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Battery amp hours  RSS feed

 
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I am back with another question about batteries. The batteries that the solar store recommended to me in their original quote for the backup system were the following:

12V/110AH/20HR deep cycle AGM-GEL combination made by Master Solar.

They recommended that I use two of these. I recognize the nomenclature: 12V = 12 volt battery; 110AH = 110 amp hours; 20HR = 20 hours?

If 20HR indeed is 20 hours, does this mean that the battery can run for a maximum of 20 hours at 110AH before it needs to be recharged?

If one battery is 110AH, does this mean that you can get 220AH if the two are connected?

I had originally asked for a quote from the solar outfit here to run my aquaponics system, powered by a 92 watt submersible AC water pump in continuous use (24 hours), completely with solar. But I had a major sticker shock when I saw the quote, which prompted me to go in the direction of a backup system charged off the grid electric system that I wrote about here in previous posts.

In the original quote, they said I need 4 of the batteries listed above connected to produce 24V to adequately run the 92-watt pump 24 hours continuously with 3 - 100-watt solar panels. I assumed at the time that I needed the 3 panels to keep the batteries adequately charged. However, now I am not so sure. The pump only uses 92-watts per hour. That is less than one 100-watt light bulb in continuous use.

However, my reason for writing is to understand amp hours. I found a website that guides you to determine your battery needs. Below are the calculations to run my pump.

Pump: 92 watts X 24 hours = 2208 watts
Independence: 3 days - 2208 X 3 = 6624 watts
Battery drain:  40% - 6624 ÷ 0.4 = 16,560 watts
Amps required: 16,560 ÷ 24V = 690AH

These calculations, if correct, indicate that I need 690AH? to run the pump continuously. However, the 4 batteries that they recommended are only 110AH each. Any way you slice it, I cannot get that battery configuration to add up to the 690AH that the calculations say that I will need.

Am I missing something? Originally, I had thought that the four batteries were overkill, but after doing the calculations above, it seems that they might be insufficient.
 
pollinator
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Location: Southern Arizona. Zone 8b
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{Edited I forgot to calculate for 24V}

20hr rate means that the 110AH is at the 20 hr rate, or 5.5Amps for 20 hours (5.5A x 20hr = 110 AmpHours)

Lead Acid batteries experience what is refered to as the Peukert Effect.  Basically the effect means that at higher current draw, less total amp hours are available.  So you might think you can draw 11 amps for 10 hours, but in reality you'll only get maybe 7-8 hours.

If you connect two batteries in parallel then yes you get 12V at 220Ah.  Now you can draw 11 amps for 20 hours.

if your 92 watt pump runs on AC, then you'll need an inverter.  At that power level the inverter will probably be 70% efficient, or looking at it the other way around will have 30% loss.  So to get 92 watts to the pump you'd have to draw about 131 watts from the batteries.  That works out to about 11 amps, which means two of those batteries in parallel will last about 20 hours.

Of course that is 20 hours after they are broken in and while they are still fairly new.  If these are used in a backup capacity, instead of daily, then you'll probably get less than 20 hours, my 'guess' is around 18 hours.

{update}
With 4 batteries your pump should last around 40-45 hours, you'll need 6 batteries to last approx 3 days (Peukert is helping you in this case).

As has been mentioned a few times switching to a DC powered pump would probably be cheaper in the long run.  You'll avoid the cost of the inverter AND the losses incurred.   With a DC powered pump it's quite possible that 4 batteries would be enough.

Actually, it might be even better to use a DC powered water pump, so you can keep your vegetables alive, and use a water spray, venturi, etc. to oxygenate the water and do away with the air pump.  This would probably require less power to operate.
 
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Location: Northern Germany (Zone 8a)
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EDIT: striking out errors

is there a miscalculation?

If the pump uses 92Watt and is AC them it s AMPs should be lower. If you have 110Volts, the A would be 92/110 = 0,84 A
Please check with the specs/manual of your pump.

You could research using 12V DC pump which would erase the need for inverter and the losses of it. It should be more economic to invest in 12V pump than into more batteries, more panels and inverter
 
Posts: 347
Location: Michigan
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The company might have added expected solar charging to the calculation and most skimp back to 1.5- 2 days.

Here in the cloudy north of michigan, 4-5 days is a common autonomy.

All this is example of natural systems efficiencies and huge un-noticed power flows that ooccur in them. They are amazing.

670ah or more at 24v! We run our homestead off grid completely without a gen set on 440ah 24v!

Its a good commercial for soil gardening or a pond, or a water tower or cistern on a hill where water is pumped during daylight and water can return through oxygenating contours at night and on cloudy days.

That would be many times more expensive but the infrastructure could be maintained for lifetimes, especially a normal pond.

A water pump could come on every so many minutes for as long as it takes to refresh the holding tanks.

Its always a battle going against the flow.

https://www.pinterest.de/pin/484207397421788294/
 
Peter VanDerWal
pollinator
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Tobias Ber wrote:is there a miscalculation?

If the pump uses 92Watt and is AC them it s AMPs should be lower. If you have 110Volts, the A would be 92/110 = 0,84 A
Please check with the specs/manual of your pump.

You could research using 12V DC pump which would erase the need for inverter and the losses of it. It should be more economic to invest in 12V pump than into more batteries, more panels and inverter



Tobias, I'm not sure who you were asking, but,

Watts = Amps x Volts.

If you reduce Volts then you have to INCREASE Amps to get the same power.

Roughly speaking, when going from 120V to 12V Amps increase by 10x, this of course ignores conversion losses.   Ignoring conversion losses is a great way of running out of battery capacity sooner than you expected.
 
Tobias Ber
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Ok, sorry.... my brain produced an error message
 
Posts: 242
Location: Abkhazia · 400m elevation · temperate climate
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Hm.. maybe you can store the energy otherwise?
With two tanks for clean water – one low and one high, the pump would use the solar power directly to move the water up, without any batteries.
How much flow do you need?
 
Peter VanDerWal
pollinator
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Sebastian Köln wrote:Hm.. maybe you can store the energy otherwise?
With two tanks for clean water – one low and one high, the pump would use the solar power directly to move the water up, without any batteries.
How much flow do you need?



I think the general rule of thumb is to pump a quantity of water equal to your fish tank every hour.  So for one day backup, your storage tank would have to be 24 times as big as your fish tank.
 
Angela Aragon
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You are right, Peter. The proposed double-tank system, as described, would not be practical. However, I want to say that I appreciate the suggestion and all of the other responses to my questions that I have received. I am trying to educate myself and you guys have been a big help!
 
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Definitely look for a dc pump. The saving on inverters batteries and pv panels will easily justify a new pump. I dont know how much water you need to pump but it sounds like you dont have to pump to any height, so a cheap DC RV pump (ideally two for resilence) will cost you well under $100
 
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