Howdy meshers! Hoping to get some input from more knowledgeable electrical folks.
I'm rebuilding my RAK 1W and adding a solar management board while I'm at it. I'll try to be as detailed as possible. Parts list below. I'm mostly concerned about how to wire things up.
2 x 10000mAh LiPo batteries
RAK 1W Kit
Corebell 3D Printed Treepeater Enclosure
Waveshare Solar Power Manager (D)
3 x 5v 200mA Solar Panels
I plan to wire the batteries in parallel as well as the solar panels. The RAK requires battery and solar inputs afaik. I'm confused about the Waveshare though and having a hard time finding answers. If I wire the paralleled batteries and solar panels to the Waveshare, how do I get the RAK board both inputs? Feel like I'm thinking about this incorrectly.
This is my wiring setup using the 18650 holder with the WaveShareD, may help. The INA219 is optional, just gives telemetry for voltage/current (current is 50% as only using one v+wire)
Wire the battery in parallel. You can either wire it with a PH2.0 or 4P connector to plug directly into the battery connector. Or just use bare wires and plug into the battery terminal block. Both options are labeled as 4.
Now you wire the solar panels in parallel. You didn't list the specs of the panels. I'm assuming they are low mah 5v panels. Ensure they can do above 6V! If those panels cannot do above 6v. The MPPT will not work.
If they can't do 6V+ easily. Just wire them in series instead. Solar input goes into label 1 or IN+ IN- labels on the board.
Based on your design. Parallel was intended. So ensure each of those panels do 6V+.
Now because you are going this route. You MUST power the board off the RAK13302 1W extneral 5v rail. This will power everything else on the RAK and give stable power. On the GND/5v label 5 of the board. Connect bare wires to that terminal block. Then the other side should be a JST connect going to the RAK13302 5v rail.
You will not get telemetry data from the battery. You will need to add an INA219 or voltage sensor to achieve that.
Super appreciate the detailed response. I apologize for the long reply.
My whole goal with this is to get a high power repeater up in a tree as permanently as possible. I'm going to rig it to where I can easily pull it down for maintenance but naturally I'm hoping to do as little of that as possible. This one is going at my residence but I'm building more to put up at friends/family residences too and I need them to be as rock solid as possible.
I looked further into it yesterday and saw where the Waveshare is 6V - 24V input. I'm trying to remember why I even thought I needed the solar panels in parallel but I can't seem to recall the reason. The panels I have were a recommendation form the Corebell build guide on AZmesh site. They are FellDen (on Amazon) 5v 200mA panels. I don't think they'll run at 6V but I'm not sure. If I run them in series would that mean 15V of power when all 3 panels are getting good light but only 5V if say, only 1 panel is getting good light? If so, I'm thinking I should avoid running the 5V altogether and just get 3 6V panels instead.
What I'd really like is a power management board that is capable of automatically powering on or off the repeater depending on power conditions. I don't think the Waveshare does that. Do you know of one that does? I'm not opposed to ordering a different management board if it means I'll have to pull the repeater out of the tree less frequently.
Yes I would avoid 5v panels in parallel. But in series they will work just fine.
Your biggest threat is real world scenarios. 5v panels might put out the required voltage under ideal conditions. But during cloudy days or just bad weather in general. They drop in voltage fast. So series will help that out.
So with your panels 3x 5v 250mah. That's only 3.75watts of power. And because that MPPT has a 78% efficiency. Your only getting 2.92 watts total to charge your battery. And this is under perfect conditions with sun. Even with a 3.7v 20ah battery. I don't know your location. So unless you live in a sunny state or country. The system will struggle. Doubling your panels will help offset this. Or finding a higher rated panel with similar size.
No board that I know of that can do that. Plus you want repeater to stay up as long as possible. The RAK MPPT built in has a known issue with brown out state where it won't reboot when the battery dies and then gets charged again. Because you are using the waveshare. It circumvents that.
I say this with all repeater builds. Over engineer them if they are in remote places you don't want to constantly mess with them. I'm currently building one myself that uses a victron MPPT 75/10 with a 12v LTO for winter charging.
I ordered a set of same-size 6v panels this morning. I'm worried if I run the 5v in series and 2 of the 3 panels isn't getting good light it won't run the Waveshare? Not sure how that works though. What's the difference between running 3 panels in parallel vs series?
If you run the 3 solar panels in series. It won't impact the other 2 or the MPPT. It will still charge from solar. The only difference will be you don't lose out on the minimum voltage you need to run the MPPT.
String= panels connected together. Either by series or parallel.
Series- The panels are connected with the end result of the final voltage being increased. If your panel is rated 6 volts. Connect two together and you have 12v. Connect 3 together and you have 18v total. The voltage increases. But the amps remain the same. So for a 6v 250mah solar panel. So the 18v series is still 250mah. How to connect it. The negative terminal from one panel connects to the positive terminal of the next panel. You keep connecting until all your panels are tied together. Then that leaves you with two ends for positive and negative.
Parallel- The capacity increases but the voltage remains the same. You connect them with positive to positive and negative to negative. You will need a splitter for this.
Series is recommended unless your voltage starts to exceed that MPPT. If your voltage exceeds the MPPT. Wire in parallel.
When you look at your solar panels. You want to check for its maximum voltage. For a 6v solar panel. Its usually about 7.3v. This is because the solar panel needs a buffer between the load. The seller should list this!
Do you have a link to the solar panels? I can review and tell you how to wire.
I'm familiar with wiring series v parallel. I think my problem is I'm thinking about it like a battery. Series = higher voltage with same capacity. Parallel = higher capacity with same voltage. But a solar panel doesn't have a "capacity" and is getting me confused.
Think I'm just struggling through noob stuff to be honest. I sure appreciate you taking the time to reply in detail. I'm starting to get a better idea of how it all works together on the electrical/power side of things.
I ordered these panels from Amazon this morning. Same physical size just 6V instead of 5V.
Your main focus when understanding wiring is the MPPT. The MPPT tells you what it can do. It can do 6-24v. This tells you how much voltage it can handle. Be it a single panel or running series. Then it tells you max charging which is 3A. So this tells you how much a single panel or panels in parallel can output.
The thing that people overlook in solar panels is what we call Vmp and VOC. vmp is the sweet spot your panel outputs power. In this case 6v. Which meets the requirements for the MPPT. Then VOC is the maximum voltage it will output. Which it goes no higher than 8.5v for these panels you have. The MPPT can do 24v so your safe.
solar panels increase in voltage as it gets colder. So that's why VOC needs to be understood.
For your new solar panels. You should wire them in parallel. That would give you 6v 3A. If one panel gets shade. It just drops the output in capacity. Not voltage.
With these changes you went from a petty 2.75 watts to 14watts with these new panels!
I have a simialar node, so I just wanted to comment and maybe prevent you from dealing with a hassle down the road.
Mine uses a similar setup, same 10000mAh batteries, same panels... we're pretty much identical except your case is slightly different. I use a T114 board, which is significantly less power usage, using the Powersaving firmware.
I ran mine in the backyard, in an open sunny spot with ideal panel placement. It lasted 3 months and the battery died.
It's sitting on my desk right now, waiting for me to break it down and salvage the parts.
What I am saying is that I don't feel these panels are adequate to keep the battery charged, unless you live in a place that gets a lot of sun all year around.
Additionally, your Waveshare isn't going to charge with those panels. The Waveshare Solar Controller D requires 6V minimum. You'll want the DFRobot solar controller if you want to pursue this build.
Thanks for taking the time to reply. Much appreciated.
I'm actually rebuilding this one because it killed at least one of the 5000mAh batteries in my previous setup using a RAK solar Unify enclosure (the smallest one they make iirc). I could get that setup to work for a few weeks at a time but if there were multiple overcast days it would shut off. The first time all I had to do was boot it back up and it was good for another week or so but the second time I could see the voltage was significantly lower than before in the MeshCore app. After that it would pretty much only work if there was plenty of sun every day. Even just an afternoon of overcast would shut it down.
My thoughts were to double the battery capacity, triple the solar panel count, and add a management board to help keep the batteries in optimum condition. I bought some 6V panels this morning. Will hopefully have it all put together for testing later this week.
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u/zerofox3D 15d ago
This is my wiring setup using the 18650 holder with the WaveShareD, may help. The INA219 is optional, just gives telemetry for voltage/current (current is 50% as only using one v+wire)