I have calculated that my daily power draw will be ~0.5Wh and with a 1200mAh battery that should last ~week. I have found that with a 750mA solar panel on my worst day I should generate enough power to fully charge the battery. I believe this should provide sufficient power security.
So if I understand correctly I need a ~750mA diode however the smallest I can find are 1A so if I use one of those should that be fine?
Only thing I’m still confused about is the reverse voltage of a diode to I need to get one which matches my solar panel or battery?
You will have to take care of Forward Current and Reverse Voltage in the specification.
Forward voltage will be small (ideally we would want 0V) but reverse voltage is the voltage that should be safely blocked so this should at least be the ‘open output voltage’ of the solar panel (which is bit higher than is its nominal output voltage).
For a 5V-7V panel something like a SS12 or similar with reverse voltage of 20V should therefore be sufficient.
Unless an engineering miracle occurs, you’re likely to get an OKish result but unlikely to get the results you were expecting.
This is why we have to try things out. Getting in to too much detail until you have some experience (like about 4 or 5 deployments) is somewhat academic.
Ideally, you get an INA3221 so you can log voltage & current from the solar panel, the voltage & current (in & out) for the battery, and the voltage & current to the device. Bear in mind that the device will peak for short intervals so you need to capture that info more frequently.
This will give you lots of data to do some modelling and provide a setup that allows you to swap different components around.
Free tip for today: Point the solar panel with a tilt towards the east, so it gets more direct sunlight in the morning when the battery will have had some use overnight. If you get the right combination, you can have the battery full by early afternoon on a sunny day so it’s ready for the night.
For those who find this interesting, below an overview of the battery status during 3 days of a Cubecell setup with the standard LoRa sketch from the manufacturer. Measurements are taken every 15 minutes, via TTN to an InfluxDB and Grafana. I use a cheap LiPo battery (labeled 1400 mAh) and a cheap 90x60mm solar panel. As you can see the battery, with an average cloudy sky in the Netherlands, remains full and on voltage.
Thanks for sharing. At first glance this may give the impression that the configuration will run solely on the solar panel the whole year but reality is a bit more complex:
The above measurements of (only) battery voltage over a limited number of 3 consecutive days (from a total of 365) are not representative for the amount of energy (battery charge) that was produced by the solar panel. Neither is ‘an average cloudy sky’ representative for the amount of received solar energy.
I previously posted here about having sent 72000+ uplinks with a HTCC-AB01 board on a single 1200 mAh Lipo battery charge (without solar panel). After 72000 uplinks the battery voltage was still 3.69V.
Let’s assume that I started with a full battery voltage of 4.2V and that the battery voltage (on average) decreased linearly with every uplink message. That means a decrease in battery voltage of (4.2 - 3.69) / 72000 = 0,00000708333 V per uplink message.
You sent about 4 * 24 * 3 = 288 uplink messages in those 3 days. With an oversimplification of reality, compared to above calculations from my test, that would cause a decrease in battery voltage of about 0.00256 V over those three days (for sending 3-byte uplink messages without sensor measurements). Your battery capacity is even larger so voltage should even decrease less. You are measuring/reporting with two decimals accuracy and therefore won’t notice such small decrease.
I only did send uplink messages during my test without performing any sensor measurements so your configuration will probably draw a bit more current while not asleep.
This probably explains why you see the variations in battery voltage (over a 0.02 V range) during those 3 days. The decreases caused by consumption of the board and sensor and the increases caused by charging from the solar panel.
Not really. Your graph shows an average 0.01V decrease in battery voltage over the 3 days in September which indicates that the battery did not get fully recharged by the solar panel. When extrapolated the decrease is 1.22V for a full year. September is not one of the least solar productive months. Expect much less charging during the autumn and winter months. Consumption will not change so the battery will drain more during those months (and battery voltage will drop accordingly).
Example of distribution of monthly in-plane radiation for fixed angle for some Dutch city.
If you want to use battery voltage as indictor to see if the battery and solar panel are sufficiently dimensioned, this will require measuring battery voltage over a much longer period that should include some of the least solar productive months.
Please don’t blame me for posting this message here. I meant to be nice but I’ll never do it again. How could I be so stupid so please accept my humble apologies.
Nice and welcome that you share your experience and measurements!
Your conclusion “battery remains full on voltage” is incorrect however.
0.01V decrease in 3 days may seem unimportant (or go unnoticed) but in the context of battery powered LoRaWAN devices it surely is relevant.
My response was to temper unrealistic expectations from battery and solar panel combinations (and explain a bit why), while you probably only wanted to share your results.
There are people with different levels of experience here on the forum so it happens that people with more experience on a subject step in to help by providing additional information, but can sometimes also be critical about less correct/incorrect statements because these may result in unrealistic expectations for other users. No pun intended.
You are both on the naughty step - can someone move this actually very useful discussion* to the very thread that @bluejedi split out.
It’s very useful because compare & contrast of scientific methods is so much more informative than just saying “Do this”. And there is always someone with more expertise we can learn from. Viva la Forum!
The thread you are refering to is about how to mount a solar panel so that would be off-topic.
Above discussion is about CubeCell battery usage and solar charging so it is actually on topic here.
have been experimenting with some samples of the Cubecell and the related ‘wireless stick’ ESP32 versions and so far this seems like a very very nice package, especially the cubecell that includes the solar charging circuit. I have some old solar panels lying. Haven’t reviewed the documentation in depth yet but I assume that the charging circuit is setup for Lithium Ion (i.e. up to 4.2V) and not for LiPo?
All in all a very nice, well packaged alternative (usb,solar, rgb led) to the earlier and power hungry ESP32 TTGOs I was using.
I’m also designing some 3d printable packaging to place the nodes, the antenna and a battery in.
Hi Paul, I am a phd student looking into setting up an IoT network to monitor interception and throughfall using tipping bucket rain gauges in a forest in Wales.
your experience could be very useful to me, could we talk?
I’m recently using a CubeCell Module (bought it about 6 month ago). Code works as intended (I’m basically reading the ADC and send it as Highbyte-Lowbyte to TTN):
Connecting also works fine and I can see around 60 messages being send to the TNN. I do no move my device nor the gateway - yet, no messages are receveid.
The code I use is the example LoRa code in Arduino, I just modified the LED itself. This weird behavior happened before, too. Also the number of messages send differs. Does anyone have any idea?
Uptime of the device is about 2 days till it does not send anymore, frequency of sending is every 15 minutes (gateway is about 20m away)
Maybe you have some tips for debugging? I just can think of restarting the device though it feels weird as the optimal solution.
You will need to provide a bit more detailed information, like:
Which exact sketch are you using.
What do you mean with “no (more) messages are received”?
Do you mean the messages are not visible in the TTN console application/device log?
Or do you mean your application that reads data from the TTN backend does not receive messages (anymore)?
To be honest, I don’t know what is the reason for no messages being received. Its either the device not sending anymore or the gateway or TTN not accepting anymore. As I am not sure how to debug this, I wanted to ask for help.
What I wanted to explain in my message was basically this: No messages being send happens on different devices (yet all are cubecell modules) on different applications and all have in common that some messages ARE send, authentication done via OTTA. Neither device nor module are moved (to rule out many errors as no connection, faulty device etc.)
