Samlexpower PST-1000-12 Owner's manual - Section 7 |
26 | SAMLEX AMERICA INC.
ThefirststepistoestimatethetotalACwatts(W)ofload(s)andforhowlongthe
load(s)willoperateinhours(H).TheACwattsarenormallyindicatedintheelectrical
nameplateforeachapplianceorequipment.IncaseACwatts(W)arenotindicated,for-
mula1givenabovemaybeusedtocalculatetheACwatts.Thenextstepistoestimate
theDCcurrentinAmperes(A)fromtheACwattsasperformula2above.Anexample
ofthiscalculationfora12Vinverterisgivenbelow:
Let us say that the total Ac Watts delivered by the 12V inverter = 1000W.
Then,usingformula2above,theDCcurrenttobedeliveredbythe12Vbatteries
=1000W÷10=100Amperes.
next, the energy required by the load in Ampere Hours (Ah) is determined.
forexample,iftheloadistooperatefor3hoursthenasperformula3above,the
energytobedeliveredbythe12Vbatteries=100Amperes×3Hours=300Ampere
Hours(Ah).
now, the capacity of the batteries is determined based on the run time and
the usable capacity.
fromTable7.3“BatteryCapacityversusRateofDischarge”,theusablecapacityat
3Hourdischargerateis60%.Hence,theactualcapacityofthe12Vbatteriesto
deliver300Ahwillbeequalto:300Ah÷0.6=500Ah.
And finally, the actual desired rated capacity of the batteries is determined based on
thefactthatnormallyonly80%ofthecapacitywillbeavailablewithrespecttothe
rated capacity due to non availability of ideal and optimum operating and charging
conditions.Sothefinalrequirementswillbeequalto:500Ah÷0.8=625Ah(notethat
theactualenergyrequiredbytheloadwas300Ah).
It will be seen from the above that the final rated capacity of the batteries is almost
2timestheenergyrequiredbytheloadinAh.Thus, as a Rule of Thumb, the Ah
capacity of the batteries should be twice the energy required by the load in Ah.
fortheaboveexample,the12Vbatteriesmaybeselectedasfollows:
- Use6Group27/31,12V,105Ahbatteriesinparalleltomakeup630Ah,or
- Use3Group8D,12V,225Ahbatteriesinparalleltomakeup675Ah.
seCtIOn 7 |
General Information on Batteries for