Samlexpower PST-15S-12E Owner's manual - Section 7 |
20 | SAMLEX AMERICA INC.
SAMLEX AMERICA INC. | 21
seCtIOn 7 |
General Information on Batteries for
Powering Inverters
cablesarethickenoughtoallowanegligiblevoltagedropbetweenthebatteryand
theinverter).
Inverters are 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 10.5V for a 12V battery or 21V for 24V battery at C-Rate discharge current of C/5
Amps and electrolyte temp. of 80°F (by convention, battery data is normally presented
at 80°F).TheinverterisshutdowniftheterminalvoltageatC/5dischargecurrentfalls
furtherto10Vfor12Vbattery(20Vfor24Vbattery).
TheStateofDischargeofabatteryisestimatedbasedonthemeasuredterminalvoltage
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
temperatureof80°f.(PleasenotethattheX-Axisofthecurvesshowsthe%ofStateof
Charge.The%ofStateofDischargewillbe100%-%StateofCharge).
Low Dc input Voltage Alarm in inverters
Asstatedearlier,thebuzzeralarmistriggeredwhenthevoltageattheDCinputtermi-
nalsoftheinverterhasdroppedtoaround10.5Vfora12Vbattery(21Vfor24Vbattery)
atC-RatedischargecurrentofC/5Amps.Pleasenotethattheterminalvoltagerelative
toaparticularofStateDischargedecreaseswiththeriseinthevalueofthedischarge
current.forexample,terminalvoltagesforaStateofDischargeof80%(StateofCharge
of20%)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