It occurred to me that I had spent so much work building something over the past year, and I never once mentioned it on this blog! Some time ago, in the earlier days of this blog, I mentioned all my work on a model solar power project to charge AA batteries. I also mentioned work I had been doing on thermoelectric power systems. I documented many of those experiments and circuits here.
Well late this past winter, I finally jumped on my biggest project yet: A full scale 50-watt photovoltaic power station. I had been dreaming about building something like this for a very long time. Unlike my mini charger, this one would actually be practically useful. I went through many plans and eventually settled on one and then built it. I’m hoping to add many more posts that document some of the finer details of the project, along with how I’ve tested it, what I power with it, things I’ve learned about it, etc. But before I ever get into any of that, I obviously have to show you what it looks like!
I’ve dubbed this thing the Albatross Mk-1. My overarching vision is to have a company that builds these smaller scale practical power systems for everybody. There are other companies out there that build things like this, but they’re expensive, and when you look over the specs, they’re performance is seriously lacking (in my opinion). So I built this beautiful contraption. There are some rough spots (duct tape where I don’t have a proper mounting bracket yet), but overall, it’s well put together and boy is it functional! Let me go over the basic components identified in the photo.
- Samlex PST-300-12 Pure Sine Wave Inverter: This is a really premium quality inverter. This is what takes the 12 VDC from my battery (7) and converts it into 120 VAC wall-socket-style power up to 300 watts. Because it’s pure sine wave, it’s identical to wall outlet power. It may even be cleaner. This costs a bit extra (not that much) but it means I can run anything I want with it and not have to worry about damaging expensive electronics. Modified sine wave inverters can cause problems in basically any electrical device that depends on the voltage waveform being a pure sine wave.
- 15-Amp DC Circuit Breaker: This was an addition I made in place of a standard fuse for the inverter. It allows up to 15 amps (I believe it actually trips around 18-20) to go to my inverter. The fact that it’s also basically a switch allows me to safely connect the inverter to the battery without any sparking. Yes, the 15 amp limit is limiting the output on my 300 watt inverter to somewhere around 180 watts, but for my applications so far, that has been amply sufficient. With some beefier cabling, the 300 watt limit could easily be reached.
- 12 VDC Automotive Socket: This was a recent addition. I use the system to charge things like my cell phone, or my tablet. They don’t take much power, so going through the inverter, and then transforming the 120 VAC back down to 5 VDC for the USB charge power doesn’t make sense. This socket allows me to charge devices as long as I have whatever car adapter is required.
- Genasun 65W MPPT Charge Controller with 5 amp LVD output: This is my favorite component. I actually opened it up when I got it to see inside. It’s so simple, but it does so, so much. Cheaper charge controllers use pulse width modulation (PWM) in order to taper the charge to the battery when it’s getting closer to full. This is fine, and works well. MPPT stands for maximum power point tracking. Basically what this means is that the controller can sense what kind of power is coming in from the panel. Am I getting a strong voltage right now? Ok, how about we drop that voltage a bit and get some extra current. This typically only happens when the panel is cooler, but it means awesome things like I can charge from my 50W panel at up to 3.5 amps. The panel is only short-circuit rated for 2.78 amps. That’s what MPPT is getting me. I love this device! It also has a 5 amp LVD (low voltage dropout) output. This is where I hooked in the 12 VDC automotive socket. The socket is dumb and will have no problem killing my battery (bad!). The LVD makes sure that if the battery gets too low, power is cut.
- 100 amp shunt: This is basically a very precise resistor that is used by a power meter (not pictured) to calculate the power going into and out of the battery. It’s like an odometer for the battery. The shunt itself is pretty simple. Two brass posts, connected by a piece of metal. I’ll have another post later dedicated to the power meter itself.
- Panel Kill Switch: I didn’t actually end up needing this as much as I thought I would. It’s just an inline switch coming from the panel going into the controller. The panel is always making power. Sometimes I need that power to stop if I’m working on the base station. The switch allows me to do that without necessarily undoing any wiring.
- 34 AH (24h rate) Sun-Xtender Sealed AGM Battery: This battery seems small in amp hours, but I have been so impressed with it. It’s a solid rock in my system (literally, it weighs 30 lbs). The AGM means that there’s no liquid, so it’s safe to use indoors. It may vent, but very little. At 50% DOD it will last 1000 cycles (impressive). I typically discharge only 25-30% so it’ll probably last 5 solid years.
- PV Cable: There’s nothing too special about this, but I did want to point it out. This is actually specially designed cable for PV applications. The idea is that this wiring needs to be able to stand up to wild temperature swings (baking in the sun vs. freezing at night) and not fail. I can absolutely attest to this. There were times when the panel and cabling that was outside were literally frozen solid in ice. This summer? They look totally fine, and they bake in the sun. Worth the money (~1$/foot).
A, B, and C are just pointing to some 4-amp quick blow fuses. These fuses serve two purposes. First, they’re there to make sure that the line in question never has more than 4 amps on it. The panel can’t even do this, so that shouldn’t be a problem, but it’s a safety thing. Second, and more importantly, the fuses are there in case two wires coming from the battery are accidentally short circuited. The battery can easily dump dozens or hundreds of amps in mere seconds. These fuses will easily prevent that from happening.
Believe it or not, in all this, I’ve only barely scratched the surface of this system. You’ll notice I didn’t even picture the power meter or panel itself. Those two things are certainly worth posts of their own, and will be soon to follow. I hope you enjoyed this and maybe got some ideas for yourself if you’re building something like this!