# Sizing a 24V Deep-cycle Battery System for a specific application

#### Lei Reyes

Jul 2, 2014
60
Hi Everyone,

I have some devices that I need to connect to an OFF-GRID Power Source consisting of a;
(1) unit 500w Solar Panel
(1) unit 500w Wind Turbine
(1) unit hybrid charge controller
(1) unit pure sine wave inverter

All the devices must connect to a power strip that is connected to the inverter output.

Here are the Devices that I am going to use along with their DC-rating
*antenna - 8.5W max consumption, power supply is 24V 0.5A PoE adapter
*camera1 - 10W, 5V 2 A adapter
*sensor1 - 216mW, 12V 1A adapter
*sensor2 - 180mW, 12V 1A adapter
*RTU1 - 6W, 12V 2A Adapter
*IP Phone - 12W. 12V 2A Adapter
*Amplifier - 200W, connected directly to 220v output of the inverter

BUT I do not know how can I determine the following;
1. Ampere-Hour size of the (24v) deep-cycle battery to be used
2. how many deep cycle batteries I need to use to provide at least 72-hours of operation for my devices

I do not know how can I compute for these things given that;
*I only have the DC ratings of my devices, I do not know how long can a FULL-CHARGED (24V) Deep-cycle battery system provide for the Inverter to produce 220V for 72-Hours.

Thank you...

#### BannonMerkel

Apr 2, 2016
1
If you add up all of your watts for each device it looks like about 240w of load you will be consuming 24 hrs a day, assuming everything runs at full power.

Multiply this by 24 hours a day and that is the daily watt-hour demand of the system.

Now you can find what the neccesary Amp hour rating of the battery bank should be by dividing the watt hours by the voltage of the battery system then multiply by 3 for 3 days.

In reality, depending on the batteries you use, you may need to oversize the battery bank so the state of charge stays over 50% to prevent damage to the bank.

The charge controller, inverter and even battery bank have an efficiency to them so there are other losses to account for when sizing the system but each load device may not be operating at full load all the time.

It is very smart to design the batteries for 3 days of back up as the sun may not shine or the wind not blow for several days and is close to what I would design for, but you may want to use a tool like pvwatts.org to find what amount of energy yield you can expect in your area.

There is a lot more to look at when trying to figure this out but this may get you in the ball park of battery sizes.

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