Been making rapid progress on my muon cell/lorawan devices in m1e's with the large battery inside. The usecase is a LRW gateway up on the side of a mountain with solar and cell link to TTN. Works mostly but needs beefier batteries in the cold...
So I have made 3 muon/m1e devices that link cell and lorawan when they can one of the other (favoring lorawan) and do things like disable the LED's because I dont want those blinking in the middle of the woods at night, but I can reenable them etc... I have them measuring AQI and basic weather data on the side of 3 mountains (or will, they will replace dragino sensors). Testing so far is going very well. I have them placed around my house to just see how they all work before moving them where they are much harder to get to. The gps works awesome, self setting location and elevation!
But one thing I am stuck on: solar power. Reading the various questions about this, seemed like a good time to ask people what they ended up doing.
My other sensors have panels with battery chargers connected to lifepo4 batteries in boxes, etc... that just took time to build and add to the bulk and annoyance hauling these all up mountains and finding place to place this all in trees and such. I was hoping for something simpler with these m1e's and their larger built in batteries.
It seems like I have to basically keep these battery boxes but move from panel > battery > 12v > buck converter to 5v > device (borons right now) and go with something like panel > battery > 12 to PD USB-C that supports 9v > usb c on muon.
There are things like the df robot all in one system but they only put out 1A at 12V. The muon sips in pushing 2A when it is doing all the radio work. All my math says this df robot 1A system will be marginal under normal use.
I'm concerned about just a panel that might overshoot 12v and hurt the muon if I connect it directly to the board even though it says 6-12V.
I'd love something simple and inline, like panel/manager/battery putting out solid 9-12V >> plug >> muon but seems like this might not exist. I chose lifepo4 because it will be better able to handle sitting outside in the winter.
So! how have people make this work, would love exact parts and such, if you are open to sharing!
You can connect a 12V solar panel the Muon VIN screw terminals. It's connected to the bq24195 PMIC, and that has an absolute maximum rating of 17V, so being a few volts over will not damage it.
Depending on the size of the panel you may need to adjust the input current limit in the power manager. If you discover that charging turns on and off continuously when solar powered, what is likely happening is that the input current limit is too high for the panel, so the voltage collapses under the minimum charge voltage, which causes charging to turn off, the voltage recovers, then charging turns on and the cycle repeats. Limiting the current to a size appropriate for the panel prevents this from happening.
I have been operating a number of solar powered river monitoring stations for some years now. Some are in Canada, so see some pretty cold temperatures. Using Borons (and a couple of B-SoM as a temporary fix - looking forward to the Electron 2 becoming availble!)
This is what I have found;
A standard 12V solar panel could have an open-circuit voltage over 21V in bright sunshine. I have been using a shunt regulator to drop this down a bit; bonus is that it dissipates some power in my enclosure and helps to warm the batteries!
Even though they are not specified for cold weather use, standard Li-polymer have been working OK, but their charging and self-discharge rates are much worse in cold temperatures.
I haven’t found an off-the shelf power management IC for anything other than Li-polymer, or Lead-acid. There nust be something out there, I just haven’t found it in a form suitable for the small cells that would be needed.
I have some Sodium-ion cells on order, and am looking forward to seeing if these are going to be better at low temperatures.
@Gwyn My use case is similar! What I have arrived at is
Solar Panel > charge manager > 12v battery > automotive 12v to PD usb charger that can put out more than 5V > usb c > muon
and
Solar Panel > charge manager > 12v battery > automotive usb-a 5v buck > usb > boron
I have to admit I am really disappointed in this, it is a lot of extra gear, and I was hoping that a panel into the muon directly would work. It is a bit sad because the muon is starting to prove less and less valuable as its limitations come into focus, it has half implemented Wire1, it has serious bugs in the HAL, addressing issues on i2c, and the variable input of voltage is far less useful than I hoped. The only reason I continue with the muon is that 1 I bought them, 2 the case is really useful, and 3 hoping some of these limitations and defects are addressed 4 eventually sat connectivity to go even more remote into the woods.
But again with all the extra "stuff" needed the value of the m1e is lowering because if I need a watertight project box to hold all this solar gear, I can just stuff the muon in there already...
@Gwyn can you share some more specifics of your design, because it sound like I am mimic it and get closer to what I want. I am use LiFePo4 because it rarely gets below about 25F here, and so far they are working, but your setup sounds vastly less messy than mine and I'd love to simplify...I really wanted something I can put in my backpack and haul into the woods vs. all the junk I am hauling now.