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Old 04-29-11, 10:35 AM   #1
cdig
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Default Battery drain calculation?

I'm trying to figure out if I can circulate water in my horse waterer on a 12v deep cycle battery...

My numbers are:

12v pump that draws 1.9amps (12 x 1.9 = 22.8watts)
22.8w /1000 = .0228kW
.0228 x 24hours = .5472kWh ??


So given the above numbers, I'm hoping someone knows how to calculate just how long a 12v battery will last with a .0228kW drain on it? If I have say a 800cranking amp deep cycle battery?

Thanks,

C.

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Old 04-29-11, 10:42 AM   #2
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You need to know the Ah capacity of the battery to calculate how long it'll last. Do you have any info on your battery?
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Old 04-29-11, 01:10 PM   #3
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Say for example a 103AH Deep cycle Marine battery.
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Old 04-29-11, 01:11 PM   #4
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Motomaster Nautilus Deep Cycle Battery | Canadian Tire
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Old 04-29-11, 01:59 PM   #5
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Great. The calculation is pretty simple.

103Ah / 1.9A = 54 hours.

Of course, you don't want to drain a lead acid battery down that far because it'll reduce the number of cycles you get out of the battery. For optimal life, 50% is used for lead acid batteries. So, you really only have 51.5 Ah available to use, or 27 hrs.

If you were drawing more power you'd also have to take into effect the Peukert effect which basically says the faster you drain a battery, the less capacity it able to be used. However, the amperage you're pulling is so small compared to the battery size that it won't matter.
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Last edited by Daox; 04-29-11 at 02:04 PM..
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Old 04-29-11, 03:34 PM   #6
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ok, thanks. So if I hooked up 2 in series, that should in theory give me a couple days of continuous use? I'm going to have a pv panel recharging the battery but in cases where we get a couple days of crappy weather it may not recharge the battery much...
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Old 04-29-11, 04:48 PM   #7
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It's best to have 3 to 4 days worth of capacity to make your batteries last longer, in other words would you rather have 4 batteries last 10 years or 2 batteries last 3 years, because if you can keep the batteries in 70-80% full they should last 10-15 years as long as they don't run low on water.
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Old 05-01-11, 10:14 PM   #8
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Quote:
Originally Posted by cdig View Post
ok, thanks. So if I hooked up 2 in series, that should in theory give me a couple days of continuous use? I'm going to have a pv panel recharging the battery but in cases where we get a couple days of crappy weather it may not recharge the battery much...
If you hook up the batteries in series, you'll get 24 volts. However, if you hook up the positives together, and the negatives together (parallel), you stay at 12 volts but have more amperage available.
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Old 05-27-11, 02:26 PM   #9
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How about adding a wind power generator, especially for the crappy days? Does crappy weather generally come with wind?
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Old 05-03-11, 04:48 PM   #10
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right, what'd I say?... thanks for the clarification
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