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I have a PCB powered by a lithium battery , it works well inside the house, but when I leave it exposed to low temperatures with humidity the PCB or the battery stops working. I leave the PCB in the backyard "garden"of the house inside a waterproof box where temperatures at this time reach perfectly 1 degree celsius, it works correctly until to become night, when the temperature drops.

Could it be that the humidity, the low temperatures are causing the electronics to fail? (Only one day it showed signs of oxidation, despite being protected by the box)

this is the evidence of oxidation

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    \$\begingroup\$ put a heat source inside that box, to avoid condensation. \$\endgroup\$ – analogsystemsrf Aug 1 '19 at 12:40
  • \$\begingroup\$ whats , are you kidding me \$\endgroup\$ – asterix Aug 1 '19 at 12:42
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    \$\begingroup\$ it is a IoT experiment maybe it is not good idea a heating resistor :( because battery life \$\endgroup\$ – asterix Aug 1 '19 at 12:51
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    \$\begingroup\$ Another idea is assembling the box on a harsh dry and very cold day, put silica gel in, then seal it. \$\endgroup\$ – Janka Aug 1 '19 at 12:53
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    \$\begingroup\$ What exactly is this device? What sort of current draw does it have versus time, ie what is the average and what is peak? Many battery types do poorly in cool temperatures, LiPo cells such as yours can see their peak current performance seriously reduced. It may be that something like some disposable alkaline flashlight batteries would solve your practical problem. Also do not overlook the possibility of software bugs causing failure when the temperature goes negative! Fortunately most of us have a handy subzero test chamber that usually leaks enough RF for a signal to get out... \$\endgroup\$ – Chris Stratton Aug 1 '19 at 13:15
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To prevent condensation the components in the cabinet should be above the dew point.
There are two ways to do that:

  • Reduce the relative humidity, for example with silica gel.
  • Increase the temperature, with a heater.

When cold the chemistry in the battery slows down. Which increases the internal resistance of the battery, reducing it's effective capacity. Refer to the battery datasheet to view how much you lose.

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