How to Convert Watts to Amps

As more people in the RV and boating circles upgrade their vehicles to include solar, knowing how to measure power storage and currents is important and useful in keeping up with your solar system. The first thing you’ll want to learn about is how much storage your device has and how long you can power your items. Understanding and converting watt-hours to amp-hours is the best way to get started.

Watts vs. Amps

As previously explained, watts and amps do different things concerning electrical power, solar or otherwise. A watt (W) is a unit that measures electrical power whereas an amp measures how much energy or current passes through the electrical line.  Understanding the difference is crucial when setting up and maintaining your solar system.

What are Watt-Hours?

A watt-hour is a unit of measure for the amount of power over some time. For consumer purposes,  if something uses 1 watt (W) over four hours (h), that item's watt-hours (Wh) would be 4Wh.

A common example would be lightbulbs. The average lightbulb contains 6W. If you had a 60Wh battery powering the lightbulb, and only the lightbulb, the battery would be able to keep the light on for 10 hours.

What are Amp-Hours?

An amp-hour measures the current that draws from the device over an hour. It’s not a measurement of energy, but rather of charge. If you have a 100Ah battery, that means it can release 100 amps (A) of energy in one hour (h). The amount of time factors into how much amps is used. To continue with the example, if your 100Ah battery is only used for half an hour, it can double the amps drawn during that time to 200A instead of just 100A.

Conversion Formula

Understanding the amp-hours or the watt-hours of your battery and system is important in estimating your load and run time.  Finding out the amps or watts of an item isn’t difficult to do so long as you have one of the measurements (Ah or Wh) and the voltage of the system.

Converting Watt Hours to Amp Hours

If you need to find how many amp-hours your electrical system can deal with and you don’t know the amperage right off the bat, you can convert the watt-hours to amp-hours by using the following formula:

To put it into an example, let’s use the 12V Lithium Iron Phosphate Battery which has 1280Wh and 12.8 nominal voltage (V). Plugging the numbers into the formula, you get:

Converting Amp Hours to Watt Hours

To discover battery sizes, wire thickness, solar system design, or any other facet of your solar setup, you need to find out your amp-hours. Converting amp-hours to watt-hours is just as simple as the other way around. You only need to know the amp-hours and the voltage of the system.

To convert amp-hours to watt-hours, you effectively do the opposite of the previous formula:

Using the same Sunrich battery as an example, you would plug in the am-hours and voltage:

This simple equation will save you a lot of trouble when setting up your system.

Practical Applications

Battery Capacity Estimation

Probably the biggest reason anyone might need to have a basic understanding of these conversions is to intrinsically know a battery’s energy capacity. Knowing how much battery capacity a device uses gives you a better understanding of not only how much you fully need for your system.

Electrical System Sizing

When setting up your electrical system, whether it’s solar, hybrid, or other, the first thing you need to know is how many watts you use in a day. By adding each of these items together and converting it to amp-hours through the conversion formula, you’ll know the size and type of batteries you need, the panels required to charge them, the thickness of the wires, your inverter, and everything else your system needs.

Solar System Design

Knowing the full size of your electrical system will keep you aware of the options available to you. You can make informed decisions about your system, what to buy, and how much you need for everything. Between deciding battery sizes and the types of solar panels you want, you can estimate the measure and cost of your system accurately.

Advanced Conversions

Dealing with larger units means dealing with higher numbers, which means having to handle more advanced conversions. In essence, when you have a larger system, whether it’s a large house or a business, you’ll be dealing with kilowatt hours (kWh).

A kilowatt hour is 1000 watts discharged over 1 hour, similar to a watt-hour but bigger. To find the kWh from the watt-hours (Wh), just divide the Wh by 1000 to receive the kWh.

After that, we adjust to the larger number and use a similar formula to calculate the amp-hours (Ah). To do so, we multiply the kWh by 1000 and then divide that number by the volts:

Using Sunrich’s 12V battery as an example once again, plugging the appropriate values into the spaces, the formula will look like this.