not designed to give lots of power quickly as a start battery. What are you wanting the batteries to do!
meathead_timaru,
Dec 31, 4:21pm
Oh, and the Amp-hour rating is based on 20 hours, not 1 hour. So a 65Ah battery can deliver 65/20A continuously for 20 hours or 3.25A (nominally 40W). Going beyond that will shorten their life.
jacqui248,
Dec 31, 5:05pm
hi there
Its only 7 days! wen we are camping.
im thinking if it silghtly short. a, im gonna have a older back up battery there, and B, we do not plan to open the fridge much, once twice a day, will hae a shilli with ice also for stuff we need get lots ina day.
So with that in mind as long as it goes whilst the sun is shining ie battery gets charge via sun and if it dies at night, its cooler anyway and will crank back in when sun comes back out im thinking it will still work efficently enough! am i right or way off track here!
jacqui248,
Dec 31, 5:07pm
i dont have the inverter yet so cant try it out just yet.
Can i have two batteries charging off the solar panel! how would you do that! two lots wire coming out of panel to each battery, OR 1 wire going panel to first battery and then more wire going first battery to 2nd battery!
matarautrader,
Dec 31, 5:45pm
Your 85 watt fridge will draw about 7 amps from the battery. Your 80 watt solar panel will deliver about 5 amps on a stinking hot cloud free day but only for 8 hours max. So your battery will be flat in about 1 day. If its raining with no sun the battery will only last about 8 hours. Batteries cannot be completely discharged. Once the battery gets down to about 11.5 volts its reached its limit.
meathead_timaru,
Dec 31, 5:58pm
Yes, it will run less during the night due to the lower rate of heat transfer because of the lower temperature differential.
I would say since it's just for 7 days you'll probably be OK on charging rates with the 80W panel but the battery will need charging once you return. I presume you've got a charge regulator too or it's built-in to the solar panel!
As for a second battery, it depends on which inverter you opted for after the auction - the 12V or the 24V. The 24V model would require two batteries of the same capacity and condition. But again, the limiting factor is the ability to charge them as fast as you're using them anyway, which doesn't really change by adding another battery.
12V is more suitable for you - you'd only want the 24V with higher draw, like 200W+, where doubling the voltage halves the amperage, meaning smaller, cheaper cables and less draw on each battery making them more efficient.
If it were me though, for such a short duration, I'd just take another chilly bin and save all this hassle.
You're forgetting that the fridge does not run 100% of the time drawing 85W. More like 25-35%. And you can't estimate the time the battery will last without knowing its capacity.
jacqui248,
Dec 31, 7:11pm
ok i bought a 12 volt inverter.
so with no sun at all. if i got a 70ah battery. how long will that last roughly
Approximately 25 days continuous operating time using 9kg gas bottle!
thejazzpianoma,
Dec 31, 8:52pm
What is the make/model of your refrigerator! We are only guessing unless we know the duty cycle of the fridge etc.
In general though, attempting to run any fridge designed to run on 240v off a battery and 85w solar panel is not going to end well.
Better to start from the beginning with either a gas fridge or at least one designed for 12v use, they use a different kind of compressor and have better insulation which makes a huge difference.
jacqui248,
Dec 31, 9:20pm
samsung srg059 49 litre mini fridge
tmenz,
Dec 31, 11:00pm
Firstly, 0.7Amps at 230Volts is 161Watts, so there is a discrepancy between that and 85Watts. The published specification for annual energy consumption for a Samsung SRG059 is 321kWh, so the average hourly rating is 321000/8760 = 37Watts. Taking this average, the daily consumption is 37 x 24 = 890Watt.hours. This equates to 990Watt.hours of battery power with an inverter efficiency of 90% A 12Volt battery that can supply this for a day will need an Amp.hour rating of 990/12 = 83Amp.hours (all figures rounded off). To keep the battery charged up fully, a charger will need to supply those 990Watt.hours over a 24 hour period. If a solar panel has an average efficiency of 20% over a 24 hour period, (probably optimistic), then it will need to have a peak capability of 990/24 x 5 = 205Watts. Your 80Watt solar panel falls well short of this so it will not keep pace with the fridge's power drain and will not keep any battery or any number of batteries charged up. How quickly the battery goes flat depends on the initial size/capacity of the battery. For the aforementioned 83Amp.hour battery, it will probably go flat over a couple of days with the charger connected.
tmenz,
Dec 31, 11:01pm
Probably less than a day - see above.
a.woodrow,
Dec 31, 11:04pm
Perhaps another option if noise isn't an issue would be to get a cheap petrol generator from the likes of supercheap to run it during the day, and run on battery power overnight
jacqui248,
Dec 31, 11:15pm
ok thanks very much for the answer tmenz even if it aint what i want to hear LOL.
tmenz,
Dec 31, 11:26pm
These days the el-cheapo generators cost less than big batteries!
meathead_timaru,
Dec 31, 11:33pm
The difference being accounted from power factor of an AC induction motor such as that on the compressor. True vs apparent power. Domestic installations don't require Pf correction.
tmenz,
Dec 31, 11:46pm
I would expect the power factor of a small induction motor to be about 0.85~0.9. The above is around 0.5! I suspect the 0.7A figure is quoted as a maximum.
meathead_timaru,
Dec 31, 11:48pm
Our fridge Pf is about 0.65. But it is 20 years old. But you're right, factor margins everywhere add up quite quickly.
matarautrader,
Jan 1, 12:54am
Thats a great explanation that even I can understand.
busdriverman,
Jan 1, 3:08am
Some of those cheap generators don't have very good voltage control unless it is one of those inverter type generaters, if the fridge has any electronics in it, some do,it may cause problems. Also, IMHO generators running all day do not make nice camping neighbours, in these days of cheap solar panels.
jacqui248,
Jan 1, 12:48pm
well im hoping ill get this inverter real soon and try it out. and then i gonna get a new battery and we have a big old one here too. SOOO ill let you know how we get on!. wether we eating noodles last night due to rotten meat!.
tmenz,
Jan 1, 2:41pm
Yep, from a distance through a message board, with limited data and information, all we can do is make educated guesses and assumptions. Until it can be 'hands-on' with adequate time and measuring tools to make accurate observations, the estimates can only be 'ball-park' with large margin for error!
elect70,
Jan 1, 9:34pm
!2 Volt fridge or 3 waybetter thanconverting DC to ACto run ACfridge. Done a few for yachts& with 2batteries lasted3 days before needingcharge( had a littleauxmotor& alternator )
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