How to Calculate Needed Batteries Size or Batteries Bank size in Ampere Hours Unit



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How to Calculate Needed Batteries Size or Batteries Bank size in Ampere-Hours Unit

https://www.nasirtech.com.au/how-to-calculate-needed-batteries-size-or-batteries-bank-size-in-ampere-hours-unit/

Introduction
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To calculate the batteries size for any application, you need to perform the following steps:
• Step 1: Some useful formula
• Step 2: Calculate the total load
• Step 3: Find out the right power inverter and batteries charger
• Step 4: Time requirement to run the system
• Step 5: Calculate the Ampere-Hours
• Step 6: Batteries Life-cycle and Discharge Consideration
• Step 7: Standard Batteries Ampere-Hours Rating
• Step 8: Determined the batteries Numbers
• Step 9: Summary with an electrical drawing
Step 1: Some useful formula
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The following formulas are required to find the Batteries bank size:
1.0 Power (P) = Voltage (V) * Current (I) Or P =V*I
2.0 I =P/V
3.0 Input Power (Pin) = Output Power (Pout) / Efficiency (η)%
or Pin = Pout / η
Step 2: Calculate the total load
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To find out the total load, you need to find out what kind of electrical equipment, you would like to run from this batteries bank. This can be determined by looking at the input electrical nameplate for each appliance or piece of equipment and adding up the total requirement.
1.0 Energy Saving Light Bulbs-Power Rating, P=24W
2.0 Cordless Phones-Power Rating
If V = 230V, A = 150mA or 0.15A
So, P= V*I
P=230V*0.15A
P=34.5W
3.0 Computer-Power Rating, P=230W
4.0 External Hard Drives-Power Rating, P=230W
5.0 Printer-Power Rating, P=230W 230W
Total= 748.5W or 750W (Approximately)
Step 3: Find out the right power inverter and batteries charger
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Batteries or Batteries Bank store energy in Direct Current or DC form. To convert Direct Current or DC into Alternative Current or AC, Power inverter requires. Batteries charger also requires charging the batteries. For this case, let consider, the batteries charger is integrated with power inverter. We know that every electrical device has some energy loss. To find out the energy loss, equipment manufacturer will provide the efficiency (η) in %. Most of Power inverter will have 80-85% efficiency.
Example:
Output Power (Pout) =750W
Efficiency (η) = 85% or 0.85
Input Power (Pin) = ?
Pin = 885W (Approximately)
Step 4: Time requirement to run the system
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Now, you need to make a decision “How long do you want your load to run?”. Let consider, the load need to run t=3 hours.
Step 5: Calculate the Ampere-Hours
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Before calculate the Ampere-Hours, we need to find out the Ampere or Current rating from our load.
Total Load Formula = 885W
Formula:
Current (I)= Power (P) / Voltage (V) Or I =P/V
Current for 12VDC
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I = 74A (Approx.)
Current for 24VDC
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I = 37A (Approx.)
The equation for the Ampere-Hours:
Ampere-Hours = Current (I) in Ampere (I) * Time (t) in Hours
Ampere-Hours Calculation
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Current Ampere-Hours for 12VDC
74 A for 24VDC, 74A * 12VDC or 888A.h

Current Ampere-Hours for 24VDC
37 A for 24VDC, 37A * 24VDC or 888A.h
Step 6: Batteries Lifecycle and Discharge Consideration
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To improve batteries lifetime, it is recommended that batteries should not be discharge completely. The maximum allowable discharge depends on the type of the batteries are used such as alkaline, carbon zinc, zinc-air and lead acid batteries. Also, some batteries cannot discharge 100% in fast discharge rating. The main reason of that is batteries chemical property.
Let consider, we will use such batteries which will allow maximum 50% discharge according to manufacturer recommendation.
Ampere-Hours Calculation according to manufacturer recommendation
Maximum Discharge Rating = 50% or 0.50
Ampere-Hours= 888A.h / 0.50 or 1760A.h
Step 7: Standard Batteries Ampere-Hours Rating
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Most of batteries manufacturer will provide batteries in A.h at a continuously current rating.
Most of the automation batteries are rated 70A.h at current of 3.5A. This mean that it will provide 3.5A current for 20hours, because 70A.h/3.5A = 20h
Step 8: Determined the batteries Numbers
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Let consider, we will use following type of batteries:
• 100A.h batteries at 5A current for 24VDC
• 50A.h batteries at 5A current for 12VDC

Batteries Number Calculation
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Require Ampere-Hours = 1760A.h
Require Batteries for 24VDC,
N=1760A.h/100A.h
N=17.6 or
N=18 (Approx.)

Require Batteries for 12VDC
N=1760A.h/50A.h
N=35.2 or
N=36 (Approx.)

Finally, we determined that 18 of 24VDC batteries or 36 of 12VDC batteries bank require to run 750W or 0.75kW at 3hours
continually.


Post time: Oct-19-2017
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