Tag: renewable energy

Power Inverter

I have a terrible habit of thinking of projects that would be neat, starting to work on them, then forgetting about them or otherwise leaving them until some point in the future at which I remember them, and then the cycle repeats.  Well, I’ve been mulling one particular project over in my head for a couple years, and now I’m going to declare my intention to start it and hopefully share it with the world: I am planning to build a power inverter.

Now, the truth is I have started on this project a little bit, mostly by sketches on paper and in LTspice, an excellent,  free (but not open source) circuit simulator.  For those unaware (and who didn’t feel like reading the Wikipedia entry), a power inverter (I’ll probably just refer to it as an ‘inverter’) is a device that converts direct current (DC) to alternating current (AC).  There are a number of applications for this…

  • Running household appliances in your car (shave while you drive!)
  • Backing up servers, medical equipment, or whatever else you want to keep running when the power goes out (UPS)
  • Running normal household appliances on a small renewable energy system
  • Connecting your small renewable energy system to the grid

And so on.  Inverters range from small ones you get at a hardware store, to big ones that can run small villages.  I’m not trying to run a village with this project, nor am I trying to power a significant portion of my apartment.  I would, however, like a small, high-quality inverter, and to really learn how it works.  And, I would like to publish instructions for this online, so that hopefully they will be useful to other people and the design can possibly evolve.

Here are my objectives for this project:

  • Output of 120 VAC, 60 Hz (nominal), 300 watts
  • Input of 12 VDC (nominal)
  • Sine wave output
  • Bidirectional: can also function as a battery charger with a transfer relay, similar to an uninterruptible power supply (UPS)

Now, this isn’t really anything novel.  As I mentioned, there are smaller inverters around, and you might be wondering why this would be worthwhile compared to say buying a small inverter at the hardware store for less than $100.  Well, as I mentioned, I’d like to learn, but that’s not all.  Note the ‘Sine wave output’ requirement.  Most of those cheap inverters won’t have this and will thus produce dirtier power.  Also, I haven’t really found a smaller unit that can act as an inverter/charger, which is something that would come in handy for me – while I do have a largish battery with some solar, it would be nice to be able to charge from the grid with this unit and essentially have a UPS.  Of course, I could get a UPS too, but they’re not really designed for continuous usage, they tend to have dirty outputs, and are designed for charging smaller batteries (usually big enough to allow you to shutdown your equipment, or start up generators or whatever).  Also, for safety reasons, I will NOT being setting this up as a grid tie inverter, meaning it won’t sell power back to the power company.

Now, I would also like to point out that I am not sure how well the design I’m considering will scale.  By this, I mean that were I to build a bigger unit (>1kw), I might approach it differently – this is kind of an experiment.  So, if you’re thinking of building something that you can use to power a chunk of your house when the power’s out in the next hurricane, I’d advise pursuing other options at this point.  (Hey, hopefully this can evolve…)  There are actually several commercial manufacturers that make products (inverter/chargers) that are similar to what I’m building, but work at higher power levels.  I have not used any of those companies’ products, but they do have decent reputations.  Also, if your power doesn’t go out very often, and you just want some quick, cheap backup, a normal gas-powered generator isn’t a bad idea.

I should note that I would not consider this the ideal beginning electronics project; while not impossible it will be somewhat challenging, and will involve high (lethal) voltages.  If you’re unsure of things, feel free to ask here (I’ll try to answer as best I can), and go brush up on power electronics (there are plenty of books on this subject, as well as college classes).  I’ll be saying this again, but whatever you try must be at your own risk.  I’ll try to keep up with this and post more as I go, so stay tuned.  It should be fun.

DIY

If you’ve flipped through my previous posts here, you’ve probably seen that I am a bit of a renewable energy buff.  I like messing with solar power, for a variety of reasons.  I like the idea of not blatantly stabbing the environment and contributing to global climate change*, but I also like the idea of making your own power and being independent – electricity is something most people in this country are addicted to without realizing it.  There’s the idea of a quiet, easy source of portable power for fun and for emergencies, and then there’s just the fact that it’s cool.

(*Note: Please don’t start a holy war in the comments over the climate change thing.  There are plenty of places on the Internet you can go to debate/argue/flame for and against this, and so it does not need to happen here.)

Now, some time ago I came upon a magazine called Home Power – I think I may have been in middle school.  This magazine is a journal dedicated to small scale renewable energy, mostly residential.  Its founders purchased land off the grid in the 70s, and turned to solar as a way to not have to run a lawn mower engine to power the car tail light bulbs they used for light.  Because the small-scale renewable energy (RE) industry (responsible for the sale and production of photovoltaic panels, wind generators, control electronics, etc.) was in its infancy when they started publishing the magazine (late 80s), a lot of the articles focused on DIY.  Sure, small operations started creeping up where people offered installation and consultation for RE, but nothing like what you can find now.  A fair amount of progress was made by people playing around with the equipment on their own, sometimes even building their own.  And the Home Power articles often reflected this.

I thought this period in the magazine’s history was awesome.  I loved learning about the various problems these early pioneers had, and how they went about solving them.  I liked seeing what some people did with small systems, and the big systems others built.  It was awesome to see these people working toward solutions to some of the problems faced in the world (and which we still face).

Sometime in the early 2000s the magazine’s tone changed, however.  It was focusing less on the DIY aspect, and more on the ‘turn-key’ aspect – more and more of the systems showcased were belonging to people who didn’t fully understand the technology nor have the desire to.  Rather, due to factors such the cost (and reliability) of electricity in their area, environmental benefits, and maybe the presence of tax incentives, they paid a professional to design and install a system on their homes.  (Note that the last factor I mentioned may also provoke flames; see my climate change note above.)  Not much of a DIY aspect is present anymore.  In fact, it seems that quite a few articles in recent issues are not written by the system owners themselves, but by the system installers/designers, or even third parties.

Now, the truth is that I don’t have anything against people who simply want to make use of RE and don’t want to worry about designing and wiring their system, hoisting panels onto their roof, etc.  Honestly, it would be hypocritical of me.  I mean, I’m a Linux user, and even use Gentoo on my desktop.  And yet I also love Ubuntu for the fact that it presents GNU/Linux as an alternative for normal computer users who don’t care about recompiling their kernel.  (I’m actually typing this on an Ubuntu laptop right now.)  I guess I just miss the old format of the magazine, the one I kind of, well, grew up with.

Now, Home Power is still a good magazine; it’s not like you won’t learn about renewable energy from reading it.  In fact, it’s usually pretty descriptive even if it doesn’t discuss all sorts of homebrew solutions.  You’ll learn about solar power, and if you don’t get as in depth as you’d like you’ll have a good jump-off point for learning more.  They’ll respond to your letters if you have questions, too.  And, their magazine is just well-produced: it’s easy to read, no advertisements in the middle of articles, etc.

What I do encourage you to do, however, is go the extra step.  Yes, you don’t need to be an electrical engineer to use renewable energy, or do anything with electricity.  But there is value in going the extra step and being aware of what is going on with your renewable energy system, or anything.  And guess what: most of the information is out there.  If you’re curious, just go Google-crazy.  Buy some parts or system components, and experiment.  You never know what you might learn.

Fun with Solar Power

I normally charge an 18 AH sealed lead-acid battery to run small things like lights, and to charge my cell phone, radio, etc.  Well a couple months ago this battery died.  It was old, and sulfation had set in. I decided to upgrade to an AGM battery (the old one was a gel cell), and picked out the 49 AH version.  Since I am away at school most of the time, and don’t have the space to take the battery and set up a solar panel I had to wait until this week to go and start solar charging it.  So, here is my temporary setup:

This is just temporary.  I eventually want to get the panel mounted somewhere, and the battery inside.  But this is great for the time being.  The battery does well in cold temperatures (I’ll bring it in at night, of course), and should be able to hold enough that I can rely on the system a little more heavily once it’s more permanent.  This is just one 32 watt panel too, with the other one added it will be even better.