Solar Mesh node update.
The thermal switch has worked exactly as expected opening at freezing thus isolating the solar panel from the charge circuit and the battery.
This is done to prevent damaging the LiPo battery.? Charging when the cell is below freezing is a no-no.
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So far, the longest "off" period was almost a week before the weather warmed and the sun recharged the 3.7 volt 3 Ah LiPo battery.
Fortunately, the node is lightly used and very frugal with it's Watts, so it stayed on with some power to spare (30%).
The next goal is to use the solar electricity to heat the battery up, allowing it to charge when the sun is shining on those below freezing days.
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After some trial and mostly error, I believe I have a circuit simple enough for others to make.
The idea is to sense when the thermal switch has opened isolating the solar panel from the charging circuit.
This, in turn, shunts the solar panel current through a 20 ohm resistor at 5 volts generating 1.25 Watts of heat.
The resistor is a larger surface mount variety laying on a double sided copper clad circuit board which becomes a heat sink.
Some short wires soldered to both sides transfer the heat to the pcb bottom and the battery.
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By using a P channel MOSFET I was able to do it all with one device, an IFR9530 3 legged TO-220.
It's gate senses the volts on the thermal switch out, turning on hard when the switch turns off and vice versa.
The 100k pull down resistor insures the MOSFET gate goes low while a blocking diode built in the node's solar charge circuit prevents any back flow from the battery.
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Here's the yet to be populated circuit board as it would sit next to the thermal switch atop the battery.
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Here's a crude schematic of my idea.
It worked FB on a breadboard so I'm taking the next step.
Once the resistors show up I'll be able to finish building and install it.
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Here's where the completed heater circuit will be spliced in and mounted on the battery.
I'll lay a toothpick between the sensor and the heater to keep it from warming the sensor directly.
The battery lays on a foam pad to insulate it from the case.
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Next installment will have the heater installed and running.
Then test to fail.
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73
Mike N0QBH
N0QBH Mike Berg