Samlexpower PST-100S-12E Owner's Manual - Section 7 |
18 | SAMLEX AMERICA INC.
seCtIOn 7 |
General Information on Batteries for
Powering Inverters
asthe“C-Rate”.Ifthebatterydeliversaveryhighdischargecurrent,thebatterywillbe
dischargedtothe“EndPointVoltage”inashorterperiodoftime.ontheotherhand,
ifthebatterydeliversalowerdischargecurrent,thebatterywillbedischargedtothe
“End Point Voltage” after a longer period of time. Mathematically:
eQUAtion 1:
Dischargecurrent“C-Rate”=Capacity“C”inAh÷DischargeTime“T”
Table7.2belowgivessomeexamplesofC-Ratespecificationsandapplications:
tABLe 7.2: DiScHARGe cURRent RAteS - “c-RAteS”
Hoursofdischargetime
“T” till the “End Point
Voltage”
C-RateDischargeCurrentinAmps
ExampleofC-Rate
DischargeCurrentsfor
100Ahbattery
fraction
Decimal
Subscript
0.5Hrs.
2C
2C
2C
200A
1Hrs.
1C
1C
1C
100A
5Hrs.
C/5
0.2C
C5
20A
8Hrs.
(UPSapplication)
C/8
0.125C
C8
12.5A
10Hrs.
(Telecomapplication)
C/10
0.1C
C10
10A
20Hrs.
(Automotiveapplication)
C/20
0.05C
C20
5A
100Hrs.
C/100
0.01C
C100
1A
note: Whenabatteryisdischargedoverashortertime,itsspecified“C-Rate”dischargecurrent
willbehigher.forexample,the“C-Rate”dischargecurrentat5Hourdischargeperiodi.e.0.2C
/C5/C/5Ampswillbe4timeshigherthanthe“C-Rate”dischargecurrentat20Hourdischarge
periodi.e.0.05C/C20/C/20Amps.
charging / Discharging curves
fig.7.1(page19)showsthecharginganddischargingcharacteristicsofatypical,6cell,
12V,LeadAcidbatteryatelectrolytetemperatureof80°f(byconvention,batterydata
isnormallypresentedat80°f).Thecurvesshowthe%StateofCharge(X-axis)versus
terminalvoltage(Y-axis)duringcharginganddischargingatdifferentC-Rates.for24V
battery,multiplyvoltageonY-axisby2for48Vbattery,multiplyvoltageonY-axisby4
(Please note that X-axis shows % State of charge. State of Discharge will be = 100% -
% State of Charge).Thesecurveswillbereferredtoinsubsequentexplanations.
Reduction in Usable capacity at Higher Discharge Rates –
typical in inverter Application
Asstatedabove,theratedcapacityofthebatteryinAHisnormallyapplicableatadis-
chargerateof20Hours.Asthedischargerateisincreasedasincaseswheretheinverters
aredrivinghighercapacityloads,theusablecapacityreducesdueto“PeukertEffect”.
ThisrelationshipisnotlinearbutismoreorlessaccordingtotheTable7.3(page19).