12V fridge question

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Alrob

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okay so I went to the boat yesterday to discover that 110amp deep cycle battery 1 (new) was flat - question is - the shore power had been disconected for 60 hours the fridge was on at setting 4 ( 5 being max) and I had left the cd on - should the battery have flattened ???

battery 2 was fine as it was not switched on
oh and cabin was like a oven with the weather
 
What sort of fridge is it? Absorption or compressor? If the former, your battery went flat hours (days!) before you got back to the boat. Similarly compressor unless you have one of those super smart extremely low consumption ones - even then the odds are against it in this weather.
 
ah dont know the answer to that as the instruction are on the boat- all I can remember is that it is a norcold - boat is a 2005 model
 
A battery should never be drained below 50% of its rated power, and 60% is better. This means that from a 110amp battery you only have 40-50 available amps!
If you have an absorbtion type fridge thats stays on all the time it will be drawing around 9amps an hour, i.e. 4-5 hours and your battery is flat. If you have a compressor type fridge this will draw around 4/5 amps when the compressor is running. On average the compressor will run about half an hour every hour, so the draw will be around 3amps per hour. i.e. around 15 hours before its flat!

So the answer is yes after 60 hours its probably clapped out and may not be of any use anymore.

Barry
 
thanks for the info barry - that gives me food for thought.

makes me wonder though what would happen if I was moored for a day or 2 with no shore power ! ! !
 
[ QUOTE ]
If you have a compressor type fridge this will draw around 4/5 amps when the compressor is running. On average the compressor will run about half an hour every hour, so the draw will be around 3amps per hour.

[/ QUOTE ] Clearly we are in agreement that his battery will have expired very early on (and is probably terminally damaged) but there are compressor fridges now that consume very much less than this. Costly tho'
 
You need more battery capacity.
Rule of thumb is that you are unlikely to charge batteries much above 85% of capacity and it is wise not to discharge below about 50% of capacity. This means that you have roughly one third of capacity (in your case about 40A/Hrs)available for real use. Most modern 12volt fridges will probably consume this in around 24 hours elapsed time.
I have 440A/hrs of battery capacity (4 x 110) and this gives me around 150A/hrs of useable power which is enough to stay moored up for at least two days before needing to recharge. Even in ther ecent very hot weather this has coped admirably. Howver, if you want to be able to leave the fridge on for ,say 5 days, between charges then you would need at least 600A/hr capacity.
 
Most modern fridges will not completely flsatten your battery, they have an auto shutdown, when the voltage (under load) drops to 11.5 volts, which is a technically flat battery, but doesnt unless is done often damage the battery too much. I would be wondering whats going on, but of course if you also left on the CD, that would have done for the battery after the fridge shut down. You nay be able to save the battery, worth a try. Give iot a good charge and see how it goes.
 
no way a 110 battery can run a fridge for 60 hours, but as it is a deep cycle (leisure) battery it should not have been damaged. I thought that was what a deep cycle battery was for - deep cycling. Can any technos confirm that? Mine have run near flat several times without problem recharging. A starting battery would be a different matter.
 
I agree. While a single flattening a deep cycle battery may have a very slight effect on its life it certainly will not kill it, as many are claiming, unless it was about to die anyway.

In fact, and my experience is the same as the fact /forums/images/graemlins/smile.gif, even flattening a thin plated cranking battery that is in good condition does not "kill" it, but obviously an event to be avoided. I suspect most of us have flattened an otherwise healthy car battery at some time by leaving the lights on or some such - I doubt that many of us have found the battery destroyed through doing so though.

John
 
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