I recently decided to jump start an old hobby of mine: sewing. When I was about high school age I used to sew lots of things, generally by hand. I had learned how to use a sewing machine in school, but my mom didn’t like me using hers, so I generally did small projects only. I made some little velcro-closure sacks for my marble collection, lots of pillows and other stuff along those lines. I would frequently repair tears in clothes when I was in high school by hand, because I didn’t like clothes shopping and that was a way to avoid it.
It had been my goal for a few years now to learn how to make my own clothes. I decided this was the year and picked up a sewing machine for myself. It took a little bit of doing, but most things came back to me. But what does this have to do with electronics, or anything?
My solar power station sits underneath my kitchen table, and that’s where I set up my new sewing machine. “Should I try to run my sewing machine off the power station?” I actually ask this question a lot when I have some device in my house. It’s fun to be able to run full-size, useful things off of power you generated yourself.
The first question I have to ask is, “do I have enough power to run this device?” This question is generally pretty easy to answer. The inverter on my station converts the DC power from the battery to 120VAC that’s as good as (likely better than) regular household power. Inverters are rated for how much power they can deliver. Often they have two ratings that describe how much power they can supply continuously, and how much power they can supply in a quick burst. My inverter is rated for only 300 watts, and I have it set up to trip a breaker over about 200 watts. Most sewing machines are primarily electric motors (induction motors) and maybe a small LED light and digital display. This won’t approach 200 watts, so I’m safe.
The next thing I have to ask is, “what is the nature of the load being powered?” By this I’m distinguishing between different kinds of loads. There are two main loads you’ll encounter: resistive loads and inductive loads. Resistive loads are very straightforward and easy to understand and identify. Any device that uses electricity to create heat, either as a primary function or byproduct will be a resistive load. Inductive loads can be a little harder to identify, but generally anything with any kind of electromagnet will be an inductive load.
Clothing iron? Has a heating element, no moving parts, purely resistive load.
Desk fan? Has moving blades run by an electric motor. Some resistive heating in the motor coils, but primarily inductive.
Can you guess what kind of load my sewing machine is? Hopefully you said ‘inductive’. In my particular case, the type of load I’m running on my power station doesn’t matter, but there are plenty of cheaper inverters out there that can cause inductive loads to perform poorly, or even damage them. The reason for this is because cheaper inverters create something called a modified sine wave. Hopefully we remember that AC power alternates in the form of a sine wave. A true sine wave is perfectly smooth. A modified sine wave will look like little staircases going up and down approximating the shape of a sine wave, but not perfectly.
For a lot of equipment, a modified sine wave will be fine, but some things especially inductive loads, often depend on a clean sine wave. For something precise and expensive like my sewing machine, I’d never want to run it off a modified sine wave. Fortunately, because my inverter is a more premium pure sine wave inverter, I don’t have to worry. Plus the best part is that I get to say I made my first shirt off of 100% solar power!