Solar Generator - 7320 Wh

----------- I'm still adding to this, just wanted to get the main info posted -------------

Initial post: February 7, 2025

Last update: March 2, 2025 - added parts list and source links, tracker base construction notes,minor corrections.

I built a 12 volt solar generator as a proof of concept to see how closely reality matched the various claims made in videos and manuals. I tested the generator by letting it charge and run a small refrigerator, electric blanket, coffee maker and some lights. This worked well and I feel comfortable taking at least the battery pack along with me to go car-camping.

However, this battery pack would not run my small microwave. The battery voltage would drop below what the inverter could handle. So, while the results of that project were useful for certain limited situations, it wouldn't work as a true power backup option. Therefore, on to version 2.0

Initially I ordered four 305 Ah cells for version 2.0, but then reconsidered and ordered 4 more. In the course of researching this subject, I came across various discussions about 12-volt vs 24-volt vs 48-volt systems. The higher the voltage, the more fixed the solution, however the wires got thinner. 12-volt systems are great for cars and small RVs and boats since they can be charged by the vehicle's alternator. Higher voltage systems tend to be larger and use less common components.

For this next version I opted for a semi-portable system using 8 cells. This would (hopefully) provide sufficient power in terms of intensity and duration to be truly useful.

This Instructable primarily shows how I put it together. Most of the principles are discussed in my previous two LiFePO4 battery projects, and many of the supplies are the same.

The biggest differences between this and the previous solar generator are the cells and the inverter:

I used eight 305Ah LiFePO4 cells instead of 4 x 104Ah cells, yielding six times the capacity. I checked the cells with a volt meter and they read the same to 1/100th of a volt.

For the inverter I selected a 4000W 24-volt inverter/charger from Sungold Power. This is neither cheap, nor light, however I wanted a relatively bullet-proof system to which I could add another 24-volt battery bank if I wanted to. This inverter includes a 50A charger which allows for charging the batteries when the solar panels aren't providing what you need, and you have access to "shore" power. The reviews were stellar, complaining only about weight and cost. Naturally, I just had to open it up. You can see the transformer and massive heat sinks.

The main external connectors are red to match the recommended color designations from Andersen. This prevents anyone from plugging the 12-volt charger or inverter into the 24-volt system.

A detailed list of parts, prices and sources is in the attached PDF.

I used 3/4-inch (actually 18mm) some Baltic birch plywood for the main case. Since just the cells weigh almost 100 pounds, it would have to be sturdy, with comfortable handles. The cells are compressed using threaded rods covered with plastic tubing. Cardboard spacers protect the cells from each other. You may notice a gap in the spacer between the 4th and 5th cell, this is for a temperature probe from the batter management system (BMS). I kept the terminals covered with tape to prevent errant hardware and tools from shorting across any terminals.

There are several levels of wiring and electronics. The first level connects the batteries in series, and attaches the BMS cell monitoring and balancing leads. The main power leads and BMS connection are threaded through the cell cover.

The cover over the cells mounts the main controls and connections. Referring to the picture, starting from the left and going clockwise

1. Red Andersen Power Pole (APP) SB175 connector to inverter
2. Positive (red) bus bar
3. Negative bus bar
4. 400 Amp power sampler
5. Battery management system
6. Voltage and current meter
7. 12-volt distribution box with fuses
8. 24 to 12 volt 30 Amp converter
9. Main circuit breaker and power switch
10. There are some cables that lead to the top level of the system:
11. APP SB50 connector to solar charge controller
12. Power lead to voltage and current meter
13. Power lead to USB charger
14. Power lead to APP PP15/30/45 connections

The top cover mounts the MPPT Solar Charge Controller, circuit breakers to solar panels, the power meter display and outlets for USB charging and 12 volt devices.There is a second circuit breaker and room to mount a second charge controller for connection to a second bank of solar panels.

At this point the battery system weighs 142 pounds (64.5 Kg).

And here it is. The battery system is connected to solar panels. I added a logger I designed. It records several parameters every few minutes and displays some key information. I did upgrade my solar tracker to four panels and added wheels. The panels are advertised as 200 Watt, however I got between 500 and 600 watts from the four panels for six hours during later summer in Oregon. Even in the winter, with overcast skies I can still squeeze out a few tens of watts to keep the batteries trickle-charged.

I tested the power delivery by plugging in a 1500 watt space heater I set outside so I could run down the battery and go through multiple charge/discharge cycles to collect stats with my logger. The power cable on the heater got warmer than any of the wires on the battery or inverter. I could barely hear the inverter and the fan rarely came on at low power. In contrast the fan on the BougeRV 12V 2000W inverter came on constantly and at high power.

The Data Logger

The BMS, Power Monitor and Victron solar charge controller all have Bluetooth interfaces that allow you to configure and monitor the systems. That's not very convenient when you just want a quick summary of whats happening: Is the system charging or discharging? How much? What is the current capacity? How much is each bank of panels producing? What is happening over time?

I designed software that receives the data stream from one or more Victron devices and the Juntek power monitor. This runs on an Adafruit Feather Express M0 with data logger add-on, and records various settings every few minutes for later analysis. It displays key stats on a display. This will be the subject of a future Instructable. If anyone is interested in the details, let me know. Early versions of the project are on Github.

Was this project worth it?

Isn't it interesting how email spam and proffered YouTube videos seem to mirror your Internet searches? While I was working on these battery projects I got some (unsolicited) information from Ecoflow. They sell a variety of solar-powered products, one of which is the Delta Pro 3. It's advertised as a home backup power system, and includes a mains-powered charger and solar charge controller you can connect directly to some solar panels. It is very similar to what this project does. It costs $3199 (Amazon, February 2025) and has a capacity of 4096 Wh.

The total parts cost for my system is $2430 and has a capacity of 7320 Wh.

(Grin!)

Happy building.

I never planned on mounting the solar tracker permanently, so I had to come up with a semi-portable base. Since the panel mounts were made from unistrut-style channel, I thought I'd try making it from the heavier gauge version. The local home improvement store was the source for 10-foot long pieces of 12-guage channel at about $35 each. I got 2, and chopped off several short pieces to use as spacers. One-half inch galvanized bolts, nuts and washers would hold the pieces together. I started out without wheels and found the base to be very sturdy. The tracker frame holding the panels had more flex than the base.

The whole assemble is heavy and difficult to move so I added wheels. At first I added a single caster to the end of each channel, but because of the way casters work they are frequently off center and the channel twisted. So, I made double-caster assembles using some left-over plastic decking planks. This worked great and I can now easily roll the assemble around on my deck. This allows the whole system to easily be stored in a barn or shed and rolled out as necessary. The caster locks kept it in place during wind.

A close-up of the sensor shows a 3D-Printed mounting I made to replace the original (flimsy) one. It slides into the channel and has a bolt on the bottom to hold it in place. Be sure to follow the instructions carefully for orienting the sensor correctly.