Hi
I have a project running on battery, per today single cell LiPo 2000 mAh.
System drags 8mA, and each hour a LoRa message is sent that uses 70mA for 2 sec. Lasts for around 90h with no solar charging.
I'm concerned using and charging while really cold due to chemistry that is not meant for cold days.
Any tip for battery that can survive this cold?
M
I don't know of any commonly available battery chemistries that like being charged at temps below freezing. It damages LiPO, I suspect. You can probably reduce the charge rate to reduce the damage, but that might mean wasting your precious solar power when it's available.
Maybe insulate the battery and even put a small heater element inside the insulation to get the battery above freezing before charging it?
Cells are available for use under extreme temperature conditions.
A regular Lipo can work to -20°C.
Charge above 0°C.
Don’t buy a Tesla if your area gets cold
Avoid EVs all-together.
LiPo is the worst choice.
NiMH and Lead-acid still rule below 0C.
See this page (click).
Leo..
"this cold" is quite relative... You are charging with solar, so when sun is shining. What's the temperature in this condition? If -10'c you are out of luck with lifepo4 batteries. If closer to -5, you could build an absorbing battery enclosure that is heated by sun as well. Except of charging, Li batteries should be fine in "this" cold weather.
Hi, that was a nice web page, thanks.
FYI. Here in Norway we uses EV all the time, 26% of cars are electric, I have also one, best decision ever compared to my mercedes diesel, EV is far better economy. A lot of teslas, and they work satisfying also in cold.
Norwegian statistical agency (no fake news)
Nysgjerrig på elbiler i Norge? Se siste elbilstatistikk her – SSB.
You could consider supercapacitors, they work well at low temperatures. I have a similar system with a small solar panel and only 2 small supercaps of 5F each.
It takes some weather samples every 15 minutes and sends it via WIFI every 1 or 2 hours, depending on the charge. The rest of the time it's in deepsleep consuming about 10uA.
Without any sun it survives more than 48h. And you could put more capacitance, 40, 80F...
It's running for more than one year, but we didn't reach -10c here, maximum (minimum) -2c.
Hi LarryD, im not into counting and stuff for my EV, I got hold of an older Leaf (from my son), for using around house/town. It is better in summer than in winter, maybe 20-30%, 2016 model. The car is perfect for that use, if I go longer trips I use my MB, like 3 times a year. Yes, I do not drive much.
In general I think that EV owners are pretty happy, my brother and a friend is super happy. Must mention that we have very good charging infrastructure if you need to drive more than 400 km.
If you want to get real info there is a group on FB TESLA | Facebook in Norway, you probably can participate and ask questions in English.
The best thing you can do is read the data sheets available for various battery chemistry , then make your choice
This is interesting, thanks!
What charging IC do you use for the supercapacitors?
Do you also use an RTC to control this?
As the solar panel is a current source (and small, 6x8 cms) you don't need a charging IC. What I have is a boost converter to 5V (the supercaps are 5.5V) and then a LDO to 3.3V.
This way you make sure that the supercaps get always charged even with weak sun. It works very well, with sun the caps are charged in a couple of minutes.
Do you also use an RTC to control this?
No. The MCU is checking the voltage level of the supercaps and adjusting the sleep and sending time according.
During the day the caps are always at 5V, so it doesn't matter, it sends the data every 15 mins. When the charge goes below e.g. 4.9V, then it takes samples still every 15 minutes but connects to the WIFI only every 2 hours.
Even when it rains all day, in the central hours the panel still charges the caps. It almost never goes below 4.5V.
System drags 8mA, and each hour a LoRa message is sent that uses 70mA for 2 sec
The most important is to keep the consumption low most of the time. 8mA is too much, you should lower it if possible. I'm using the ESP32-C3 and it consumes only 10 uA in deep sleep.
You could also consider a hybrid solution, with battery and supercaps. It has some advantages, makes the battery life longer.
You could also try sodium-ion batteries.
Thanks for this good answer, I will look into it, and maybe copy it 
My 8mA will change, I add 2 mosftets to my 3.3 and 5v rail (exept ESP32 wroom-32) to switch off all sensors and LoRa. Send as you, if bat ok, each 30 min, if low, each 2h, or maybe once pr day (data is not so important to read often in winter time).
Here is the complete schematic:
The ESP8685 is the same chip than the ESP32-3C, but a bit smaller module. It's a nice RISC-V IC, single core and with very low power consumption. The resulting PCB is quite small, depending on how you mount the supercaps.
You can program the MCU directly with the USB-C connector, so you don't need the serial adapter and connector.
The jumpers J1,J2,J3 are there to avoid that the USB and the caps are connected together, when you want to program it. Otherwise when the caps are empty they could drag too much current from the USB.
This one, can you pleas give me specifications for IC?
In the previous version I used one simple module like this; 0.9V - 5V to 5V boost converter:
It works perfectly fine.
Now I have designed one with this IC: TPS61220. It works the same more or less.
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