Samlexpower PST-100S-12E Owner's Manual - Section 7 |
22 | SAMLEX AMERICA INC.
Intheexamplegivenabove,the10.7VLowBattery/DCInputAlarmwouldtriggerat
around80%dischargedstate(20%SoC)whentheC-RatedischargecurrentisC/5Amps.
However,forlowerC-RatedischargecurrentofC/10Ampsandlower,thebatterywillbe
almostcompletelydischargedwhenthealarmissounded.Hence,iftheC-Ratedischarge
currentislowerthanC/5Amps,thebatterymayhavecompletelydischargedbythetime
theLowDCInputAlarmissounded.
Low Dc input Voltage Shut-down in inverters:Asexplainedabove,ataround80%State
ofDischargeofthebatteryatC-RatedischargecurrentofaroundC/5Amps,theLow
DCInputVoltageAlarmissoundedataround10.7Vfora12Vbattery(ataround21.4V
for24Vbattery)towarntheusertodisconnectthebatterytopreventfurtherdraining
ofthebattery.Iftheloadisnotdisconnectedatthisstage,thebatterieswillbedrained
further to a lower voltage and to a completely discharged condition that is harmful for
the battery and for the inverter.
Inverters are normally provided with a protection to shut down the output of the
inverteriftheDCvoltageattheinputterminalsoftheinverterdropsbelowathreshold
ofaround10Vfora12Vbattery(20Vfor24Vbattery).ReferringtotheDischargeCurves
givenatfig7.1,theStateofDischargeforvariousC-Ratedischargecurrentsforbattery
voltageof10Visasfollows:(PleasenotethattheX-Axisofthecurvesshowsthe%of
StateofCharge.The%ofStateofDischargewillbe100%-%StateofCharge):
- 85%StateofDischarge(15%StateofCharge)atveryhighC-ratedischarge
currentofC/3Amps.
- 100%StateofDischarge(0%StateofCharge)athighC-Ratedischarge
currentofC/5Amps.
- 100%discharged(0%Stateofcharge)atlowerC-rateDischargecurrent
ofC/10Amps.
ItisseenthatatDCinputvoltageof10V,thebatteryiscompletelydischargedforC-rate
dischargecurrentofC/5andlower.
Inviewoftheabove,itmaybeseenthatafixedLow DC Input Voltage Alarm is not use-
ful.Temperatureofthebatteryfurthercomplicatesthesituation.Alltheaboveanalysis
isbasedonbatteryelectrolytetemperatureof78°f.Thebatterycapacityvarieswith
temperature. battery capacity is also a function of age and charging history. older bat-
terieshavelowercapacitybecauseofsheddingofactivematerials,sulfation,corrosion,
increasingnumberofcharge/dischargecyclesetc.Hence,theStateofDischargeofa
batteryunderloadcannotbeestimatedaccurately.However,theLowDCInputVoltage
AlarmandShutDownfunctionaredesignedtoprotectteinverterfromexcessivecur-
rent draw at the lower voltage.
Use of external Programmable Low Voltage Disconnects
Theaboveambiguitycanberemovedbyusinganexternal,programmableLowVoltage
Disconnectwheremoreexactvoltagethresholdcanbesettodisconnectthebattery
seCtIOn 7 |
General Information on Batteries for