Amps, Volts and Watts Explained for Canadian Electrical Systems

Amps, volts and watts are printed on batteries, chargers, inverters, solar equipment, appliances and power stations. Although the values often appear on the same label, each one answers a different question.

Volts describe electrical potential, amps describe current and watts describe power. Understanding how these measurements work together helps you select compatible equipment, size a battery bank, estimate runtime and avoid overloaded wiring.

What Is the Difference Between Amps, Volts and Watts?

Volts

Voltage provides the electrical potential that can move current through a completed circuit. It is often compared with pressure in a water line.

A battery may show voltage while supplying no current because no appliance is connected. Current begins to flow when a suitable load completes the circuit.

Common voltage levels include:

• 5V for USB equipment
• 12V or 12.8V for RVs, trailers, boats and small off-grid systems
• 24V or 36V for trolling motors and larger DC installations
• 36V, 48V or 72V for golf carts and utility vehicles
• 48V or 51.2V for solar and backup storage
• 120V AC for standard household receptacles
• 120/240V split-phase service for many Canadian homes

Nominal voltage does not remain perfectly constant. Battery voltage changes with chemistry, state of charge, temperature and load.

Amps

Amps measure the flow of electrical charge. The connected equipment normally determines the amount of current it draws.

A charger or power supply rated for 30A does not automatically push 30A through every connected device. Its rating normally describes the maximum current it can provide under specified conditions.

Current affects:

• BMS and battery output limits
• Cable cross-section
• Fuse and breaker selection
• Connector and busbar ratings
• Voltage drop
• Heat at loose or corroded connections
• Charging time

Cold weather can make cables less flexible and reduce battery performance, so Canadian RV, marine and off-grid installations should be planned with appropriate cable routing and temperature-rated equipment.

Watts

Watts measure the rate at which electrical energy is transferred or used. A 1,000W heater consumes energy ten times faster than a 100W device while each operates at its rated power.

Watt ratings commonly appear on appliances, inverters, generators, solar panels, chargers and motors.

Volts, Amps and Watts Formula

• Watts = Volts × Amps
• Amps = Watts ÷ Volts
• Volts = Watts ÷ Amps

Calculating Watts

• 12V × 10A = 120W
• 24V × 10A = 240W
• 120V × 5A = 600W

A nominal 12.8V battery with a 100A continuous discharge rating has a simplified theoretical output of:

12.8V × 100A = 1,280W

Calculating Amps

A 1,200W appliance connected to 120V draws approximately:

1,200W ÷ 120V = 10A

If the appliance is powered from a 12V battery through an inverter, ideal battery current is:

1,200W ÷ 12V = 100A

At 90% inverter efficiency:

1,200W ÷ 12V ÷ 0.90 = approximately 111A

Calculating Volts

A 600W DC load drawing 25A operates at:

600W ÷ 25A = 24V

Use the calculation for analysis, but follow the equipment manufacturer’s rated operating voltage for the actual installation.

Same Power at Different Voltages

A 48V system requires approximately one-quarter of the current of a 12V system when supplying the same power.

This is one reason higher-voltage battery banks are used for larger inverters. A 3,000W load requires roughly 250A at 12V, 125A at 24V or 62.5A at 48V before conversion losses.

Cable Heating and Voltage Drop

Resistive loss follows:

Power Loss = Current² × Resistance

Doubling the current creates four times the resistive heating when cable resistance stays the same.

Higher-current systems generally need:

• Thicker cables
• Shorter cable runs
• Higher-rated connectors
• Appropriate busbars
• Proper overcurrent protection
• Clean, tight connections

Using Volts, Amps and Watts With Batteries

Voltage Compatibility

The inverter, charger and connected DC equipment must all be compatible with the battery-system voltage.

Charging Current

A 20A charger would theoretically restore 100Ah in five hours:

100Ah ÷ 20A = 5 hours

Real charging usually takes longer because current may taper, the cells may require balancing and the charger introduces losses.

For lithium batteries used in Canadian winters, also check the permitted charging temperature. Many LiFePO4 batteries restrict charging close to or below 0°C unless low-temperature protection or heating is provided.

Continuous and Peak Current

Continuous current is the amount the battery can supply for normal operation. Peak current is available only for a short event such as starting a motor or accelerating a golf cart.

Inverter Battery Current

Estimate inverter current with:

Battery Amps = Load Watts ÷ Battery Voltage ÷ Efficiency

For a 1,500W load at 90% efficiency:

• 12V system: approximately 139A
• 24V system: approximately 69A
• 48V system: approximately 35A

Compressors, pumps, refrigerators and power tools may also need additional startup current.

Amps vs Amp-Hours

Amps measure current. Amp-hours measure electrical charge capacity.

A 100Ah battery could theoretically provide:

• 100A for one hour
• 50A for two hours
• 20A for five hours
• 10A for ten hours

The actual result changes with temperature, chemistry, discharge rate, battery age and equipment losses.

Watts vs Watt-Hours

Watts measure power. Watt-hours measure energy.

Watt-Hours = Volts × Amp-Hours

Battery Runtime

Estimated Runtime = Usable Watt-Hours ÷ Load Watts

A 1,280Wh battery running a 100W load has an ideal runtime of 12.8 hours. If 90% of the rated energy reaches the load, the estimate becomes 11.52 hours.

Winter temperature, inverter losses, standby consumption and battery condition can all reduce runtime.

Reading Equipment Labels

Battery Labels

Read nominal voltage first. Then check Ah, Wh, recommended charge current, maximum charge current, continuous output and peak output.

Charger Labels

A charger may have a 100–240V AC input and a 14.6V 20A DC output. Its approximate maximum DC output is:

14.6V × 20A = 292W

Do not combine the AC input voltage with the DC output current.

Inverter Labels

Continuous watts describe normal output. Surge watts describe brief startup capability. Both the inverter and battery must support the intended load.

Appliance Labels

A label may show maximum input rather than average daily use. For refrigerators, furnaces and pumps that cycle on and off, measured energy use is usually more useful than the maximum running wattage.

How to Size an Electrical System

Match the Voltage

Confirm that the battery, charger, inverter, controller and DC equipment use the same compatible voltage range.

Add Running and Startup Power

Convert Power Into Current

At 90% inverter efficiency, a 2,000W load requires approximately 185A at 12V, 93A at 24V or 46A at 48V.

Check the result against the battery BMS, cable rating, fuse, breaker, connectors and busbars.

Calculate Daily Energy

• 100W for five hours = 500Wh
• 500W for two hours = 1,000Wh
• 1,500W for half an hour = 750Wh

Total energy use is 2,250Wh before system losses and reserve capacity.

Common Calculation Mistakes

• Comparing battery Ah without comparing voltage
• Mixing a charger’s AC input with its DC output
• Using inverter surge watts as a continuous rating
• Ignoring startup current
• Assuming maximum current is always being delivered
• Ignoring cold-weather charging restrictions
• Choosing a higher-voltage battery without changing compatible equipment

Conclusion

Begin with voltage compatibility. Next, calculate the running and startup watts. Convert those watts into battery current, and check the BMS, wiring, protection and connectors. Finally, use watt-hours to estimate how long the battery can operate the load.

Vatrer offers batteries for RV, marine, golf cart and off-grid applications. Its lithium golf cart battery conversion kits can be compared using the same voltage, current, power and energy calculations described above.