Howdy. I know there are a bunch of posts related to this, but I’ve seen conflicting information based on the latest firmware releases and am hoping for a definitive answer for what’s current.
It’s expensive and a pain to source decent 18650s here in Canada. Huge usb batterypacks are easy and cheap.
All our nodes will be in is_router=true mode and fixed locations. I’m hoping we can just wire in a large external battery and a solar panel, and leave the internal battery slot empty.
I saw some references to router mode actually using power management even if it is plugged into the 5v usb connection. (because it assumes it is autonomous and probably running on solar)
I just want to confirm that it will also do that if the 18650 slot is empty.
I would recommend having an 18650 installed as it nice to see the battery dropping remotely incase the power supply is interrupted. I use this method determining when to go change the battery on my nodes before a complete failure happens. pro tip, most of the usb battery packs have 6 or more 18650’s inside. Just crack one open and desolder the batteries.
I have the standard tbeam that come with meshtastic installed.T-Beam V1.1 ESP32 NEO 6M
Ok, so I learned a lot this weekend. My cousin is a battery/solar expert with a garage full of 18650s reclaimed from cars/bikes etc.
He highly suggested just making an array of the 18650s wired in direct to the internal battery terminals. So we did that.
He also said, a big downside of using the usb interface, is that efficiency is lost with the jumps in voltage that will be required.
I also learned how quickly bluetooth is disabled for is_router nodes. so they truly can only be for nodes that won’t have anyone bluetooth connecting to them. Intermediary nodes only. (or so it seems from testing)
Could you all elaborate on that a little more? I understand there is inefficiency in my personal setup stepping down a 36v scooter battery to 5v. But is there further inefficiency that my 5 volts goes into the usb port? I was under the impression the 18650 just kicks in when my main battery dies.
Battery in USB bank (~3 to 4v) Upconvert to usb 5v >>> tbeam down convert to ~3.3
Each step is usually 80% efficient.
Another aspect is the max discharge voltage of the different power regulators. If the power management is directly interfaced with a battery with no built in management it can change the min and max voltages within the limits of the rest of the components. The device cpu, the radio, etc, require a min voltage, some times as low as 2.1v and is much lower than a state of discharge for li-ion chemistries. All that means is you could technically charge and discharge the batteries more than is usually recommended. Running just at the limits, but with no margin for manfactuing tolerances / safety factor.
My cousin explained it well, though i don’t remember the details. He said there is a large loss by using the usb interface as the voltage needs to adjust a few times, which also creates emf that can affect the antenna.
So last night we stayed up late disassembling ebike batteries to reclaim all their 18650s, then wired them all into 30,000mAh packs complete with a fuse for good measure. Those paperweights were then soldered onto the battery terminals via a plug. We’re hoping to get a month out of them based on testing of actual watt hours. Really depends on how chatty end users are.
Just be careful connecting a bunch of batteries like that. If the difference in voltages are too big the amount of energy that transfers from the high to low voltage cells can be enough to damage the connecting wires, over heat cells, and so on.
Thanks for that warning. I’ve had to trust my cousin on it. He tested the output voltage and charged them so they would be balanced. The first couple times we use them will be outside on concrete incase they explode.