Watts, Volts, and Amps

Batteries, Electric Motors, Solar Panels, Generators, and Wind Generators all have one thing in common, their outputs are typically measured in Watts?

Why watts and not amps or volts? Well, the answer is actually rather simple: watts don’t change depending on your setup.

You see, Watts, Volts, and Amps are linked in a mathematical formula. W = V x A

From this formula, you can determine the third value when you are only given 2 of the values by way of simple algebra (and you thought you would never need to use it again)

To not bore you with math, I will surmise to say that as volts and amps fluctuate inversely to each other (as volts climb by a factor, amps decrease by the same factor) watts remain unchanged!

For example (I couldn’t resist):

100W = 12 volts x 8.333 amps
100W = 24 volts x 4.166 amps
100W = 48 volts x 2.08 amps

So, when you purchase an electrical device, they can simply tell you how many Watts it produces or consumes, and the way you wire it will determine the voltage and amperage that it will operate.

To take this further, with electric propulsion, you will see the motors listed in the form of kW instead of Horsepower. The reason is the same, as the motors can come in a whole range of voltages, as low as 24 volts and well up over 96 volts! By listing the motors output in kW, they are uniform and comparable.

For example, a 48v motor that is rated at 20kW will draw 416.6 amps at full throttle. A 96v motor that is rated at 20kW will only draw 208.3 amps. In the end, it is the same amount of power being moved, just at different voltages and amperages.

So remember, next time you look at an electrical gizmo for your boat, consider rating it in watts to compare one device to another instead of looking at the amps it produces or consumes; you might get tricked up by the voltages. Then you can compare the cost of these items with the watts they produce or consume and spend your money in the most effective way to get as many Watts as you can out of each dollar.