18650+StepDown+low temperature = crash

[gphormaz]

Hi everyone,

I'm trying to make a DHT22 with an arduino nano+sim800l. It's designed to work below 0 (-17° to 0°C).

The circuit i have is something like this:




The problem is that, after few mins, the sim module was not able to connect to internet, and after two hours, was totally off. Measuring the batteries, one of them was 3v, the other one 0.11v (fucking fake batteries)

So I changed the batteries for samsung ones, and i started to measure the voltage supplied to the sim module. (analogRead(A0)*5/1023)

It was working perfect for 5 hours, until....



If i call to the number, it's with tone (connected to the cellphone network), but it's without internet (so i'm not reciving data)


I don't know what could be the problem; do i need to change the step down?, do i need to search for anoher power supply?

Thanks for the help!

The modules i'm using are:
Step down: lm2596
BMS: 2S 15A HX-2S-D01
Arduino: nano v3
Sim: sim800l
Temp: DHT22

[arduarn]

Interesting what you are doing. Don't have any relevant experience, but I'll throw out a few ideas/questions anyway.

Your schematic is crap, but you probably know that already. Any photos?
You say -17oC to 0oC, but the chart seems to indicate as cold as -40oC; which is correct?
The performance of components like electrolytic capacitors will significantly change at low temperatures.
Battery performance, even with Lithium Ion batteries, will likely suck.
A GSM module has quite a high short term peak current requirement and will need a good supply; will a cold battery cope?
The voltage in the chart rising to 5V may be an indication of a flagging battery. If the supply to the Nano falls below 5V then the analog reference will also fall below 5V and may therefore make your calculated analogRead value go up.
Do you have a link to the exact BMS since it is not clear what it is.

Suggestions:
If you can, monitor the voltage level from outside of the cold space using a multimeter.
Alternatively, go low level and configure the ADC registers manually (instead of using analogRead) and use the internal 1.1V band-gap reference as the analog reference. You'll need a voltage divider to bring the input voltage into range.

[mauried]

Lithium Ion batteries perform poorly at low temperatures, -20C or less.
Capacity is reduced and they are very hard to charge.
Id use NIMH batteries for this type of project.
 

[jremington]

Most SIM modules are designed to run from a single Li cell, and the Arduino will run on one too. Get rid of the converter (which may not be able to supply the peak current required by the module) and use your cells in parallel.

[Wawa]

+1
Some SIM modules made to be used with an Arduino run on 5volt, because they have two diodes in series between +5volt and SIM supply. If you bypass the diodes, then you can run the module directly off a single LiPo battery (or two in parallel).
If you use an 8Mhz Arduino, and remove/bypass the 3.3volt regulator, then you can also run that also directly off one LiPo.
Not sure about using a DHT22 outside.
Leo..

[gphormaz]

You say -17oC to 0oC, but the chart seems to indicate as cold as -40oC; which is correct?
The performance of components like electrolytic capacitors will significantly change at low temperatures.
Battery performance, even with Lithium Ion batteries, will likely suck.

A GSM module has quite a high short term peak current requirement and will need a good supply; will a cold battery cope?

The voltage in the chart rising to 5V may be an indication of a flagging battery. If the supply to the Nano falls below 5V then the analog reference will also fall below 5V and may therefore make your calculated analogRead value go up.
Do you have a link to the exact BMS since it is not clear what it is.

Suggestions:
If you can, monitor the voltage level from outside of the cold space using a multimeter.
Alternatively, go low level and configure the ADC registers manually (instead of using analogRead) and use the internal 1.1V band-gap reference as the analog reference. You'll need a voltage divider to bring the input voltage into range.

it's -4.0 (blynk app adjust the zoom)

Yes, i returned home, and with the tester was 4.2v not 5, so i guess you are right with that. Would you recommend to change to Nimh battery as mauried said? NiCd?

BMS: Li-ión Lipo 18650 2S 15A HX-2S-D01

It's strange... i programmed now to force the restart/reconnecting the module after 1 minute without internet, and it's working (intermitent) even with the read of 5v from the analog.

[jremington]

Would you recommend to change to Nimh battery?

No, see replies 3 and 4.

[gphormaz]

Most SIM modules are designed to run from a single Li cell, and the Arduino will run on one too. Get rid of the converter (which may not be able to supply the peak current required by the module) and use your cells in parallel.

Tried...

this sim module needs a supply between 3.8 and 4.4v, otherwise does not work. With the temp decrease, the stand alone battery it's not able to power up the sim module. The step-down let me supply a constant 4.2v.

[Wawa]

...this sim module needs a supply between 3.8 and 4.4v, otherwise does not work.

Which SIM module (post a link).
Did you understand the part about the two diodes in series?
See this diagram, top/right.
Leo..

[gphormaz]

Which SIM module (post a link).
Did you understand the part about the two diodes in series?
See this diagram, top/right.
Leo..

This one... not the micro-only;

http://www.ifuturetech.org/product/sim800l-gprs-gsm-module/

Instead of the battery, is the dcdc step down based on lm2596

Thanks!

[Wawa]

That one doesn't seem to have the diodes, so it SHOULD be able to run on a single LiPo.
Not working below 3.8volt could mean a bad battery or bad/thin/long wiring between battery and module.

DC/DC converters have a constant idle current. Not good for battery longevity.
Leo..

[jremington]

The product page for your module clearly states the supply voltage range:

Supply voltage range 3.4V ~ 4.4V

If it cuts out at 3.8V you are doing something wrong, or the module is defective.

[r0b0t0ne]

Hi,
were you ever able to resolve the problem that you had with your setup at low temperatures?

I ask because I have a similar project - a sim800+arduino nano+lithium Ion battery (1500mA).

I have been testing it as room temperature and all is okay, and it sends me a status text every 20 minutes. But when I leave it in a cold temperature - for example, outside, where the temperature is approx 1 deg C,  the setup begins to malfunction. It appears to send me a text and then the setup appears to reset and then continue to reset at one minute intervals and send a text at each one minute interval. When I bring the setup indoors, within a few minutes it goes back to normal.

I think it is the lithium battery which is the problem. I changed the battery with another lithium battery and get the same results. A search on google leads me to believe that a lithium battery is not the right technology for my setup, as I am planning to use it for outside temperature measurement. So would be interested to know if and how you fixed the problem.

thanks

[ShermanP]

I have the same question for powering a Wemos D1 Mini mailbox notifier.I guess all batteries suffer in the cold, but always thought lithium was the least compromised when cold.  Now I'm not so sure.  One problem with NiMH is self-discharge, which you don't get with lithium.  I need to be able to source around 200mA, and thought one 18650  would do it.  Anyway, I hope the battery experts here can clear this up.

[jremington]

Discharge voltage of an 18650 Li-ion cell at 3A and various temperatures.
Cell type: Panasonic NRC18650PD, 2.8Ah nominal, LiNiCoAlO2 (NCA)
https://batteryuniversity.com/learn/article/discharging_at_high_and_low_temperatures