Portable/emergency solar power station. Stats: 120W (95? max so far) solar, 12V 80Ah AGM battery, MPPT solar charge controller, 400W inverter (uses 0.8 A when on), 3 cooling fans (in/out and duct, uses 0.2 A when on, button activated), 6.2 kg/14 lb. case - weighed when holding everything but the panels and battery.
The MPPT effect is quite noticable. On a benchmark test I used a 20V 4.25A power supply to simulate an ~85W panel. I saw 6.8 amps going into the battery at 14.4V (so 98W?). This effect allows me to pull 95W off the two 60W panels in series (so 40V and 2-3A has peaked at 6.5A at 14.6V into the battery per the monitor). I have an old Watt meter than I plan to put between the panels and the case to check all this out.
The system has plenty of room for expansion. I'm currently only running 120W, but I could go up to 780W with a second battery and a 24V inverter (and I can add another 270W of panel on the current system with some parallel connections).
Why build this? Honestly, I was looking for a power solution for multi-day time lapse photography in the mountains - which prompted the first panel purchase. Then my wife expressed concerned about a dire apocalyptic tsunami/earthquake/volcano event from reading the news which kind of flipped the project from a lithium USB brick charger to a full on power station (because all I needed was a reason). So this will be used for photography and camping and picnics until the zombie apocalypse. Editing video under a tree off an 8TB hard drive is a treat.
Step 1: Parts
There are hundreds of charge controllers, hundreds of solar panels and hundreds of batteries that can be combined to produce millions of different systems. My parts where chosen considering: Energy/weight ratio, Cost, Size and Expandablity. My goal was a portable system that roughly breaks even (zero or low +amps to battery) when using my laptop and external hard drive (so 85W + 50W + inverter and some loss = 150W?) at full solar power.
Bill of Materials:
- AGM Battery 12V 80Ah $173
- -Update! I have ordered a 4 lb. 20Ah 12V lithium battery to replace the 50 lb. lead acid battery.
- -The 12V lithium (Battery Tender) is supposed to be plug and play replacement for AGM. $220.
- -Wire cutter
- -Wire stripper
- -Wire crimpers
- -Soldering Iron/solder/flux
- -Hand Drill
- -Table Saw
- -Dremel and various tips
- -Hand torch
- -Heat gun/heat shrink
- -Precision pliers
- -Digital Multimeter
- -Hex drivers and socket wrench
I bought used or from surplus when possible, except for the battery and wire was intentionally new.
Step 2: Pre-Fab
Since I do many DIY projects with repurposed and used parts, I like to build parts of the system, test them out, then prep them for final assembly. It's extra work, but it gives me more control and flexibility during final assembly when the used/surplus parts may have to change between initial design and final assembly.
- Test your parts (use a digital multi-meter, mostly testing for shorts and opens)
- Leave a little extra line in your Pre-Fab connections. In fact - it's a good idea to Pre-Fab and Layout completed sections as you go to get a feel for how long connections need to be.
- Assemble Connections - Panel
- The panel power-out wires (for the "18 V") seem to me to be pretty thin for carrying up to 3.3A, so I took one cable (one comes with each panel), cut it in half, then re-terminated with "Deans" T-plugs (common in the hobby world for high amp applications). All other high power wire-to-wire connections are then T-plugs and 12AWG or similar with the exception of the battery harness.
- During my previous attempts, I burned up a panel, so I install blocking and bypass diodes in all my power sources now. The surplus diodes I got cheap (6TQ045 - 6A 45V Schottky Rectifier) and I have new ones (10SQ045) and I plan to use those moving forward. One fun note about the "surface mount" 6TQ045 is that I could mount it back to back (see picture) for a compact block/bypass diode set.
- The series Y-harness (and parallel Y harness on the load side) were bought new (hobby shop) to save me some work.
- The wire goes from soft to stiff 12 AWG before going into the case. I'm considering changing that as the stiff wire is rubbing on the sharp edges of the CC and putting stress on the T-plugs.
- Test connections, assemble, then retest. Expect ~40 V off the panels (no load)
- The main interconnections inside the case are stiff 12 AWG from home depot and crimp-ring terminals. I soldered every wire-connector connection, including the crimped terminals and solder-coated bare wire inserted into the compression terminals in the charge controller, Watt meter and Volt meter (so just about everything that doesn't have a turning screw).
- The main power terminal 10-circuit block is more important for physical strength and wire management than for conductivity. I did not want to put stress on any of the component connections.
- Even though the charge controller is supposed to take care of everything, all grounds are connected on the terminal block. I made several double connections - a screw through two ring connectors - ensuring ring connections are back to back when I did this. This is how I joined the grounds and connected the battery volt meter.
- The 6 block-to-controller connectors were deliberately bent 90 degrees to compress space during case construction. In the intermediate layout assembly they were flat.
- The connections into the controller are compression screws onto bare (or soldered) wire.
- Test connections, assemble, then retest. All the grounds should be connected.
- I had the battery harness from a battery wall "smart" charger and re-terminated that with ring connectors for this system. It comes with a nice quick disconnect with rubber caps and I don't have to mess with the tensioned battery terminals (or carry those tools).
- I put in a 30 amp fuse into the positive side.
- I put in small ~18AWG leads to the volt meter (which had to be calibrated)
- Test connections, assemble, then retest. A known power source helps (like an 11.1 V LiPo is nice), but do not hook up panels while testing the battery side with a non-lead acid battery.
- In my setup, the Watt meter is the first stop in the load side. My Watt meter came without terminals. I have stiff wire coming out of the block which then transitions to the soft 8 AWG at the Watt meter source junction.
- The out port of the Watt meter goes to the parallel harness which splits - one side goes to the inverter (another soft-hard wire junction) and the other side powers the fans in the case.
- The inverter connection is a carefully measured set of stiff wires to minimize stress on the T-plugs. The terminal ring connectors are crimped to naturally lay flat on the inverter screw posts before tightening the thumb screws.
- The only way I know to tap power to reduce amps without burning them off as heat is a switching regulator. The auxiliary power line off the parallel harness goes to a 12V 350 mA switching regulator (normally to power 1W LEDs). There is a switch built in to turn the fan system on/off (see mounting later).
- The 12V switching adapter is sandwiched to a pin-out board with three plugs - 2 for the intake/exhaust 12V fans and 1 for another switching adapter (5V ~1A) for getting 5V to the small fan above the CC to duct the heat off the top of the CC. once past the 12V switching adapter I used small wires to make the connections. (There is a switch mounted on the outside of the case that controls the fans.)
- Test connections, assemble, then retest. A known power source helps (like an 11.1 V LiPo is nice), but do not hook up the panels while testing the battery side with a non-lead acid battery.
Step 3: Tips and Tricks (a Mini-Instructable)
This is a list of tricks that made my life easier when building this project.
- The hard insulation on my crimp-type terminals can be worked like reversible heat shrink. Hold the terminal with a pair of pliers, heat the plastic tube with a heat gun until soft. Slide off the tube and position it on the wire like you would heat shrink. Compete crimping and soldering. Reheat the tube and slide back into position for an undamaged and secure insulator.
- If you burn something, cut it off or replace it. Carbon conducts. An exception would be polishing plastic panels - just scrape or buff off any carbon black to avoid potential shorts.
- The diode adapter construction:
- Update -The surface mount diode connectors broke when flexed too many times. I recommend staying with the traditional round connectors or reinforcing the surface mount connections. The electrical testing image is still valid.
- all connections except the diode sandwich are pre tinned (solder coated) before the final joining
- don't forget the heat shrink
- solder both the female plug terminals with correct polarity coloring (red for + and black for -)
- complete the crimping connector on the female red lead so the ring is in the middle of the black lead (or a little toward the female side will make later steps easier), but leave the plastic insulation off the connector for now so you can solder the sandwich without burning the insulation
- clip off the non-contacted pin from the diodes (if necessary)
- flux and sandwich the flat ring terminal between the diodes using an alligator clip
- solder the sandwich junction (You are welcome to put some heat shrink protection on this junction. I initially left it unprotected thinking it would need to be able to cool down.)
- position the female lead crimp connection insulation
- solder the male plug negative terminal using the sandwich technique for the two black wires (You will need larger heat shrink here.)
- solder the male plug positive terminal with a red wire
- trim and tin the red and black leads off the male terminals so they just fit into the elbow of the diode pins
- solder the diode connections (the two connections are equivalent)
Step 4: Layout Assembly
As I mentioned, when dealing with unknown components I like to "breadboard" the component layout. It turns out I was able to simply cut the layout panel for the monitoring devices and mount the whole group into the case directly. One surprise for me was that several items need to be "spaced" from any surfaces. The inverter and Watt meter needed "risers" (thin plastic blocks) to allow air flow behind (i.e. on all sides) of the device. This was a great thing to learn during Layout instead of Case Assembly.
- Get a largish plastic panel (surplus for me). I measured and drilled holes and used 3M screws with Nylon lock-nuts for almost all mounting.
- Mount the Charge Controller.
- Mount the 8-circuit block under the charge controller. My philosophy is to minimize line crossing, so I have most of my positive lines next to my negative lines with spaces between pairs of lines (for grounding jumpers and for adding a second battery later).
- Mount all your monitoring devices together (or as you wish). I had to create some holder plates for my Watt meter and Volt meter. Use plastic posts or plastic standoffs when possible. You may notice my extra Volt meter block. I plan to add a second battery and flip to a 24V battery system in the future. The battery system voltage determines the charge controller limits - 390W for 12V, 780W for 24V. This also allows for generally lower amperage all around. On the down side, this means purchasing a 24V inverter if you don't already have one.
- Mount your inverter.
- Review all parts for air flow and stress-free connections.
- Organize and make your connections.
- Test connections, assemble, then retest.
Step 5: Case Assembly
Consider your layout and guesstimate the size of the case you need. Then try to compress a little more, but ensure proper air flow. Consider if you want your panels (if they fold) inside the case as well. Some people put their AGM batteries in their case as well. Make sure you have room for all your cables and "extras" inside the case.
- Undo all connections. Don't fight/damage wires while building the case.
- Remount the Charge Controller and then remove it (seriously). If you can easily add the other components with the charge controller in place, consider a smaller case (unless you're adding panels and batteries into the case...)
- Mount the 8-circuit block to align with the CC terminals.
- Mount the monitoring panels
- Mount the inverter. One interesting note is that I tilted the inverter on a ramp to be flush with the sloping wall of the case.
- Mount the fans - I did an intake fan, and exhaust (out) fan and a fan above the CC to meet the manufacturers recommendation.
- Figure out where your wire in/out ports need to be and make those. The lid of my surplus case happens to be double walled. This was a pain when mounting the fans and screen covers (I put spacers in between the walls to keep from deforming the lid), but it worked out great for adding a sliding panel inside the lid to seal the large battery port. The port is large because the initial connections were battery clamps instead of a quick connect.
- Wire everything except the CC.
- Re-install the CC and make those 6 connections.
- Test connections before powering up.
Step 6: Bells and Whistles
There's really no end to what can be done with this system.
- Labeling: Since this was built for the family I added some labels with the help of a friend with a laser cutter powerful enough to cut card stock. He made me some nifty stencils that kind of worked with spray paint. The case ports "TO PANEL" and "TO BATTERY" are labeled and I labeled the case "SOLAR PROJECT". I plan to add a laminated card with basic instructions.
- I purchased the system monitor for the Charge Controller. I really like being able to see the status of everything going on. The system monitor makes the Watt meter and single Volt meter redundant, but I like having them both. And I'll need the two Volt meters when I get two batteries to keep an eye on charge balance. Mounting all the displays in the case wall would probably have saved space, but I tend to be rough on my gear, so the delicate screens are inside while the system monitor has a remote cable.
- There is a switch on top of the case to turn the fans on/off. This saves 0.2 A when not needed, and I can watch the system monitor for Charge Controller temperature. I plan to use the case in hot weather. Other cases have switches for everything and can be internally lit (think car light systems). I do plan to add LED lights around the inside of my case.
- The battery is in a box with handles for easier carrying and allows terminal connections with the box lid in place. It's still a very heavy battery and the main limiter on portability.
- Other system-in-a-case have waterproof ports (such as wall mounted gasket SAE plugs with rubber caps, 12V car plugs with rubber caps, etc.), external 12V terminals for battery-in-case systems, and many other features. Search online for ideas.
- See field notes for more additions for this system.
Step 7: Field Notes
A few things I've learned while using the system.
- I already knew that the battery and charge system should really not be in the sun (hence the fans). At first I used a thin panel to shade the case and battery.
- But sitting in the sun yourself is not fun and it's hard to see computer screens, etc. I've added a 30 foot high quality copper extension cord between the panels and the case so I can sit in the shade (or in the car) while the panels are far enough away from shade to get sun for a few hours before I have to move them to a better location.
- The inverter stores power. To quench the inverter before maintenance, unplug the battery and panels. Switch the inverter "on" for a few seconds without power supplied. This will use up the stored power in the inverter and make it safer to work around.
- The surface mount panel diodes broke under stress. I chose to replace them with the traditional round diodes instead of reinforcing the surface mount diode connections.
- There are 12V lithium batteries that are designed to be a simple swap for AGM lead-acid batteries (charge the same, etc.) as long as your charge system doesn't have a "desulfinate" step. I have ordered a 4 lb. 20Ah 12V to replace the 50 lb. 80Ah 12V lead-acid for about the same price. I'll keep you posted on the results. (I plan to leave the lead-acid at home.)
Be safe and have fun!
P.S. This is my first Instructable. I think I have most of the pictures labeled. Feedback is welcome!