This calculator is designed to calculate AC loads to DC battery banks +/- a battery. To compute DC loads to DC battery banks, click here.
Instant watt usage
-- watts amps x volts
Hourly Amp Hours Used @ 12v
Daily Amp Hours Used @ 12v
-- ah 24 Hours
Weekly Amp Hours Used @12v
-- ah 7 days
Monthly Amp Hours Used @12v
-- ah 30 days
AC to DC conversion is not perfectly efficient. To be safer, use the 80% (.8) efficient derate factor.
This calculator computes the number of batteries needed for any application +/- a battery. System is set to +20% (ah X 1.2) to account for wire resistance, resulting voltage loss, heat, and other DC system inefficiencies.
For Critical Applications battery sizing should be a starting point. Unusual circumstances call for an additional 100-500+ ah battery bank.
The computation does not account for losses of up to half ampacity for colder temperatures OR increased self discharge in warmer climates and on older batteries.
System does not account for amperages outside battery possible limits.
As a battery chemically transforms from fully charged to discharged, it’s voltage drops from 13.5 – 10.5 volts for a 12 volt battery. As the voltage drops this affects the amount of amps required to drive a load. (Watts law: amps x volts = watts)
13.5 volts x 10.00 amps = 135 watts
10.5 volts x 12.86 amps = 135 watts
As such, this calculator is for sizing purposes only. All systems should be thoroughly tested as they are installed to insure that the battery bank is appropriate for the load on that site.
AGM Batteries are not harmed by high amperage charge and discharge so long as the input voltage is carefully regulated.
Charge 12 volt batteries at 13.2 – 14.4 volts
Charge 6 volt batteries at 6.6 – 7.2 volts
Avoid over charging and remove from charger immediately (or divert to other load – PV, renewable). Over charged batteries will have a unnaturally short lifespan. AGM batteries are not affected by higher current charging as GEL and Flooded batteries can be.