Xantrex Link 2000 Manuel d'utilisateur télécharger pdf (Page 25)

HIGH DISCHARGE RATES

& PEUKERT'S EQUATION

Peukert's Equation describes the effect of different discharge rates on battery

capacity. As the discharge rate increases the available battery capacity decreases. The

tables on pages 25, 26 and 27 have typical values of "n" for common batteries. Page 25

is a look-up table, pages 26 & 27 have "n" values for common batteries, and page 27 has

the formula for calculating "n" for other 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 amp hours

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 amp hours

of battery capacity consumed.

If battery Type 0 is selected, the initial Peukert exponent is set at 1.25. This

is an appropriate mid-range value for many common liquid cells. If any other battery

type is selected, the initial Peukert exponent is set at 1.11. This is an appropriate

mid-range value for many common gel and AGM cells. Please note that you may only

declare one battery type using function F02. This is because we strongly recommend

against mixing AGM, gel, and liquid electrolyte batteries in the same system. The

selected Peukert exponent is applied to both battery banks. Set the exponent to the

correct value for the bank which you use most often.

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

) is:

By doing two discharge tests and knowing I

& I

(discharge current in amps of

the two tests), and t

& t

(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.

= I

t where

log

- log t

log I

- log I

n =

1 2 ... 20 21 22 23 24 25 26 27 28 29 30 ... 42 43

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Xantrex Link 2000 Manuel d'utilisateur Page 25

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