Voltage, current, amps, watts, AC and DC….all common electrical terms. There are many online resources that explain them at a technical level. Our goal isn’t to be another one of those. Instead, we’ll describe these key terms with some basic analogies. Simple.

Electricity Basics

Voltage (V) is like the pressure that pushes electricity from the source to anything that needs power. Think of voltage as the height of a line on a grid. The higher the line, the higher the voltage.

Current is measured in amps (A). It’s the flow rate of electricity. If something needs a lot of power, like a cooktop, then the flow will be high. Current is the thickness of that same line. 

Imagining power as a line drawn on a grid, these three lines show both voltage and current. The higher the line on the grid, the higher the voltage. And the thicker the line, the higher the current.

Watts (W) is a voltage-agnostic measurement of the work that electricity does in an instant, calculated by multiplying voltage x amps. This is important because different voltages can produce the same watts if the amps are adjusted: a 1200 watt load can be powered by 120V at 10A or by 12V at 100A. 

These two lines represent two 1200 watt loads – see how the voltages and amps are different?

AC and DC are different types of voltage. 

• DC (direct current) is a straight line of electricity, as illustrated above. 

• AC (alternating current) is a wave. Using the above analogy, amps is still the thickness of the line, and voltage is the height of the AC wave. 

A multimeter measures voltage – how high the line is above 0 for both AC and DC power. It does not measure current. 

Why does this matter? Your house batteries consume and provide DC power, while shore power comes into the van at 120V AC. Each device in your van has its own electricity needs – some AC and some DC.

Measuring Capacity & Work

Watts and amps tell us about power at a single moment in time. To describe power over time, we use amp hours (Ah) and watt hours (Wh) to indicate the amount of work done by something like a solar panel, or the amount of energy stored in the battery. Just like amps and watts, amp hours and watt hours are closely related.

Our preferred way to measure power over time is Wh because it is voltage-agnostic. Remembering that amps x voltage = watts, watt hours is simply amps x voltage, over time. It’s a great way to estimate how long something can be powered or will take to charge.

For example, a 1000Wh battery can provide 1 watt for 1000 hours, or 500 watts for 2 hours. If charging, a 200w solar panel could charge that 1000Wh battery in 5 hours if the battery is totally empty. (Remember that these examples are all IDEAL and assume that there are no losses, perfect sun, all conversion is 100% efficient, etc.)

Bringing it all together: volts, amps & watt hours

Imagine your battery is a 60 gallon empty water tank. You have one hour to fill it. 

You can move one gallon at a time in a bucket really quickly from your water source to the tank.

Or, you can move 60 gallons once in a truck, moving slowly from your water source to the tank.

Each example results in a tank that was filled in one hour. So, even though the size of the vessel changed, each method accomplishes the same amount of work in one hour (moving 1 gallon/minute). This is watt hours.

In the first example, imagine the speed you moved is voltage (high voltage), and the size of the bucket you carried is amps (low amps).

In the second example, you had low voltage and high amps.

These different pairs of voltage and amps accomplished the same thing in one hour. This is why it is important (especially when comparing things at different voltages) to use watts and watt hours rather than amps and amp hours.

This relates to your power system because you may need to know how long your batteries can provide power based on the amps and voltage of a particular load. We'll talk more about electricity and van power systems in a future post.