Table of Contents
Advertisement
4
SETUP
4.1
Background information
4.1.1
Charge Efficiency Factor (CEF)
During battery charging, not all of the energy transferred into the battery
is available when the battery is being discharged. The charge efficiency
factor (CEF) of a brand new battery is approximately 90 %. This means
that 10 Ah must be transferred to the battery to get 9 Ah actually stored in
the battery. The CEF of a battery will decrease as the battery ages.
Peukert's exponent
4.1.2
As mentioned in chapter 1.4, the Peukert efficiency describes how, when
you discharge a battery faster than the 20 h rating, its Ah capacity
decreases. The amount of battery capacity reduction is called the
„Peukert exponent‟ and can be adjusted from 1.00 to 1.50. The higher the
Peukert exponent the faster the battery size shrinks with increasing
discharge rate. An ideal (theoretical) battery has a Peukert exponent of
1.00 and has a fixed capacity; regardless of the size of the discharge
current. Of course such batteries do not exist, and a setting of 1.00 in the
VBC-HV is only implemented to bypass Peukert compensation. The
default setting for the Peukert exponent is 1.25, and is an acceptable
average value for most types of lead acid battery. However for precise
battery monitoring, entering the right Peukert exponent is essential. If the
Peukert exponent is not provided with your battery, you can calculate it
by using other specifications which should be provided with your battery.
The Peukert equation is stated below:
n
where the Peukert exponent, n =
Cp
I
t
The battery specifications needed for calculation of the Peukert exponent,
are the rated battery capacity (usually the 20 h discharge rate
example a 5 h discharge rate
define the Peukert exponent using these two specifications.
1
Please note that the rated battery capacity can also be defined as the 10 h or even 5 h discharge rate.
2
The 5 h discharge rate in this example is just arbitrary. Make sure that besides the C20 rating (low discharge current) you
choose a second rating with a substantially higher discharge current.
8
log
t
log
I
1
2
. See below for an example of how to
log
t
2
1
log
I
2
1
) and for
Advertisement
Table of Contents
