Samlexpower PST-100S-12E Owner's Manual - Section 7 |
20 | SAMLEX AMERICA INC.
SAMLEX AMERICA INC. | 21
seCtIOn 7 |
General Information on Batteries for
Powering Inverters
theDCinputcablesarethickenoughtoallowanegligiblevoltagedropbetweenthe
batteryandtheinverter).
Inverters are normally provided with a buzzer alarm to warn that the loaded battery
has been deeply discharged to around 80% of the rated capacity. Normally, the buzzer
alarm is triggered when the voltage at the DC input terminals of the inverter has
dropped to around 10.7V for a 12V battery or 21.4V for 24V battery at C-Rate dis-
charge current of C/5 Amps and electrolyte temp. of 78°C (by convention, battery data
is normally presented at 78°C).TheinverterisshutdowniftheterminalvoltageatC/5
dischargecurrentfallsfurtherto10Vfor12Vbattery(20Vfor24Vbattery).
TheStateofDischargeofabatteryisnormallyestimatedbasedonthemeasuredtermi-
nal voltage of the battery. The terminal voltage of the battery is dependent upon the
following:
- temperature of the battery electrolyte: Temperature of the electrolyte affects the
electrochemicalreactionsinsidethebatteryandproducesaNegativeVoltage
Coefficient–duringcharging/discharging,theterminalvoltagedropswithrisein
temperature and rises with drop in temperature
- the amount of discharging current or “c-Rate”:Abatteryhasnonlinearinternal
resistanceandhence,asthedischargecurrentincreases,thebatteryterminalvoltage
decreases non-linearly
Thedischargecurvesatfig.7.1showthe%StateofChargeversustheterminalvoltage
ofa12Vbatteryunderdifferentcharge/dischargecurrents,i.e.“C-Rates”andfixed
temperatureof78°f.(Byconvention,batterydataisnormallypresentedat78°f).(Please
notethattheX-Axisofthecurvesshowsthe%ofStateofCharge.The%ofStateof
Dischargewillbe100%-%StateofCharge).
Low Dc input Voltage Alarm in inverters
Asstatedearlier,thebuzzeralarmistriggeredwhenthevoltageattheDCinput
terminalsoftheinverterhasdroppedtoaround10.7Vfora12Vbattery(21.4Vfor24V
battery)atC-RatedischargecurrentofC/5Amps.Pleasenotethattheterminalvoltage
relativetoaparticularofStateDischargedecreaseswiththeriseinthevalueofthe
dischargecurrent.forexample,terminalvoltagesforaStateofDischargeof80%(State
ofChargeof20%)forvariousdischargecurrentswillbeasfollows:
DischargeCurrent:
C-Rate
Terminal Voltage at 80% State
ofDischarge(20%SoC)
TerminalVoltageWhenCompletely
Discharged(0%SoC)
C/3A
10.45V
09.50V
C/5A
10.90V
10.30V
C/10A
11.95V
11.00V
C/20A
11.85V
11.50V
C/100A
12.15V
11.75V