Rev 6.3.0 12.09.16
PL Reference Manual
15
6
6.4 SOC (State of Charge Display)
SOC (State Of Charge) should be read as a
percentage estimate of how full the battery is.
The estimate is based on the amp hour balance
counter. This counter keeps a running balance
of amp hours in vs amp hours out. The SOC
display shows this balance as a percentage of the
battery size. Note that all system currents must
be monitored by the PL and the battery capacity
(BCAP) must be entered by the installer for SOC
to be meaningful.
Over time, the amp hour balance counter
will drift out of line with the real battery
state of charge. To realign the counter the PL
automatically makes two corrections:
1. When the PL state changes from Absorb to
Float AND the charge duty cycle is less than
25%, SOC is reset to 100%.
2. SOC is capable of reading more than 100%,
however as soon as 1Ah of discharge is
recorded it will be set back to 100%, thus
discarding any surplus amp hours. These amp
hours were really put into the battery, but the
battery cannot be more than 100% full. The
difference is mostly the inherent loss in the
battery. The battery is never 100% efficient.
Note:
A long push on the SOC screen will reset
the unit to 100%.
The SOC figure should be treated with caution,
as there are several reasons that it may be
inaccurate:
•
The PL does not automatically have
knowledge of the whole system. It only
knows what you tell it. For SOC to work at
all, the PL must be measuring all charge (Ah
in) and discharge (Ah out). If the battery can
charge or discharge without the PL knowing,
SOC will not be meaningful.
•
Variations in charge efficiency mean SOC will
tend to be a little optimistic.
•
The effective capacity of the battery reduces
with age. BCAP should be reduced in older
batteries to adjust for this.
•
When you set up BCAP on installation, you
should choose your best guess of the batteries
actual capacity when used in the way you
intend to use it. For example, if you think the
battery will mostly be charged and discharged
at around the 100h rate (C/100) you should
set the capacity of you battery at the 100h
rate from the manufacturer’s literature. If
you expect the battery to be used at various
charge and discharge currents, try to estimate
an average. In many systems it is more
accurate to use the C/20 rate.
•
Battery self discharge and variations in
temperature will also cause some inaccuracy.
SOC (%) =
BCAP
Ah balance counter x 100
Ah balance counter=running balance of Ah IN vs Ah OUT
BCAP=battery capacity Ah input set upon installation
