Discussing electricity can become a charged topic in RV and boat circles. But many campers and boaters are adding solar solutions to and upgrading their electrical systems, so possessing a basic understanding of measuring currents, energy, and storage can be helpful. Let’s see if we can break down a few barriers and spark a conversation about turning watt-hours to amp-hours.
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What is a Watt-Hour?
A watt-hour (Wh) is a unit of energy that measures the capacity of power (in watts) moving over time (an hour). When talking about battery life, this would mean the number of watts that an application uses per hour.
So, if an appliance is rated at 100W, it will use 100W of power in one hour and 200Wh in two hours. Conversely, if you have five 100W devices running for one hour, they would use 500Wh in total.
Here’s the equation: (total number of watts) x (total number of hours) = watt-hours.
So, if you have a 60W bulb and you’re trying to calculate how many watts your bulb uses in 24 hours, your equation would read 60 watts x 24 hours = 1440 watt-hours. Or, to use the abbreviated measurement, the answer would be 1440Wh.
What is an Amp-Hour?
An amp-hour is a measurement of current (in amps) flowing over a period (an hour). This measurement tells you the number of amps a device draws when you use it for an hour. It’s expressed with the abbreviation “Ah.” Amp-hours is not a measurement of energy, but rather a measurement of charge. Because voltage is not included in an amp-hour, you cannot calculate energy from amp-hours alone.
If you have an 100Ah battery, this means it can expend 100 amps of energy in one hour. However, if you only use that 100Ah battery for half an hour, it can give 200A during that 30-minute draw (if the battery operates at 100% efficiency).
How Do You Convert Amp Hours to Watt Hours?
When measuring your RV electrical system requirements, you’ll need to convert watt-hours to amp hours. This will assist you in deciding on the voltage you will use, battery sizes, and even the thickness of wires for your solar system design, etc.
The equation is watt-hours = amp-hours x volts.
In this instance, if you don’t know the number of watts, you’ll multiply the total number of amp-hours times the voltage.
→ Need a quick refresher? Check out Amps, Volts, and Watts: Differences Explained
As an example, if you have a 12V battery for your RV, and your device is rated for 100Ah, you’ll need to multiply the amp hours by the volts: 100Ah x 12V = 1200Wh.
To showcase how amp-hours does not equal energy, you could get the same 1200 watt-hours from a 24V battery. You’d multiply: 50Ah x 24V = 1200Wh.
How Do You Convert Amp Hours from Watt Hours?
On the flip side, if you need to discover how many amp-hours (Ah) of current your electrical system can handle, use the following equation: amp-hours = watt-hours / voltage.
Let’s look at an example. If you’re not sure your battery’s amp hours, but you know the watt-hours are 120, and the voltage is 12, you can calculate the amp hours: 100Wh / 12V = 10Ah.
How Many Watt Hours in a 100 Ah Lithium Battery?
To answer this question, we need to know the battery voltage. Let’s assume it’s a 12V lithium battery. Using the equation above, watt-hours = 100Ah x 12V. This means the battery’s capacity is 1,200Wh.
Note that amp-hours will vary slightly depending on nominal voltage. In a 12V Battle Born Battery, this is a little over 13V so we see around 1,300Wh of available energy. This is partially why comparing battery amp-hours isn’t apples to apples.
In the video below, Tom Morton of Mortons on the Move compares “apples to apples” between lead-acid and lithium batteries with watt-hour capacities. He finds out just how difficult it is to get the energy ratings out of lead-acid that they claim and just how much lithium batteries provide under various loads.
He also demonstrates that, over the life of one of our Battle Born Batteries, the cost per watt-hour of energy is less than all of the tested lead-acid competitors! See the results here: What is the Best Battery for the Money?
Where Can I Find an Ah to Wh Conversion Chart?
To help you with some quick and common amp-hour to watt-hour conversions, we’ve pulled together this handy chart for quick reference. Note that the watt-hours are with a 15-hour discharge at 70 degrees F, as energy capacities of batteries vary greatly with discharge and environmental conditions.
There are many conversion calculators and charts that you can find with a quick Google search.
But knowing the equations yourself will help you add watts of several devices together to determine amperage needs for your RV. You never know when you’ll need to understand your battery’s power needs, and you don’t have cell service to look it up.
When Will You Need to Make Watt- and Amp-Hour Calculations?
The biggest reason you’ll need to understand these calculations is to understand your battery’s energy capacity. When trying to run a device on battery power, it’s important to understand how much battery capacity you’ll need to run it.
You might also need to equate watt-hours to amp-hours when designing your solar setup. You’ll determine how many watts you’ll use in one day, adding each device’s watts together. Then you’ll divide that total by the voltage in your rig to discover the amp-hours that will be created. This figure will determine the number and type of batteries you will need, the size of solar panels required, and even the thickness of connecting wires.
Knowledge Is Power
By understanding how amp-hours and watt-hours are related, you can effectively compare battery energy capacities. While multiple types of batteries are rated for “100 amp-hours,” you now have the knowledge to figure out just how much energy those batteries will provide you and for how long. If you ask us, that’s some pretty crucial knowledge when you need power off the grid.
Want To Learn More About Electrical Systems and Lithium Batteries?
We know that building or upgrading an electrical system can be overwhelming, so we’re here to help. Our Reno, Nevada-based sales and customer service team is standing by at (855) 292-2831 to take your questions!
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