Electrical, Solar & HVAC

Array sizing, battery banks, charge controllers, inverters and generators.

• Generator Size Calculator Size a generator from running watts and starting surge, with the fuel it will burn per hour.
• Inverter Size Calculator Size an inverter from your running load and the surge of the largest motor, with the DC current it will draw.
• Off-Grid Battery Bank Calculator Battery bank size for an off-grid system — usable capacity, days of autonomy, depth of discharge and temperature derating.
• Solar Charge Controller Calculator Size an MPPT or PWM charge controller — output current, safety margin, and the maximum array the controller can take.
• Solar Panel Calculator How much solar you need — array size in kW, how many panels, and what it will generate over a year.
• Solar String Sizing Calculator How many panels can go in series — with the cold-weather voltage rise that decides the real limit.

Ohm’s law, power, energy, running costs and three-phase supplies.

• Electricity Cost Calculator What an appliance costs to run — per day, month and year — from its wattage, hours of use and your unit rate.
• Ohm's Law Calculator Enter any two of voltage, current, resistance and power, and get the other two — with the formula used shown.
• Voltage Drop Calculator Voltage lost along a cable run — from conductor area, length and current, for copper or aluminium.

Capacity, runtime and charge time for battery banks and UPS systems.

• Battery Charge Time Calculator How long a battery takes to charge from a given state of charge, at a given charger current.
• Battery Runtime Calculator How long a battery will run a load, accounting for usable depth of discharge and inverter efficiency.
• Watt-Hours to Amp-Hours Calculator Convert between watt-hours and amp-hours at a given battery voltage — the conversion every battery spec sheet assumes you can do.

Resistors, capacitors, inductors, dividers and LED current limiting.

• LED Resistor Calculator The series resistor an LED needs — value, nearest standard size, power rating and what the resistor wastes.
• Series & Parallel Calculator Combine resistors, capacitors or inductors in series or parallel — enter any number of values and get the equivalent.
• Voltage Divider Calculator Output voltage of a two-resistor divider, with the current it draws and a warning when the load will disturb it.