PCB with parts soldered on and wired for testing the actual circuit.
The main concern is how hot at full output (1.25W).
Tie wrapped to the battery and un-insulated brought the battery temperature up about 20 deg F above surroundings.
The pcb alone with only air to cool it rises to about 140 deg F after 10 minutes.?
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The switch mimics the function of the thermal switch.?
In operation the thermal switch opens when the battery temp drops below 32 deg F.
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Switch closed (on) MOSFET gate is high - no current - no heat.
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Switch open (off) and the MOSFET gate goes low - turned on. Almost 1/4 Watt.
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Next is to install the heater in the solar powered node and see how the idea fares in the real world...
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73
Mike? N0QBH
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N0QBH Mike Berg