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HIGH DISCHARGE RATES
& PEUKERT'S EQUATION
Peukert's Equation describes the effect of different discharge rates on battery ca-
pacity. As the discharge rate increases the available battery capacity decreases. The
tables and examples on the following pages illustrate this effect and how to use the table
to estimate the exponent "n". The tables on pages 26 & 27 have typical values of "n" for
common batteries.
The LINK 2000 uses Peukert's equation only for calculating the Time Remaining
of operation function. The Amp hours display is always the actual number of A hrs
consumed. This means that if you rapidly discharge a battery, your time remaining
number may show zero hours remaining before you see the total number of A hrs of
battery capacity consumed.
Making two discharge tests, one at a high discharge rate and one at a low rate, that
bracket your normal range of operation, allows you to calculate an "n" that will describe
this varying effect. The LINK 2000 uses a default value of "n" equal to 1.25 which is
typical for many batteries.
At some low to moderate discharge rate, typically a battery's 20 hour rate, the
logarithmic effect of Peukert's Equation is greatly reduced. The effect of discharge rates
smaller than this is nearly linear. Battery manufacturer specifications of battery capacity
in Amp-hours is typically given at the 20 hour rate. From this description, if a battery is
discharged at this rate for the period of time called out, you will be able to remove the
rated capacity.
The equation for Peukert's Capacity (C
p
) is:
By doing two discharge tests and knowing I
1
& I
2
(discharge current in Amps of the
two tests), and t
1
& t
2
(time in hours for the two tests) you can calculate n (the Peukert
exponent). You will need a calculator that has a Log function to solve the equation above.
You may also use the 20 hour discharge rate and the number of reserve minutes as the two
discharges to solve Peukert's equation. See example on page 27. After you solve for your
Peukert's exponent you may enter it using Function F08.
C
p
= I
n
t where
log t
2
- log t
1
log I
1
- log I
2
n =
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