Samlexpower PST-15S-12E Owner's manual - Section 7 |
24 | SAMLEX AMERICA INC.
Inverters are normally provided with a protection to shut down the output of the inverter
if the DC voltage at the input terminals of the inverter drops below a threshold of around
10V for a 12V battery (20V for 24V battery). Referring to the Discharge Curves given in
fig 7.1, the State of Discharge for various C-Rate discharge currents for battery voltage of
10V / 20V is as follows: (Please note that the X-Axis of the curves shows the % of State of
Charge. The % State od Discharge has to be converted to the % State of Charge using the
formula: % State of Charge = 100% - % State of Discharge):
- 85% State of Discharge (15% State of Charge) at very high C-rate discharge
current of C/3 Amps.
- 100% State of Discharge (0 % State of Charge) at high C-Rate discharge
current of C/5 Amps.
- 100% discharged (0% State of charge) at lower C-rate Discharge current of C/10 Amps.
It is seen that at DC input voltage of 10V / 20V, the battery is completely discharged for
C-rate discharge current of C/5 and lower.
In view of the above, it may be seen that a fixed Low DC Input Voltage Alarm is not useful.
Temperature of the battery further complicates the situation. All the above analysis is based
on battery electrolyte temperature of 80°f. The battery capacity varies with temperature.
battery capacity is also a function of age and charging history. older batteries have lower
capacity because of shedding of active materials, sulfation, corrosion, increasing number of
charge / discharge cycles etc. Hence, the State of Discharge of a battery under load cannot
be estimated accurately. However, the low DC input voltage alarm and shut-down functions
are designed to protect the inverter from excessive current drawn at the lower voltage.
7.13 USe oF eXteRnAL PRoGRAMMABLe LoW VoLtAGe DiSconnectS
The above ambiguity can be removed by using an external, programmable Low Voltage
Disconnect where more exact voltage threshold can be set to disconnect the battery
based on the actual application requirements. Please consider using the following
Programmable Low Battery Cut-off / “Battery Guard” Models manufactured by Samlex
America, Inc. www.samlexamerica.com
- BG-40 (40A) – for up to 400W, 12V inverter or 800W, 24V inverter
- BG-60 (60A) - for up to 600W, 12V inverter or 1200W, 24V inverter
- BG-200 (200A) - for up to 2000W, 12V inverter or 4000W, 24V inverter
seCtIOn 7 |
General Information on lead Acid