I developed a node with a motion sensor. The MCU is woken up by the motion sensor, turn on LED and send out a short LoRa packet for 5 seconds. This program works fine when I powered it by an external 3.6V DC supply.
When I plug in a brand new 1/2AA Lithium Thionyl Chloride battery from Lunggwey 3.6V 1/2AA 1200mAh. The voltage drops to 2.5 V during the 5 seconds on time with LoRa transmission.
Is this a battery problem? Any suggestion?
I did more measurements with the CubeCell 1/2AA board. I compared the results from a DC supply, a D lithium cell and 1/2AA lithium cell. Here are the results:
(1) DC supply - set to 3.6V, 3.2V and 2.8V. The LoRa packet was delivered OK in all 3 settings. Supply voltage dropped about 0.1V from DC source during radio transmission. . Peak current was up to 60-70 mA instantaneously,
(2) D cell - The LoRa packet was delivered OK. Supply voltage dropped from 3.58V to about 3.51V during radio transmission.
(3) 1/2AA cell - The LoRa packet was lost. Supply voltage dropped from 3.5V to about 2.9V during radio transmission.
The CubeCell 1/2AA board comes with a socket for 1/2AA battery. I certainly like to use the built-in 1/2AA battery socket. Any suggestions on how to make the 1/2AA battery to work with the LoRa radio?
I would have thought it unlikely that the radio is the problem. The radio, when transmitting, does draw much more current than the processor but these boards are designed to perform these [basic] functions on battery power. However, I am currently (no pun intended) dealing with a problem with a flow sensor that runs just fine (5V or 3.3V) when the processor is powered through the USB connector (i.e. 5V/1A) but dies when running on battery alone (even when the radio is idle).
So my question would be “Are you sure it’s the radio that’s the real cause of the voltage drop, or is it your motion sensor?”
Thank you for your input. I further verified that the problem is due to the 1/2AA Lithium battery which cannot supply sufficient transient current during LoRa radio transmission. I used a 3.7V 700 mAh Li-Ion battery to power the board. it worked fine and voltage did not drop at all, stayed at 3.7V during LoRa transmission.