You don’t have to go far into researching a mobile office before realizing that you will probably, no, definitely, need a power inverter. So, it's important to know how to choose the right power inverter for your needs.
Choosing the right power inverter can seem quite overwhelming, but don’t worry, we’re here to help. In this article, we will explain how inverters work, why it’s important to choose the right one, and how to choose the right power inverter. We've also interviewed Bob Hanks, of Fleet Electric, aka, the expert in this area.
We'll be highlighting important keywords and phrases, so you know to pay attention to those parts.
Well. Where should we start? I say we head back to high school physics.
Background: Electricity
Copper is a conductor. This means it can carry, or “conduct” electricity very easily.
As you can see, copper has electrons, i.e., the little dots on the rings.
The Protons and Neutrons you might be thinking of? They’re hiding in the nucleus, the brain, which is the sphere in the center. But they’re irrelevant for us at this moment, so don’t worry about them.
Looking at this copper atom, all the rings look happily filled. . . except the outermost one. The rings of an atom like to be filled up a certain amount, but this ring has one electron, and he’s lonely. He’s looking for a buddy everywhere, randomly. He’s called a free electron, because he’s free to look for other electrons to be “friends” with (i.e. share a ring with and therefore bond the two atoms together).
But a randomly moving free electron by itself has no use for us. Unless… we can make the electrons move in one direction. (Spoiler alert: we can.)
Voltage “pushes” the electrons in one direction, and this flow of electrons is called a current.
We need a complete circuit to do this effectively. A complete circuit is a closed loop, where the electrical current flows from the battery to the component (which is the device being powered), and back to the battery once more. It will either flow from positive to negative, or negative to positive. As we continue, you will begin to see why this knowledge is helpful in how to choose a power inverter.
Key Takeaways:
- Free electrons move randomly, which is not useful; however, we can make them flow in one direction with voltage, creating an electrical current.
- Translation: Voltage makes electrons behave. We can use it to create an electrical current, i.e. a flowing river of electricity.
Got it? Good. We’ll move on to direct currents.
Direct Currents (DC)
Let’s talk about direct currents. They’re used in batteries most notably and are also the type of current produced by solar panels. Most importantly for us, direct currents are used in car and auxiliary batteries. Which you will use one or both of to power your mobile office.
DCs move in one, direct, direction, from one terminal to another. Think of them like a lazy river in a waterpark, flowing in one direction, through a loop.
A terminal is an entry/exit allowing an electrical current to move inside and/or out of a power source. Think of them as doors that can be open or shut, allowing, or not allowing, an electrical current to pass through a power source.
A battery has two of these terminals. It can flow from the positive terminal to the negative terminal, or vice versa. Those + and - signs on batteries? That’s about this.
Another thing to know is the direct current’s waveform. It’s a straight line. This line can be in a positive position, a neutral position, and a negative position. This is caused by the flow of electrons. Flowing from a negative terminal to a positive one produces a positive voltage. Flowing from the positive terminal to the negative terminal produces a negative voltage. (Note: this is from the electronic technician perspective, not the electrical engineer perspective, which says the opposite).
Key Takeaways:
- Direct Currents move in one direction, from one terminal (door) to another.
- From the electronic technician perspective, flowing from a negative terminal to a positive one produces a positive voltage, and flowing from a positive terminal to a negative one produces a negative voltage.
- Direct Currents are important because they can be transformed into alternate currents through a power inverter.
Alternate Currents (AC)
You know how we said direct currents moved in one direction? Well alternate currents. . . don’t. They’re constantly flowing forwards and backwards, with rising and falling intensity. If direct currents are a lazy river, think of alternate currents like an ocean, with high and low tides.
We’re going to be using a math term you may remember from trigonometry: sine.
Alternate currents produce sine waves. A sine wave is a curve that goes from neutral, up to its maximum, back to neutral, down to its minimum, and finally, back to neutral. Then, it repeats. I’ll show you a picture, so you’ll understand it better.
Every time this cycle is completed, it is one rotation. One full rotation is notated on the picture, by a bracket and two arrows showing the beginning and end.
Frequency is how many rotations are completed in a second. So if I said “the frequency is 60,” that would mean that 60 rotations are completed in one second.
Key Takeaways:
- Alternate currents create sine waves
- Sine waves have a distinct shape, shown above.
- Frequency means rotations over seconds.
Why Do we Need the Inverter?
I want you to remember the sine wave we just learned about. Look at its shape, its curves.
We know direct currents don’t make those curves. DCs are graphically straight lines; when the power is “on”, it transforms from a neutral line to a positive or negative line.
This is why it's important to know how to choose a power inverter, as they are necessary in mobile offices. Since DC and AC waves act so differently, one staying pin straight while the other oscillates in waves, not many devices can be compatible with both.
To fix this, a power inverter takes a direct current, and manipulates it to imitate a sine wave.
For mobile offices, a power inverter takes the direct current of the car’s battery, or solar panels, and imitates a sine wave that your laptop, computer, and printer can use.
How Does the Power Inverter Work
How does it do this? Well, I’ll explain!
First, let’s recall our memory of direct currents. DCs, when plotted on a graph, are a straight line. When powered, they become a positive or negative line, depending on the flow of electrons, and return to neutral when the power is off.
The power inverter receives the battery’s DC flow of electrons and mimics the AC’s sine wave. It does this through switches, called IGBTS, that move rapidly at specific intervals, and control the flow of electrons, making them go forwards and backwards like an alternate current.
There can be two types of power inverters. The kind we just talked about, with the switches at set intervals, create modified sine waves.
You can see a picture of one above; it’s the orange line. This line is truly a modified sine wave. You can see that it resembles a sine wave, except much less curvy. Hence the word “modified”. Some people refer to them as “quasi sine waves”.
Modified sine waves are kind of like a puzzle piece that nearly fits. They’re close enough to a real sine wave for most appliances, but not all. Intricate electronics, particularly, need a pure sine wave to function properly. They need a perfect puzzle piece fit, whereas other devices can mash the “puzzle piece” into their puzzle and be fine.
If something is powered by a modified sine wave, and it is not compatible, it can cause electrical noise, stress to the machine, heat buildup, and even damage. Pure sine waves don’t have this problem since they are practically identical to alternate currents. However, pure sine wave inverters are typically pricier than their modified counterparts. If you’re planning to power a laptop, you should still opt for the pricier pure sine wave inverter, since a modified sine wave inverter could potentially damage it.
Now that we know the difference between modified and pure sine waves, how do we get a pure sine wave?
Pure sine waves are made by something called pulse width modulation. Like modified sine wave inverters, IGBT switches are used to mimic a sine wave. Except, this time, they go quicker, and at variable lengths of time, called “pulses”, that average out to match a true sine wave. Pulse width modulation is more accurate, so much so that it creates a wave that is compatible with all AC appliances, including your laptop. But that accuracy has a price, hence why pure sine wave inverters are more expensive than modified power inverters.
Now you’re probably wondering, should I get a modified sine wave power inverter, or a pure sine wave one? Let's look into some more information on how to choose a power inverter.
Which Power Inverter Should I Get?
First off, it’s important to think about what devices you plan to power with this inverter. Does your list include a CPAP machine? A laptop? Any intricate electronics? Do you plan to power a mobile office? If so, you should bite the bullet and pay for a pure sine wave inverter. Modified sine wave inverters are just not worth the risk of damage to your expensive electronics.
Another thing you should consider is how powerful you want your inverter to be. To do this, you need to do a little bit of math.
Another thing you should consider is how powerful you want your inverter to be. To do this, you need to do a little bit of math.
- The first thing you should do is determine the maximum number of devices you’ll be using at one time and list them.
- Next, you need to calculate how much wattage you’ll be using. Look at each of the devices you listed in step one and note their wattage. It should be on the packaging. Once you’ve collected all your wattages, add them up.
- Hint: if your device doesn’t detail their wattage, you can calculate it with this formula below.
- Volts • Amps = Watts
- Another thing to watch out for is peak surge. Peak surge is the initial surge your device draws when starting up. Some devices can draw up to three or four times amount of their running wattage during peak surge! Look up your devices’ peak surge online and add it to your total wattage.
- Hint: if your device doesn’t detail their wattage, you can calculate it with this formula below.
- Got your total wattage figured out? Cool! But we’re not done yet. Finally, you need to add a buffer. A buffer of at least about 25% should suffice. You can calculate your total wattage, with an added 25% buffer, below.
- Wattage • 1.25 = Total Wattage with 25% buffer
- Note: We recommend adding a buffer to protect your inverter. You should avoid using your power inverter’s maximum load, because it will be very difficult for the machine.
Tips From the Experts
I sat down with Bob Hanks from Fleet Electric to ask him how to choose a power inverter for varying needs. And boy, is he knowledgeable!
Bob says that the two most common mistakes he sees people make with power inverters are these: buying bad-quality inverters, and not paying attention to the manual.
Let’s go over the first one.
When buying a power inverter, Bob says you usually “get what you pay for”. Inexpensive power inverters tend to be lesser-quality and may lack the safety features you would get with a higher end model.
Low-quality inverters may have operating temperatures that aren’t compatible to the seasons they’ll be subject to. In the winter, it might be too cold for it to operate, and in the summer, too hot.
Another important feature you may or not have depending on the quality of your inverter is a ground fault circuit interrupter, or GFCI. This is a feature that can save your life. A GFCI senses when a person’s body is undergoing a shock and stops the power before the person can be injured or electrocuted. Please make sure your inverter has a GFCI.
Bob’s next tip in how to choose a power inverter is to closely follow the manual. Many people have installed their inverter incorrectly by not following the instructions in their manual. This is important because correct installation protects your inverter from unnecessary damage, and costs. Bob particularly warns people to pay attention to their manual when it says to install your inverter in a cool dry area. Heat and water are “big killers” to your inverter, says Bob, and storing your inverter in the proper location prevents damage.
Final Thoughts and Review
Okay! I think that about covers it. Now you know what direct and alternate currents are, and how a power inverter converts them from DC to AC. You also know what kind of power inverter you need, and why it’s important you get that specific kind for you. If you have any further questions on how to choose a power inverter, be sure to visit our contact page to reach out to our mobile office experts.
Leave a Reply