Samlexpower PST-1500-12 Owner's Manual - Section 7 |
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7.8 REDUCTION IN USABLE CAPACITY AT HIGHER DISCHARGE RATES –
TYPICAL IN INVERTER APPLICATION
As stated above, the rated capacity of the battery in Ah is normally applicable at a dis-
charge rate of 20 Hours. As the discharge rate is increased as in cases where the inverters
aredrivinghighercapacityloads,theusablecapacityreducesdueto“PeukertEffect”.
ThisrelationshipisnotlinearbutismoreorlessaccordingtotheTable7.3.
TABLE 7.3 BATTERY CAPACITY VERSUS RATE OF DISCHARGE – C-RATE
C-Rate Discharge Current
Usable Capacity (%)
C/20
100%
C/10
87%
C/8
83%
C/6
75%
C/5
70%
C/3
60%
C/2
50%
1C
40%
Table7.3showsthata100Ahcapacitybatterywilldeliver100%(i.e.full100Ah)capacity
if it is slowly discharged over 20 Hours at the rate of 5 Amperes (50W output for a 12V
inverter and 100W output for a 24V inverter). However, if it is discharged at a rate of 50
Amperes (500W output for a 12V inverter and 1000W output for a 24V inverter) then
theoretically,itshouldprovide100Ah÷50=2Hours.However,Table7.3showsthatfor2
Hours discharge rate, the capacity is reduced to 50% i.e. 50 Ah. Therefore, at 50 Ampere
discharge rate (500W output for a 12V inverter and 1000W output for a 24V inverter) the
batterywillactuallylastfor50Ah÷50Amperes=1Hour.
7.9 STATE OF CHARGE (SOC) OF A BATTERY – BASED ON
“STANDING VOLTAGE”
The “Standing Voltage” of a battery under open circuit conditions (no load connected
toit)canapproximatelyindicatetheStateofCharge(SOC)ofthebattery.The“Stand-
ing Voltage” is measured after disconnecting any charging device(s) and the battery
load(s)andlettingthebattery“stand”idlefor3to8hoursbeforethevoltagemeasure-
mentistaken.Table7.4showstheStateofChargeversusStandingVoltageforatypical
12V/24Vbatterysystemat80°F(26.7ºC).
Section 7 |
General information on Lead Acid