I’m in the process of constructing some solar nodes for my community but am very concerned about which batteries would be safe to use.
It doesn’t take more than a few mouse clicks to find all sorts of horror stories about lithium batteries catching fire and/or exploding and the last thing I want to do is make a node that is going to potentially cause harm.
I’m using Wisblock Raks, “5v” solar panels (realistically I’ve seen them up to 7v so I put a buck converter on them to make sure it stays at 5.1 volts or less), and I’m currently using MakerFocus 10000mAh batteries (figuring for long winter, dark days).
I know the MakerFocus has the protection circuits built in which should prevent overcharge, undercharge, and charing/discharging too fast (which I think would protect against any unexpected shorts).
In my area, the most extreme temps I’ve seen were -5 to 110 (F).
For enclosures, I’m using the typical ABS enclosures on Amazon and also some of the small black Apache cases from Harbor Freight.
Right now, I’m in paralysis of deploying my nodes because I’m deeply paranoid about something happening to the batteries and causing a fire or something.
Would some 18650s with BMS be a better option? I’m 100% only worried about safety.
What can I do to guarantee nothing bad will happen to the batteries I’m utilizing and also what ideas would you have to potentially contain any fires/explosions in your solar nodes?
I am totally with your worry. I have one on the roof of my employer and if that burns down the building, it might cause some trouble. In my case the surface underneath the node location is a flat roof with concrete slabs and absolutely no foliage or the like around it being to top of a very tall building - there is absolutely nothing to catch fire if my batteries burn and fall out of the plastic enclosure, and the location already has lightning strike protection.
In the image the node box is marked with a red dot. (The image background is altered.)
Lucky. (My next build will be a metal case.) I would definitely put the batteries into their own metal case and fixed to metal or with a metal “catching” device under the mounting. Some use sand in the box to prevent the heat from transferring to the box.
A layer of metal foil insulation over plastic spacers as shown here (Solar node for top of tall building using the Waveshare D solar power manager) with a north facing node box in shadow behind the south facing solar panel and behind the south facing mounting plate (see image above) results in a node temperature of only a couple of Celcius degrees above ambient.
In all honesty I would never take responsibility for placing a device in or on a residential building because the tiny chances of a catastrophic failure are not the issue: you just do not want the responsibility and want to be able to sleep at night. So I am aiming to build a node that I could “leave in my child’s bedroom” so to speak, and let people know the parts for it. Putting it up in someone else’s residential property is out of the question - they would have to do that themselves.
I even relegate my self-built node arrangements with batteries and not running on mains (even if they use consumer electronics) to the garden tree (Solar 24/7 store & forward pole node using off-the-shelf components: test) or my car (Car node with external antenna) as they can burn to their heart’s content, and for lightning strike reasons. I do not even want a node on my chimney without a lightning conductor as this invites stress if lightning should strike (I live somewhere where lightning happens nearly every evening in summer) and is has not proven possible to find any company willing to take on such a small job.
So I would say:
Thermal management of the charging process when cold and discharging process when hot.
Metal boxing and fire-proof fixing, or catching, of at least the battery/ies.
Put it somewhere where the fire could not cause any harm to people: lamp posts, trees, churches, water towers, places with extant lightning strike protection if your node is the highest part of the building etc. etc.
Oh wow. I’m glad it’s not just me who is highly concerned about this sort of thing. I’m seeing tons of posts on Reddit and other places of folks just putting up solar nodes seemingly willy-nilly without any concern of something happening to the battery.
I suppose the smaller the battery, the lower the risk factor. Even still, the risk factor will still be present.
The only thing I would remotely feel comfortable deploying would be one of those Harbor Breeze solar lights from Lowes moded to house the smaller Wisblock Rak to where the only interaction to the battery is soldering the JST pigtail to the tab folds of the 18650 holder. (Garden Light Turned Mesh Network Node | Hackaday) You gotta think millions of those are sold and folks just trustingly place them in their yards. And I wouldn’t imagine 1 single 1500 mAh 18650 battery could burn for long enough to do any damage.
I thought about some sort of metal enclosure for the battery so if it were to catch fire, it would be fairly well contained. Even then, I’d still be highly concerned. Would the metal hold up to the heat of burning lithium? Would there be flaming debris that could possibly light up some dry fallen leaf somewhere?
I live in a rural area with lots of woods which is where I ideally wanted to place two separate nodes due to the elevation. I’ve given thought to buying solar panels with built in batteries like hunters use for their trail cams. Most of them have USB power outputs so I’ve thought about just doing it that way but frankly God only knows what QC and safety precautions those have had, particularly the no-name brands from China.
This totally sucks. I’m with you, though. I don’t even think I’d want to build a node for someone. Too much liability. I’ll probably just use my parts to build a nice on-grid home node and give away the batteries.
Well I would not be so negative. I realise now that the issue is not burning down a forest. There must be a build that is fire proof. Has to be. Just needs work and time and more expense.
Flaming debris and leaves could be dealt with by sand in the box. You can even test it burning and make a cool video - though not sure how to make it catch fire.
I will not give up my quest, it just means a lot more steps in the process. One day someone will manufacture such a ready-made node with all the safety certificates, 100% guaranteed. It would be sold as “Mestastic solar node for petrol refinery” or similar… lol.
And there are LiFePo4 batteries such as the Jackery Explorer 100 Plus, which are completely and utterly harmless regarding fire. I had a different 100 Ah LiFePo4 running in the house without any worries - and the existence of these batteries is what allowed me to step into DIY solar power without having to worry about the fire risk to my home. This is one reason I use them in my builds if I can.
The Jackery Explorer 100 Plus LiFePo4 battery is magnificent and runs a 0.1 mA node for about 9 days and the RAK 5 times longer than that. Unlike other batteries in Europe, it does not automatically switch off at the currents drawn by Meshtastic nodes. A really good piece of kit. BUT there is a problem with the USB C input from the solar panel which I thoight I might have solved but did not (no thanks to Jackery technical dept) (see section “Testing using USB C input via USB A output from panel to prevent drain of battery by the solar panel” in this post Solar 24/7 store & forward pole node using off-the-shelf components: test); and not sure it works for smaller non-Jackery panels, so it would have to be a “proper build” that is not a hidden construct.
I think the aim of making it cheap and safe is unlikely to be realised, but making it safe enough to sleep at night is possible.
I’ve been taking what you said to heart and have come across a few possible solutions.
There’s a company out of the Netherlands called “LithiumSafe” which makes bags that can withstand a battery explosion and safely vent while filtering out the toxic fumes and preventing flame from escaping. Looks pretty promising. Lithium battery safety bag – LithiumSafe
I wish there was a LiFePo4 battery that could perfectly mimic the typical 3.7 LiPos that we’re both concerned about. I have several “Solar Generators” that are LiFePo4 and I know those are safe. I just wish there was a hand-sized version meant for solar charging.
The Wisblock Rak can run on 3.2v. The LiFePo4 drain cycle for the small cells is 3.6 - 3.0v so theoretically a handful of 14500 batteries and a cheap USB charger could be utilized to facilitate a safe solar node.
I have given up predicting what is a good idea. You would have to ask a trusted expert. I have a friend who is solar crazy and whose brother in an electrician… I run my ideas past him but cannoat advise myself.
The radio controlled world has various bags/pouches/boxes available to help reduce fire risks. You could either just buy something to protect the batteries or something larger that your entire node would fit in.
I bought one of these from AliExpress Fireproof and Waterproof High Quality RC LiPo Battery Safety Bag Safe Guard Charge Sack 18x23cm 30x23cm Red Black Silver https://a.aliexpress.com/_Euze637 for storing batteries in when not in use. Pretty cheap and looks ok, guess I won’t know how well it works unless something goes wrong though…
Forgot to mention. This channel has loads of tree nodes Swiss Meshtastic User . I have lived in, and worked in science in Switzerland, and if they are prepared to do it, it must be ok, because the place is so strait-laced and tech savy and deeply law abiding that I would do what they do.
so only protected LiIon cells should ever ever be used as the protection circuit prevents any over charging.
I think any metal casing of a Li battery needs to be extremely extremely robust to withstand the explosions shown. The LiPo batteries produce a plasma flame, and the LiIon simply explode like a bomb.
The video shows that LiFePo4 is by far and away the safer battery, as used in the Jackery Explorer 100 Plus
I’ve built a node with two 18650 LTO batteries. Questions welcome. Works great. The only trouble was finding a solar panel that worked decently, but that was solved. 12v “feeder” panel worked great (sold as 6v but actually output 12v)
The 2 batteries weren’t that much more than regular lithium ion. They’ll supposedly take tons of charge cycles, too, so will probably outlast me lol.
Tldr I’d consider LTO batteries if safety is a concern.
I’ve been in contact with the guy that makes the mppt controller for LTOs for meshtastic and he shares my concern.
I can get a basic LTO cell for about 15 bucks per cell, my concern is charging it via solar. 2.4v is nominal and between 2.6v and 2.8v is the charge cutoff level. I cannot find a charge controller that will stop charging at 2.8v.
In my mind, a single cell with a boost regulator can get the voltage up to 5v for USB interface so I’m not too worried about that. Granted, I’d rather find a way to boost it only to 4v so I can use the JST battery port instead of the USB port.
I would love to see pictures of your setup, radioid, and a parts list.
Hazarding a guess, you got a 12v LTO pack and are just using a regular solar regular set to lithium instead of SLA with a big solar panel and using a buck converter to bring the voltage down to what the node needs?
The board that’s linked can handle 2.8v charge. He built it specifically to handle these cells, though provides options on the board to select other types.
It’s 2 boards that are connected to each other. Charge control and voltage regulation.
Just using 2 LTO batteries in parallel here, it all works just as it should. They happen to be 18650 size cells. Fit into battery holders. Wired in parallel to the board. They don’t charge past 2.8v.
The boards do buck voltage up a little on output and feeds the RAK about 3.6v (to the jst port). This happens to be right about the threshold that they work fine, and it’s not taking much to up-convert by about 1v.
The board has solar input and has switches that select various input voltage.
My problem when trying a panel that did just under barely a max of 7v was that it wasn’t quite enough to pass decently though the boards. It just wasn’t enough continuous voltage input to trigger his output so I found a higher voltage panel with a seemingly decent current output as well and it’s been great ever since. 12v input but the boards are selectable on input.
Hakadi 18650 cells are what I used. I think it was under $20 for 4 of them. Maybe a bit more with shipping. Only used 2, and plan to put the other 2 to use in another build someday.
That’s really about it for parts. Batteries, the magic boards, the RAK, antenna connector, jst connectors, antenna itself, some glue for the holders, sealant, and the box. Oh, and some standoffs so all 3 boards are one little stack of fun. The RAK"s 4th corner doesn’t perfectly align but 3 of them do.
Great little board. A little extra cost but they work well and there’s no better design for these uses that I know of.
Can send a picture a little later but wanted to comment while I could.
Not sure I have all the parts saved specifically, but here are 2 pics of the inside and one of the outside. There is a breather vent plug and another hole for the solar panel cable to enter the enclosure.
I’m not huge on having the RAK sideways. Have to take the board out if I need to flash via USB if Bluetooth fails. A slim angled USB cable would remedy that, or slim extender to attach to.
Have tried RAK on top vs. bottom, and it doesn’t really matter but it does make it easier to adjust the solar panel input DIP switches and measure voltages with RAK on bottom. It could just as easily be off to the side, or elsewhere if the batteries were somewhere else. The front does have 2 bolts coming in through the front of the case, though. They don’t protrude in far enough to touch the batteries. Yes, the “feeder” solar panel came with the mount.
I’m satisfied enough with the build.
Now that I look at the pics, I think the DIP switch was set for the previous solar panel. Be sure to follow the directions and take measurements of what the panel is capable of.
Man that is a beautiful node and thank you for telling me the specific batteries!
When you’re referring to the “magic boards”, I’m guessing you’re talking about the ones that the guy from Oregon makes and sells on Etsy that are sold out?
I’m going to order some of these batteries pronto.
This design has protections for many failure modes:
Using fuses to prevent a shorting battery from getting all its’ neighbor’s power shunted through it. This is only necessary with more than one battery.
a thermal cutoff cuts the solar circuit when the battery temp exceeds 50c (or whatever temp your battery’s datasheet specifies) and reconnects the solar panel when the temp goes 15c below the cutoff temp. Note that the metal shell is live - but it comes with a little silicone sleeve. https://aliexpress.com/item/32893056909.html
a thermal fuse permanently disconnects the batteries if the temperature exceeds 80c. This is a last ditch effort to prevent thermal runaway - if batteries exceed 80c, the node needs servicing by a human. Note that it’s almost impossible to solder to these things, as they overheat and the fuse blows. If you’re quick, you can solder them, or you can go the easy route and use ferrules and a crimper. https://aliexpress.com/item/4000583221153.html
BMS: obviously @keithmon (Voltaic Enclosures on Etsy) has the best BMS, but for preventing OVERcharging, which is where the danger is, any functioning 1S BMS is sufficient. Keith’s BMS excels at preventing damage due to overDIScharging.
Have your solar panel face south and have your enclosure behind it. The solar panel itself will shade the enclosure, lowering temperatures quite a bit.
Have your node high up and on a narrow pole/branch. At ground level in summer, my solar nodes reached 53c. At 3 meters, they never passed 45c, well within spec. And to be clear, our summers are HOT.
Visit us in #solar-power in the meshtastic discord for more tips.
Your welcome. Yep, the Etsy link has a waiting list. Seems to make a batch and they sell out within a relatively short time.
I’ve been happy with those batteries. Really cool tech. Nice that they fit 18650 battery holders. Soldered in parallel. Stuck 2 together. Soldered jst connector, insert batteries.
One thing I noticed in the earlier pics of the board was my not great soldering on the board, which I did fix later once I got some better gear to work with. Think I also used “2” on the switches for the newer solar panel for 11.x volts.
Be careful with jst connectors that have the wrong polarity. I think a couple of these were backwards but are wired correctly where they connect on the other end.
You can also see in the lower right side how one of the standoffs doesn’t quite match from RAK to the charge boards. Think I ended up adding a small amount of insulation there later. The other 3 line up well to make it all stack like that.
Debating making a handful more of these with a few adjustments.
