DC-AC Power Inverter Pure Sine Wave PST-1500 ... - DonRowe.com

SECTION 7 | General Information on Batteries forPowering Inverterscables are thick enough to allow a negligible voltage drop between the battery andthe inverter) .Inverters are provided with a buzzer alarm to warn that the loaded battery has beendeeply discharged to around 80% of the rated capacity. Normally, the buzzer alarm istriggered when the voltage at the DC input terminals of the inverter has dropped toaround 10.5V for a 12V battery or 21V for 24V battery at C-Rate discharge current ofC/5 Amps and electrolyte temp. of 80°F. The inverter is shut down if the terminal voltageat C/5 discharge current falls further to 10V for 12V battery (20V for 24V battery).The State of Discharge of a battery is estimated based on the measured terminal voltageof the battery. The terminal voltage of the battery is dependent upon the following:- Temperature of the battery electrolyte: Temperature of the electrolyte affects theelectrochemical reactions inside the battery and produces a Negative VoltageCoefficient – during charging / discharging, the terminal voltage drops with rise intemperature and rises with drop in temperature- The amount of discharging current or “C-Rate”: A battery has non linear internalresistance and hence, as the discharge current increases, the battery terminal voltagedecreases non-linearlyThe discharge curves in Fig. 7.1 (page 19) show the % State of Charge versus the terminalvoltage of a 12V battery under different charge /discharge currents, i.e. “C-Rates”and fixed temperature of 80°F. (Please note that the X-Axis of the curves shows the % ofState of Charge. The % of State of Discharge will be 100% - % State of Charge).Low DC Input Voltage Alarm in InvertersAs stated earlier, the buzzer alarm is triggered when the voltage at the DC input terminalsof the inverter has dropped to around 10.5V for a 12V battery (21V for 24V battery)at C-Rate discharge current of C/5 Amps. Please note that the terminal voltage relativeto a particular of State Discharge decreases with the rise in the value of the dischargecurrent. For example, terminal voltages for a State of Discharge of 80% (State of Chargeof 20%) for various discharge currents will be as follows (Refer to Fig. 7.1, page 19):Discharge Current:C-RateTerminal Voltage at 80% Stateof Discharge (20% SOC)Terminal Voltage When CompletelyDischarged (0% SOC)C/3 A 10.45V 09.50VC/5 A 10.90V 10.30VC/10 A 11.95V 11.00VC/20 A 11.85V 11.50VC/100 A 12.15V 11.75VSAMLEX AMERICA INC. | 21