Battery options

[Dylan]

Hello,

I am wondering if it is essential to be using LiPo batteries or if we could use other types of batteries?

The reason behind this is I am looking to increase the battery life by using solar charging or any other type of charging capacity available, perhaps even a combination. I don't really have the option of changing the battery as the pycom device will be used for on animal tracking.

The aim is to get a device running for 1-2 years recording a signal and sending it via lorawan every 15-30minutes.

I'm not expecting 1-2 years that for sure, but its the end goal so may as well aim for it from the beginning.

I have seen https://www.adafruit.com/product/390 which looks great but sticking anything bigger than about 60mmx60mm (solar panel) on an animal gets difficult.

So, can I use a battery that could be trickle charged?

Any ideas would be greatly appreciated.

[nathanh]

For that kind of longevity you're better off ditching the secondary cells (rechargeable) and going for a primary cell. I would recommend looking at the SAFT LS or LSH series. They are the best energy density to size batteries available.

[Dylan]

@jcaron Thank you for the advice :D. I'm looking forward to being at this stage of the project. I'm bound to have plenty more questions, and I'll put any success here in case someone else is trying it (could be many weeks away until I start actual trials though).

[jcaron]

@dylan When you want to run for a long time on battery, you have the following parameters to take into account:

• battery capacity (C)
• how much current you draw during sleep (I1)
• how much current you draw when awake (I2)
• how long you sleep (T1)
• how long you are awake (T2)

Your average current draw is then: I = (T1 * I1 + T2 * I2) / (T1 + T2)

For intance, if you wake up 10 seconds every hour, and draw 50 mA when awake and 10 µA when sleeping, your average current will be about 150 µA.

And your battery life is C / I, so a 2500 mAh battery with the above current draw will result in a nearly 2-year battery life.

But if you wake up every 15 minutes instead, your average current jumps to over 565 µA, and your battery life is now only 6 months.

In most cases, with the current behaviour of a LoPy, the "awake" component (T2 * I2) will be predominant, so you want to wake up rarely, and for a very short time. Don't forget that with LoRa on a moving animal, you'll want to use SF12, which means you'll be awake at least about 4 seconds, during which average current is about 50 mA, possibly a bit more. If the LoRaWAN network you connect to sets RxDelay to high values, you can easily double that. But if you need to get a GPS fix, then you'll be awake a lot longer than that, and that will kill your battery.

During deep sleep, you can go down to about 10 µA, but it's horribly easy to increase that to much much higher values by turning on a sensor here or there. At the moment, just enabling accelerometer wake-up on a Pysense or Pytrack will add over 300 µA, for instance. This will kill your battery life as well. Not quite sure if the GPS chip on the PyTrack has a sleep mode, how much it draws in that mode, and how long it takes to get a fix when waking from sleep.

Back to the original topic, you can use other batteries, but one important and often overlooked factor is that you need a battery that can deliver the relatively high current needed during startup. LiPo batteries are pretty good for that, others not quite so.

[seb]

Feel free to mention any common mistakes that could blow up the Pycom device :P.

The 3.3v pin is output only dont feed power into it. Vin is rated to a maximum of 5.5v anything above this will damage the voltage regulator.

[Dylan]

@robert-hh Excellent, I was just reading some of your posts, somehow I missed it in my original search. Certainly the 1-2 year aim will be on a different and probably custom designed lora device. But for now we will use the LoPy/FiPy, I'll have a google tonight for some possible battery + charging options for it. Some fun homework.

Feel free to mention any common mistakes that could blow up the Pycom device :P.

Cheers for the help.

[robert-hh]

@dylan You can use any battery (set) that supplies a voltage between 3.4 and 6 V and sufficient current. Besides that, as much as I like Micropython and the PyCom, using a LoPy for your purpose seems inadequate. There are much smaller boards which provide Lora only.
Although programming with the xxPy devices is much more convenient.