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bobrok
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# Posted: 31 Aug 2014 16:38
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My son and his gf will occasionally use our cabin for short duration visits, perhaps 3-4 days. I have barrel stored water for showers, etc and use a shurflo 12 vdc demand pump. I don't keep my deep cycle battery at the cabin but bring it home to keep on charge.
What would be a minimum - type battery I can buy for them so that they can bring their own power supply when they come?
As an aside, my son's gf sometimes will come up alone and I'm hoping there is a lighter weight battery that would serve the purpose w/o having to lug up an auto - type battery.
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Steve961
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# Posted: 31 Aug 2014 21:40
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Is the pump the only thing that needs power, or do you also have lights, TV, etc.? My cabin has that same pump, but I also have several LED lights, a small TV, a fan, and also end up recharging cell phones and such.
If the pump was the only load, you might be able to get away with a 50 AH battery. At my cabin, and with my loads, I would want at least a 100 AH battery to go 3-4 days. I also have an AGM battery that can be discharged much lower than your typical lead-acid without fear of damage.
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bobrok
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# Posted: 1 Sep 2014 12:29 - Edited by: bobrok
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Yes, this is a dedicated battery for the pump only. I am not near my pump now but do you know what the amperage draw is? Is 7 amps correct?
There's conversion calculators to figure out cold cranking amps to amp hours.
I'm trying to see if there is a lighter weight and smaller battery they could use.
Thanks
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Steve961
Member
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# Posted: 1 Sep 2014 15:06
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Your pump should be 7 amps. With that, it's easy to figure out how big a battery you need.
From the standpoint of drawing from a flooded lead acid (FLA) battery, the rule of thumb is 1/8 capacity. So, you would want a minimum of a 56 (8*7) amp hour (AH) battery.
Looking at usage, if you planned to run the pump a total of 5 hours during your stay, you would use 35 AH (5*7) of power. If you then decided on a depth of discharge (DOD) of 50% for your battery, you would then need a 70 AH battery.
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bobrok
Member
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# Posted: 1 Sep 2014 22:05 - Edited by: bobrok
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Thanks for the help, Steve961. I ended up buying a standard deep cycle marine battery, 550 cca, 140 reserve cap. A 30% off on-line coupon also helped in my decision making. I guess a small, lightweight, long lasting, deep cycle battery is kind of an oxymoron anyways.
Son's gf will just have to learn how to lift weights. 
When the day comes to replace my ageing solar setup in the cabin itself I hope to incorporate the water pump into that system.
bob
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