Electricity Basics

Understanding

It’s easy to be confused by electricity and the onion of understanding has many, many layers. Here we aim to go just deep enough to be practical.

Voltage is electrical pressure

Start with voltage: electrical pressure. Remember that. Voltage is pushy. More voltage = more push. Car salesmen are high voltage, high pressure. Roll that on your tongue a few times “voltage is pushy.” Remembering that one trait will grease the rails of understanding. “Voltage is pushy.”

At this level of understanding water is a great analogy. Voltage is like water pressure.

At higher voltage there’s more flow. Flow is called current. Think of a water hose. If your water pressure is high, you’ll get more flow: more water shoots out quickly, great for watering launch fields. Squeeze the water hose and you introduce resistance. Water flow reduces. That’s what a resister does in units called “Ohms”, abbreviated Ω. The spigot on a garden hose is just like a resister.

If you put a little propeller in the hose, facing current flow, it would spin and could be geared to do useful work. It’s also has resistance. A smaller hose has a lot of resistance than a larger one. The same is true for electricity. A small wire has more resistance than a larger one.

Think about a bucket with a hole near the bottom. With an inch of water in the bucket there’s not much pressure at the hole. But fill the bucket up full and there will be more pressure, ergo more water flow (current) through the hole.

Let’s stick with the bucket analogy. A higher level of water means more pressure (voltage) at the outlet. Once you know that voltage is pressure, the rest makes more sense. If you have a lot of voltage, more current will flow.

Repeat after me, “Voltage is pressure,” like a high voltage car salesman: he’s high pressure.

Load

Put a wire across a battery and you “short it out.” Lots of current flows because there’s almost no resistance and the wire gets really hot, maybe even glowing (remember those “incandescent” light bulbs?). That wire represents a path for current or “load”. Not a very useful one, admittedly.

Hook the battery up to an electrical motor—a far more useful load. How much current flows depends on the input voltage (pressure) and the motor’s resistance. All loads have some amount of resistance. That short-circuiting wire had very little. A motor typically has relatively little. That’s why so much current flows if you hook a full battery up to the motor.

A resister put across battery terminals is another type of load albeit not a very useful one. Current will flow based on battery voltage and resistance. Put a bunch of loads across the terminals and you get a lot of current flow. This is called putting the loads in “parallel”. The battery strains to keep up Its voltage.

Battery “Straining”

As we put loads across a battery its output voltage drops because of the batteries internal resistance. Otherwise, putting a wire across the terminals would cause infinite current which isn’t possible.

Math

Of course there are formulas.

Voltage (V*) is pressure—yup, volts. Have we mentioned that voltage is pressure?

Current (abbreviated I) is flow in amps.

Power in Watts (W) = pressure (volatage or V) times flow (amps or I).

In other words, Volts x Amps is power. Your US house voltage is around 110 volts. If 3 amps is flowing through a circuit, it’s using 330 watts (110 volts x 3 amps).

Your paramotor starter uses a 24 volt battery. If it draws 20 amps during start that’s 480 watts.

Lets say your electric paramotor likes 100 volts. If we run 50 amps through that we’re consuming 5000 watts. Can that be related to horsepower? Yup. Directly. Google “5000 watts in hp” and you’ll get about 6.7 hp. Notice that at 50 volts you would need 100 amps to get the same power. File that away.

Wire has resistance per distance. Thinner wire—or more of it—increases resistance. Much like a hose. A skinny hose, or lots of it increases resistance. Resistance is friction so it heats things up. That’s bad unless you’re making toast. Toaster wires have a high resistance and make use out of the heat. But when running our electric paramotors we don’t want heat.

Think about straws. It’s easier to blow through fat straw than a skinny one.

Another interesting formula relates resistance to power:

Power (Watts) = Resistance (R) x Current (I)²

Well that’s interesting. When relating power to resistance, power goes up to the square of current. Having to push current through a wire consumes power but notice that it’s related to current not voltage.

But if we want to USE the power, we can either use high voltage and low current, or low voltage and high current. So if we increase the voltage, current flow goes down. And it’s current flow that dictates how much power is used in the wires. THIS is why electric grids have such high voltages on cross-country wires.

Lets say our wiring represents 1 ohm of resistance. At 100 amps, the amount of power used (wasted) in transmission is 1 ohms x 100 amps SQUARED (100² is 10,000) or 10,000 watts! But at 50 amps it’s only 2500 watts.

Wow, that’s a HUGE difference.

You can see why it’s so much better to have higher voltage and lower current if wire resistance is much of a factor.

*A common abbreviation for voltage is also E

Doing Work

Lets say at full power our motor(s) draws 50 amps at 100 volts.

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