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Convert Watt-Hours to Amp-Hours

By SSK Admin December 09, 2022

Converting watt-hours to amp-hours is one of the most useful watt conversions you can use when building a solar system.

It allows you to know the size of battery you need in an off-grid solar system and gives you an understanding of how much power you’re using.

Join us as we dive deeper into the conversion and break down everything you need to know about watt hours and amp hours.

Watt-Hours

Watts are a measure of power based on the rate of electrical energy being dissipated, and watt-hours refer to time. In other words, watt-hours measure the number of watts discharged over an hour.

convert watt hours to the amp hours

In most cases, you use watt-hours as a measure of your solar needs.

It gives you an understanding of how big your solar system needs to be for you to power the appliances in your home.

However, watt-hours can’t simply be read off a label. The calculation requires you to obtain the two components as individual variables first.

Once we have those two variables, we know how to convert watts to watt-hours.

How to Find Watt-Hours                            

Knowing how to retrieve watt hours allows you to size your system based on your solar needs.

Firstly, you’d want to make a list of all the appliances you want to run off your solar system. This includes everything from computers to lights, to something as small as phone chargers.

At the back or beneath almost all appliances are a label with power ratings. Chances are that there are a few ratings on the label, but we’re interested in the output wattage for that appliance.

This can either be in the form of watts, volts, amps, or milliamps. The one that we want to focus on would be the watts. If you need to, you can collect the other units and use our VA to watts calculator to do the equation the other way around.

However, if the other measurements are given and the watts are missing, don’t panic.

Using Ohm’s Law or a Watt’s law calculator allows us to convert other units of power to the one we desire. 

Watts is equivalent to saying volts multiplied by amps. So, if a phone charger is measured at 13 V and 1.3 A, the total output would be 16.9 W.

If the power rating is milliamps, we’re interested in amps if we want to get the watts. All you need to do is divide the milliamps by 1,000 to obtain the amperage of the appliance.

However, if you’re wanting to make use of the watt hours to milliamp hours calculator at the end, you can keep this measurement as is.

Once you’ve got the output wattage of all the appliances you want your solar system to power, you want to figure out for how long you want them to be powered. This will be recorded in hours.

Watt-hours is simply taking the output wattage of an appliance and multiplying it by the hours per day.

convert watt hour to amp hour

It’s important to compensate for the number of similar appliances being used.

For example, if we have two DC lights measured at 20 W being used for 3 hours, it would be 120 watt-hours per day for that set of lights.

Once you’ve finished multiplying the output wattage and hours per day of every appliance, you sum up the watt hours per day of each device.

Now you should have the total watt-hours that your system will use.

Using an off-grid solar calculator, this variable can be used to size your solar system’s components.

This includes everything from the battery used to store power, to the solar panels being used to harness energy from the sun.

Before we dive into the watts to amp hours calculator, we need to look at where we would use amp hours.

Amp-Hours

When trying to figure out amp hours, the term capacity gets thrown around a lot.

Capacity refers to the quantity of electricity that can be extracted from the battery from the cycle of fully charged to discharged. But how is this measured or determined?

Well, similarly to our appliances and their power ratings, a battery’s power rating is read from a power label.

Batteries will have a range of ratings on them, from the voltage to the amp hours. We’re interested in the amp hours, or the amount of energy in a battery that’ll give you 1A per hour.

All batteries have a predetermined capacity that they can disburse under normal circumstances. This measurement is amp hours.

But let’s look at a more practical example.

Finding Amp-Hours

If you have a battery that has a capacity of 1 amp per hour and you’re using an appliance drawing a steady current of 1 A, then the battery will be able to power that appliance for exactly 1 hour.

Taking this hour, converting it to 60 minutes, and then diving it by 10, we get a value. This value tells us that every 6 minutes, the battery charge will deplete by 10%.

convert watt hours to amp hour

Let’s look at a more another example and up the battery capacity to 240 mAh.

If we’re powering an appliance that’s drawing a steady 50 milliamps, some simple division will tell us that the battery will run for about 4.8 hours.

Converting the 4.8 into minutes gives us 288, and dividing this by 10 lets us know that the battery depletes by 10% every 28.8 minutes.

These calculations are all based on ideal conditions, not taking into account the ambient temperature, current peaks, or cycling of the device. 

If you want a more accurate answer then using an online amp hour calculator would be your best bet.

However, the answer should still be close enough for you to use the value in an equation or as a general reading.

But now back to the million-dollar question, how do we convert watt hours to amp hours?

Watt-Hours to Amp-Hours  

If we used ohms law to obtain the watt hours for solar needs, we can use it again as we’re still working with watts, amps, and volts. 

The only difference now is that we’re adding hours into the mix.

As an example, let’s assume we want a battery like the AC200 Max Bluetti in our solar system. This bad boy is measured at around 2,048 Watt-hours, with a voltage of approximately 51.2 V.

convert watt hour to amp hours

Knowing these two values allows us to determine the amp hours using simple division.

Dividing the 2,048 watt-hours by the 51 volts gives us exactly 40 Amp-hours.

Now you know how to convert watt-hours to amp-hours, and vice versa.

Conclusion

In the world of solar energy and electrical appliances, maneuvering your way around the different measurements of power can be achieved using Ohm’s law.

If you have two of the three variables, the one you’re looking for can be found using the multiplication or division of the other two.

Knowing these conversions is essential if you want to know what your solar system can power and how much power is being drawn from the appliances. 

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