Why Phone Chargers are Measured in Watts Instead of Amperes

Phone chargers are typically measured in watts (W) rather than amperes (A) because watts provide a more comprehensive understanding of the charger's power output. This article explains why watts are more relevant for charger specifications, including power delivery, voltage variation, efficiency considerations, and compatibility. Additionally, it discusses the transition from fixed voltage chargers to modern adaptive fast charging schemes.

Introduction to Watts and Chargers

When evaluating phone chargers, the primary metric that matters is how effectively they can charge your device. This is where watts (W) come into play. The formula for calculating power in watts is:

Power (W) Voltage (V) x Current (A)

Power Delivery

The power in watts is key to understanding the total power a charger can deliver to a device. This is crucial for determining charging speed. For instance, a 20W charger can deliver more power than a 5W charger, allowing it to charge a device more quickly. This is why a 20W charger can be more beneficial for high-power devices or those requiring faster charging.

Voltage Variation

Modern devices often support a range of voltages for charging, commonly 5V, 9V, and 12V. By specifying the power in watts, manufacturers can communicate the charger's capabilities across various voltage levels without needing to specify the current separately. This standardized approach ensures that users can easily compare chargers based on their power output.

Efficiency Considerations

Using watts to measure the power output of chargers also allows for a more accurate assessment of the charging process's efficiency. Knowing the wattage helps consumers compare chargers and understand which ones are more efficient in terms of energy usage. This is particularly important for users who are concerned about their device's battery life and power consumption.

Compatibility and Adaptive Charging

Many modern devices use adaptive charging technologies. These technologies adjust the voltage and current based on the device's needs. By measuring in watts, consumers can assess the maximum power output of chargers regardless of the exact voltage and current combinations used to deliver that power. This standardized metric ensures compatibility and provides a clearer indication of a charger's performance.

Transition from Fixed Voltage to Adaptive Fast Charging

Back in the day, phone power adapters used to be rated in amps, operating at a fixed 5 volts. However, with the advent of adaptive fast charging, the voltage can now vary between 5 volts and 15 volts. This variability makes it simpler to refer to the power output:

For instance, my previous phone used 9 volts and 2 amperes, resulting in a 18W charger. My current device supports 5 volts and 4.5 amperes, giving a 22.5W output. Simply looking at the amperage can give a misleading view of the charger's speed and power delivery. Therefore, manufacturers and consumers benefit from using watts to measure charger specifications.

Conclusion

In summary, measuring phone chargers in watts provides a clearer and more useful indication of their performance and compatibility with various devices. This standardized metric ensures that users can easily compare chargers and choose the most appropriate and efficient option for their needs.