est battery capacity calc

7/23/2019 Est Battery Capacity Calc

1/12

How to calculate how much batterycapacity (SLA Battery) you need.

Example:- Equipment draw 1.2A and we need to run for 12

hours

Step 1

Determine Capacity needed :- Capacity= 1.2 amp x 12 hrs = 28.8 A


2/12

How to etimate how much batterycapacity (SLA Battery) you need.

Step !:- Cycle li"eConideration:-

!o extend the cycle of lead acid "attery# we

shouldn$t run the "attery past 8%& of its capacity.

!hus#

Capacity = C'%.8

= 28.8 ' %.8= () A


3/12

How to etimate how much batterycapacity (SLA Battery) you need.

Step #:- $ate o" Dichar%econideration:-

*ome "attery chemistries +i,e much lesser fewer ampere

hours if we dischar+e them at a hi+her rate. E+:-

f a *A "attery rated at 1%%A# 2% hrs dischar+e rate

1/ f it is dischar+ed at 0A for 2% hours# the "attery will a"leto deli,er the rated capacity of the "attery# i.e 1%%A

2/ owe,er# if it is dischar+ed at 1%% A # the "attery will "edepleted within half an hour instead of the calculated 1hour . !his is called the euert E3ect.


4/12

&eu'ert law#presented "y the 4erman scientist 5ilhelm euertin 1867# expresses the capacityof a "attery in termsof the rate at which it is dischar+ed. As the rateincreases# the "atterys a,aila"le capacity decreases

euerts law is as follows:

Cp = 9tCp = is the capacity accordin+ to euert# at aone-ampere. dischar+e rate# expressed in A = the dischar+e current# expressed in

Amperes#a. = the euert constant#t = the time of dischar+e# expressed in hours# h.
https://en.wikipedia.org/w/index.php?title=Wilhelm_Peukert&action=edit&redlink=1https://en.wikipedia.org/w/index.php?title=Wilhelm_Peukert&action=edit&redlink=1https://en.wikipedia.org/wiki/Battery_(electricity)https://en.wikipedia.org/wiki/Battery_(electricity)https://en.wikipedia.org/w/index.php?title=Wilhelm_Peukert&action=edit&redlink=1https://en.wikipedia.org/w/index.php?title=Wilhelm_Peukert&action=edit&redlink=1


5/12

Examples:-

* 1 At 0A 1%% A 2% rs rate/

!=1%%'0;1.(/

= 12.( hrs

*. ! At 10.8A 76A 0 rs rate/

!= 76'10.8;1.(/

= 2.18 hrs


6/12

REVISED PEUKERTs LAW

The capacity at a one-ampere discharge rate is not usually given for practical cells. As such,

it can be useful to reformulate the law to a known capacity and discharge rate:

where:

is the rated discharge time (in hours,

is the rated capacity at that discharge rate (in ampere-hours,

is the actual discharge current (in amperes,

is the !eukert constant (dimensionless,

is the actual time to discharge the battery (in hours.
https://en.wikipedia.org/wiki/Ampere-hourhttps://en.wikipedia.org/wiki/Dimensionless_numberhttps://en.wikipedia.org/wiki/Dimensionless_numberhttps://en.wikipedia.org/wiki/Ampere-hour


7/12

Examples:-

* 1 At 0A 1%% A 2% rs rate/

!=2%1%%'0 x 2%/;1.(

= 2% hrs

*. ! At 10.8A 76A 0 rs rate/

!= 076'10.8 x 0/;1.(

= 0 hrs


8/12

&eu'ert Law Limitation

euert$s law is a ,alua"le tool for estimation. owe,er# ithas limitations. Amon+ them are

est battery capacity calc

Documents