Zivan FSSA15, Инструкция по установке и эксплуатации, Страница: 17 / 28

BATTERY DISCHARGER at constant current English
D01470-03 17
Battery discharge
Two methods exist to check the charging state of the battery:
1) The measuring method of the electrolyte density.
The electrolyte density is measured by means of an instrument called hydrometer.
This measurement have to be carry out with the maximum care and it has the drawback of depending on
the temperature.
In case of an electrolyte temperature equal to 30° you have:
density of about 1,26 kg/dm³ (30 °Bé): charged battery
density included between 1,26 kg/dm³ (30 °Bé) and 1,20 kg/dm³ (24 °Bé): battery partly
discharged
density less 1,14 kg/dm³ (18 °Bé): battery fully discharged
2) The measuring method of the voltage during the discharge.
The minimum voltage values of the single cell that can be reached during the discharge depend on the
discharging current in conformity with this correlation:
Vstop
I
Inom
= − ×
1,7385 0,0385 where Inom = nominal current =
C5
5h
I = discharging current
Thus discharging with a current intensity equal to 5 hours rating (i.e. I = Inom ) the voltage at which the
discharging must stop is:
Vstop = 1,7 Volt/cell
Operating directions
The ZIVAN battery discharger employs the measuring method of the voltage during the discharge.
Such method usually requests the discharging of the battery with constant current till the reachment of the
discharging limit voltage Vstop.
The property of keeping the battery discharged current constant can be obtained only from an electronic
device which changes its own resistance in conformity with the changing voltage. According to the
applied battery voltage and to the required discharging current, the discharger automatically selects some
different resistors and, with MOSFET technology at 20kHz, executes, through an adjustment of PWM
(Pulse Width Modulation), the change of duty cycle necessary to keep constant the current in conformity
with the change of battery voltage.
The high frequency electronic control provides smooth DC current draw from the battery, with no ripple.
By means of the timer with automatic shut-off it is possible to fix the discharging time. That allows to carry
out some partial discharges and in that way to increase the flexibility of the equipment.
Block Scheme
L
E
N
RECTIFIER
AND
FILTER
CONTROL
LOGIC
RS232
KEYBOARD
DISPLAY
PWM
M
VENTILATION
+
-
POWER
STAGE