Determine battery quantity

[pilotoo1]

Can someone show me how to calculate the number of batteries needed to power 500 watts of 120 volt AC lights for 8 hours with (x number of)12 volt DC batteries (going through an inverter) with 200 AH capacity each. Is more imformation needed? Can this be calculated? Not necessary to included % of ineffiencies of inverter, wire, connections, etc at this time. I just trying to get a nominal number at this time.

Thank you
Richard

 

[Skogsgurra]

calculate the number of batteries needed to power 500 watts of 120 volt AC lights for 8 hours with (x number of)12 volt DC batteries (going through an inverter) with 200 AH capacity each.

It is quite straightforward. Your load is 500 W. You will be running that for 8 hours. So you need 500*8 = 4 000 watt-hours [Wh].

Now, a 12 V 200 Ah battery contains 12*200 V*Ah = 2400 Wh (volts times amperes = watts, at least in DC).

How many batteries needed? You guessed it; more than 4000/2400, which seems to be 2. So, you need two such batteries.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[DanEE]

The only thing I would add to the above post is obtain and take a look at the AH rating discharge data sheets for the batteries you have in mind.

Battery discharge curves (obviously non linear) will show that the more current you pull from a individual battery, it will begin to fall short of the AH rating.. The advertised AH rating references a specific point off the discharge curve. Above or below that point the values will be different.

In the attachment below for the unity batteries that we frequently use on smaller systems, the current rating versus time charts are at the very bottom of the pdf file.

http://home.4x4wire.com/deddleman/

 

[pilotoo1]

Thank you for your answer. Is it different if the 2 batteries are wired in series vs. parallel? 2) 12 volts @ 12 volt output vs. 2) 12 volts @ 24 volts?

And are there Lithium or nickle-based 12 volt batteries available at 200 AH ratings? If so who? I'm looking for fast charge features of these type batteries.

 

[OperaHouse]

Inverters are only about 80% efficient. Add to that the AH of a battery decreases with higher load, Peukert effect. And it is not good to draw even deep cycle batteries down to nothing. I would use three batteries.

 

[rbulsara]

pilot001:

Think of batteries as pumps. When in series, the voltages (head or pressure) add up, the AH (capacity or gpm) remains the same. When in parallel voltage (head) remains the same, AH (capacity) add up.

So quantity and rating of batteries also depends on the inverter input voltage range and the how batteries would be configured. It is possible that you may end up with more capacity than required just to make up the right voltage.

 

[Skogsgurra]

Don't confuse the OP!

He said: " Not necessary to included % of ineffiencies of inverter, wire, connections, etc at this time. I just trying to get a nominal number at this time."

I tried to answer what he asked. Nothing more.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[itsmoked]

Skoggs; You know that doesn't work with a bunch of EEs.!!

If this is a cyclic load and you are going to have this occurring frequently then you need to NOT drain the batteries below 50% or the battery cycle lifetime will plunge.

The exotic batteries which you suggest will cost a small fortune and preclude using off-the-shelf equipment. I would estimate the cost of your system exceeding 10X any good lead acid (LA) solution.

You want fast recharge? Just select the newer LA system called AGM these charge very quickly and are of high performance.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[Skogsgurra]

My mistake, Smoked! Should've known..

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...