Two years now since you posted this about the 18650 vs the 217003 battery. Did/has the 217003 out-performed and out-lasted the 18650 in your T-Beams? I’m looking for batteries right now for a couple of T-Beam v1.1 units that will be arriving soon and ran across this. If the 217003’s can offer 40% longer run-time is there a reason this isn’t the go-to battery for the T-Beam’s??? Also, in your picture it looks like you have a “button-top” 217003 is that correct? In the case of the 217003 does the button-top fit better than the flat top? As we know the flat top of the 18650 is the proper one due to tight fit issues if you use the button-top.
It’s a 21700 (you added a 3). Yes the 15x units I deployed in my geographical area are working well after a few years. No it’s not button top, it’s flat top - probably what you’re seeing as a button is the pressure relief vent (in case fire, it will deflagrate rather than explode). I paried them all with ~4Watt 5V solar panels (Mini Solar Panel 5V 4.2W 840mA Polycrystalline Silicon Portable HIGH QUALITY :-) | eBay) hardwired into the USB power inlet circuit (with another diode). They have never gotten below 15% battery capacity over a day with decent use (messaging, weather reporting, concact closure on a few), and they always charge back up in the winter before dusk. 21700 battery and encapsulated solar panel for scale (spare parts, was going to build 20x, but found that I didn’t need the extra coverage).
As for the reason the 18650s were used, probably because they are/were more comon when the device was designed. The difference between and 65.0 and 70.0 is only is only 5mm (about 1/4" total, so 1/8" additional encroachment on the PCB pads) - close enough. and the diameter of the 21700 is only 3mm more than the original 18650 size.
I did note that the 18650s with a typical work load would not survive the day, which is why I sought other options in roghly the same footprint.
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BTW, don’t cheap out on batteries. Look for LG, Samsung, or Panasonic, from reputable sources. There are a ton more fakes on the market than most people realize. After all, one simply ned to re-heatshrink the cell with a different label… but the discharge curve and capacity doesn’t lie.
DigiKey is solid, I bought my batteries from them and though a slightly tight fit they worked. I did not continue to use the T-Beam’s as I was looking for a product that supported AP use of multiple nodes. perhaps the software has evolved in two years, and my original use case was multiple users attaching to a single T-beam… at the time I could only get a single node to pair with a single T-beam.
It is still one user per node, we increased the max node count so multiple users per node is probably even less likely now.
Absolutely amazing! Thank you for sharing! Can you post more about these outdoor units perhaps? Love the clear photos. I’d like to do the same as you’ve done in your area where I can deploy around 15-20 units to encompass a group of people in my area. Can you show us the box you use to keep it all weather proof and such? And just to clarify are you using the T-Beam v1.1 devices or the RAK route? What you’re doing here is EXACTLY what I want to accomplish as well.
Yes, T-Beam, not RAK. I’m going to decline to show the final units so that I don’t have people out there spotting them and taking them over (or outright stealing them). But I’ll give a rough description for your imagination to go wild with.
- Brown UV stable vacuum molded “cone” with a roughly 10" round bottom - about a foot tall. The pointed shape makes it a pretty unwelcome bird perch, and a terrible nesting location.
- Inside cone, a copper cone as a ground plane to a 1/4-wave antenna which is glued to the top of the plastic cone - rough calculations here: 1/4 Wave Ground Plane Antenna Calculator . 1/4-wave antenna was build using some 24" rigid flex coax SMA jumpers I cut in half and stripped back 5", with the shield soldered circumferentially to the peak of the copper cone counterpoise. 1/4-wave length was hand-tuned with a LibreVNA 2.0 (https://www.amazon.com/gp/product/B092SBS32B) to cover the 915MHz ISM band (902-928MHz in USA) There is a bit of a rim in the base of the cone which the copper counterpoise snaps into permanently. A piece of bare (copper-free) FR4 connects two sides of the cone base with non-conductive zip-ties through some 12-ga. solid copper wire (from Romex house wiring) soldered to the inside of the cone, and the T-beam is mounted to that with standard PC standoffs and screws.
- The T-Beam gets a brush application of an MG Chemical UV cured conformal coating to damp-proof the PCB, but I rely on the solar heat of the brown plastic to drive off any moisture inside - this coating is just left in the sun for a day. Battery just gets a weak single ply of Kapton tape over the vent-end, with some NO-OX-ID contact grease (https://www.amazon.com/gp/product/B00HDF9EXE) wiped on the battery holder contacts and exposed battery faces to slow/stop corrosion. Zip tie around the whole PCB and battery ensures the battery can’t fall out when jostled.
- Outside the cone, the solar panel is held onto the plastic cone with 3M VHB tape for 24 hours and then brown RTV silicone adhesive around the edges to seal it up. It sits on a flat that was melted in to the original vacuum pull in a diamond rather than square.
- The base of the plastic cover cone is fingers or barbs of randon cuts folded in after 4" of round tube to align with a post/pole. When the cover cone is presed over the top of a post/pole, the fingers/barbs will keep the cone from being pulled off (you can do it, “but only once”). Think of something like shark’s teeth here.
Basically, one does the tuning and config, verifies function - and then out in the field you just find something with a round top and southern facing sky and pop it on with the solar cell facing south (I’m North America). Takes a second or two (maybe a minute or two if climbing is involved, I haven’t been in shape for years).
Given the angle of the top, you can’t see them from the ground, and you’d have to know what you were looking at to spot in on a post of pole from a distance. These have survived rain and pretty good wind
storms without issue.
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Thank you Tim, I’ve private messaged you as well.
Just a bit of clarification on the 18650 vs 21700 battery. In your photo above showing them in a T-Beam v1.1 side-by-each, you say, “a 21700 battery holder fits the pads of the T-Beam”. Is this to say that the 21700 battery needs a DIFFERENT holder that the one that comes with the T-Beam (for the 18650)? OR, will the 21700 batter ALSO fit in the stock T-Beam holder?
You probably could force a 21700 into an 18650 holder, but like they said in Jurrasic Park 2 “…Violence and technology - NOT good bedfellows!!..” Battery holders are a few cents.
I used properly sized battery holders designed for the 21700. There are side-by-side holders available too - if you top-balance two cells and then put them in parallel on the T-Beam you can extend the runtime even further (>1day).
Basic caveats apply, and you are only limited for modifications of the T-Beam by your budget and knowledge