Sometimes it makes sense to go with plain old batteries and off-the-shelf PVC pipe. That’s the thinking behind [Bertrand Selva]’s clever LoRaTube project.
LoRa is a fantastic solution for long-range and low-power wireless communication (and popular, judging by the number of projects built around it) and LoRaTube provides an autonomous repeater, contained entirely in a length of PVC pipe. Out the top comes the antenna and inside is all the necessary hardware, along with a stack of good old D-sized alkaline cells feeding a supercap-buffered power supply of his own design. It’s weatherproof, inexpensive, self-contained, and thanks to extremely low standby current should last a good five years by [Bertrand]’s reckoning.
One can make a quick LoRa repeater in about an hour but while the core hardware can be inexpensive, supporting electronics and components (not to mention enclosure) for off-grid deployment can quickly add significant cost. Solar panels, charge controllers, and a rechargeable power supply also add potential points of failure. Sometimes it makes more sense to go cheap, simple, and rugged. Eighteen D-sized alkaline cells stacked in a PVC tube is as rugged as it is affordable, especially if one gets several years’ worth of operation out of it.
You can watch [Bertrand] raise a LoRaTube repeater and do a range test in the video (French), embedded below. Source code and CAD files are on the project page. Black outdoor helper cat not included.
Good luck with those D cells lasting 5 years inside the PVC tube.
Can’t speak to their power budget but I’ve had 4x alkaline AAs last for 4 years in similar conditions. No leaks, but I was probably just lucky.
What failure mode do you predict? Moisture? Heat? Any engineering trick to ameliorate this in such an application?
Leaking their chemical guts all over the place.
Caused by…? Mine don’t seem to do that unless they run down very low and nobody takes them out for a long time. Ones experiencing constant use don’t seem to, but I could believe that if you stuffed them in a closed pipe and put them in the summer sun for five years they might
The leakage issue is overstated. There’s always some that will leak, and some brands that push bad batteries, and then people will conclude that all alkaline cells will leak.
I just took out a 9 Volt battery out of a multimeter, still working but complaining, and the battery was made in 2008. No leaks.
OK. Given the dogs breakfast of non-metric pipe and tube IDs available in the typical Home Despot, what’s the appropriate type/size/schedule of pipe available here?
Because sure as heck, if you try to buy a 1-3/8 or 1-1/2 inch ID pipe or tube, it’s NOT going to actually be that diameter.
If i buy it by ID or OD, i have always gotten what i want. So, like, if i buy “1-3/8 inch ID pipe”, the ID has always been 1.375 in, obviously plus or minus a few thousandths.
But as you say, that product / labelling by ID is uncommon here. Generally you buy by “nominal size”, which is different from ID (though sometimes they correspond). I don’t know much about all of the standards, CTS vs IPS vs PVC vs CPVC vs PEX vs sch40 etc etc. I do know the standards are not quite the same as common usage. But i have always found it easy in practice to translate between a specific product i can find and what the actual ID/OD are.
My point is, you have to know what your units are. If you buy 1/2″ CTS and come to be surprised that it is not 1/2″ ID, that’s on you. It’s not exactly a secret that CTS and ID are not the same units.
You go to the store with a D-cell in your pocket. Then you buy the tube where it fits.
If it’s a loose fit, you wrap a piece of cardboard around the cell until it’s no longer rattling around in there.
Has anybody tried to build something like the mechanism from the clock of the long now foundation with a big weight, a long way for it to drop, and some kind of escapement to power an electronic device for years? I wonder if that would work out well at all..
It’s called a gravity battery, and it’s terrible… You need enormous amounts of mass AND a high elevation to be any useful.
According to https://hypertextbook.com/facts/2001/KhalidaNisimova.shtml , one D battery holds around 81 kJ, and according to the gravity battery calculator, 1 ton suspended on 10 meters have around 100 kJ, so less than 1.5 D batteries.
So for the 18 batteries, and using 50 kJ each to be generous, it would be 900kJ, the equivalent of suspending 9 metric tons 10 meters high, or one metric ton 90 meters high.
I’d like to see it, but I don’t expect t to be all useful. My back of the envelope calculation says that if you have a weight of 1 kg dropping 10 cm a day, you’d only have about 1 J of energy for the whole day. One Watt-second. Approx eleven micro Watt continuously. And for a run time of just a year, you already need a 36 m drop.
As where one of the large alkaline D-cells (~65 g) used in this project are at a minimum 18 kWh. That’s about 65k Watt-second or 65 kJ. Having the same energy for thousands of these mechanical contraptions at a fraction of the cost and complexity.
When i saw the headline, i thought it was a hack but maybe a bit lackluster — “i built it and it lasted 5 years” is perhaps worth reporting and definitely can be food for thought, but i wouldn’t generally brag about it. Though i guess i have bragged about things i’ve built that have lasted 5 years, when i was so frustrated with expensive mass-produced products that can’t last one year :)
But “i built it and estimated ahead of time that it will last 5 years” is just a report of wishful thinking. I wouldn’t be surprised if it did or if it didn’t but you will definitely learn about its failure modes after time, and only guess about them without time.
It’s not so much that it will last five years, it’s that it will work autonomously in the wild for five years without downtime or maintenance, which is a bit different. But yeah we’ll see how it works out, I suspect it might develop some problems over time too but then again maybe not.