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.

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?

Say for example a 103AH Deep cycle Marine battery.

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.

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...

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.

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.

right, what'd I say?... thanks for the clarification :)

How about adding a wind power generator, especially for the crappy days? Does crappy weather generally come with wind?

Adding a wind power generator will be great. You may try this.

just to throw my shoe into the ring ...

103 @ 25% max. discharge /1.9 ah = more like 12 hours of continuous power. do you really need to run the pump 24/7? As many have pointed out (okay so I'm a lurker) the actual draw may be less than the rating indicates.

Also, when the sun shines not only will your batteries be charging but the draw will be covered by the panels. How much PV are putting into them?

@indyplumber/guercio: the windmaps for Ontario indicate a "poor" for windpower. Unless he's on a great lake or some'at.

not being an engineer means I'm big on "try it and see if it works..." so good luck!:thumbup: this summer I went from small 12 volt "trailer" deep cycle, to two 235 amp/hr 6 volts in series--1 250 watt panel in; to two 395 amp/hr 6 volts in series--2 250 watt panels in; to aha, this works!:D

How long will a 12v battery last with a .0228kW drain on it?
If I have say a 800cranking amp deep cycle battery?

12v Load = 1.9A
12v x 1.9A = 22.8W = P

22.8wh


1.Add up the hours that each Load will be on for to get the Total of Energy Consumed.
2.From that you can Calculate everything you need IE: Solar Panel / Battery / Regulator
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My Calculations

1 X 12V Pump @ 22.8W
on for (SEE CHART) hours per night
...................

-Watt/Hour Chart-
1 hour = 22.8Wh
2 hour = 45.6Wh
4 hour = 91.2Wh
8 hour = 182.4Wh


Total usage per night in Winter = 182.4Wh/d
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-Load and Battery -

Consumption = 182.4Wh over 8 hours
182.4 watt-hours divided by 12 volts = 15.2 amp hours taken from system in 1 night

Because we can only use half the energy in a lead acid battery without harming the battery,
the minimum battery size is 15.2 amps / .5 = 30.4Ah.

30% Discharge rule - the minimum battery size is 15.2 amps / .3 = 50.67Ah.
20% Discharge rule - the minimum battery size is 15.2 amps / .2 = 76Ah.

choose what calculation will be best for your battery !!
10% discharge is a non no.

I want my system to be reliable if we have four consecutive days of cloudy weather,
(using the 30% Discharge rule) 4 days of autonomy x 50.67Ah = 202.68Ah for the battery. = 210Ah + battery
(Required Battery Bank = 1 x 200 or 220 Ah True Deep Cycle

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-Charging Battery from Panel-
This installation is in a location that gets 4 hours of full sun per day.
Check the charts for this depending on the month in the Season.
To recharge the battery for one day of use we need 50.67 amps in 4 hours = 50.67 / 4 = 12.7amps from a 12 volt solar panel array.
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-Solar Panel -
Most load calculations include a discount factor for the inefficiency of recharging the battery.
20% is typical. 12.7 / 0.8 = 15.83A

A 2 x 140W solar array that has an Impp (amps maximum power point) of 7.7A = 15.4A would be suitable

------------------------------------------------------------------------------------------

-Charge Controller Rating in AMPS-
The 2 x 140W solar array has a short circuit amp rating (Isc) of 2 x 8.2A = 16.4A
16.4A x 1.25 = 20.5A
use a 20.5A or larger charge controller with this array to charge the battery.

Cheap example - 30A Unit
For best efficiency to charge use an MPPT Type.
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- estimated Cost of mentioned Materials -

Have seen 2 x 140w poly panel on Net for $340 inc delivery
Have seen 220Ah Varta Leisure Battery 12V 220Ah for around $300 inc delivery
20A Charge controller $80 - mppt prefered of course
Mounting Bracket for Panel = $20

Estimated Total = $640ish

Also required - Fuse box / switches / bits .. !!

Question ...If above calculations are based on a maximum of 8 hours use = 640
so 4 hours would mean 320 and 2 hours would = $160 for a 45.6W/h Load would all this calculate back nicely ?


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-Solar Panel specification-
STK-140P6-A ...... manufactured by 3E
Related power
140W
Open circuit voltage Voc(V)
23V
Short-circuit current Isc(A)
8.2A
Optimum operation voltage Vmp(V)
18.3V
Optimum operation current Imp(A)
7.7A

The above methods of calculation have all been taken from the Net over time !!
They seem to work, but if you think they are wrong then let me know.

Remember 12V Batteries should be fused and Stored in a safe manner

http://ecorenovator.org/forum/solar-...ally-need.html

:)

http://eaae-astronomy.org/blog/wp-co...ls20110618.jpg