Hello all,
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See paragraph 3
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I'm fairly green when it comes to electronics but I have been tinkering for a couple of years now and am trying to get my feet wet with a fairly typical "solar shed" scenario. I have a 12V 7Ah Yasua battery (not a deep cycle leisure battery, but don't care if it doesn't last too long). I have a very low quiescent current DC-DC step down regulator to 5V permanently connected to a Wemos D1 mini (esp8266 based) wifi microcontroller. I intend to have this in deep sleep a lot and wake up periodically to check the amount of solar being generated, current draw and voltage of the battery as well as temperature inside the shed just for the heck of it. It will also check with a message broker on my server in the house to see if it has been told to wake up and turn the lights on, at which point it will come out of sleep mode for a longer period of time to drive the LEDs I have. It will be connected via a GPIO pin to a 5M strip of WS2812 individually addressable RGB LEDs that will run round the outside of the shed (for BBQs, parties and randomly scaring the cat etc.). It will be a lot like the project on instructables here:
http://www.instructables.com/id/Shed-12v-Solar-Lighting-System/, but with a microcontroller and some sensors.
Now the WS2812's run at 5V, so while I could connect them to a larger DC-DC step down and also have the microcontroller connected to that, it seems wasteful of precious mAh's as each chip on the WS2812 still draws about 1mA or so even if all RGB led values are set to 0. Overall it would be a constant current draw of at least 2-300mA when 'off'. My thoughts are to have another DC-DC step down converter to 5V but much higher rated (10A+), to drive from each end of the LED strip. So that the regulator and LEDs aren't drawing current 24/7 I intend to put an N-channel MOSFET between the 12V GND wire of the regulator and the "12V load" GND terminal connector PWM solar controller / load regulator. The gate of the MOSFET will then be driven by the WeMos at 3.3V. I have found a MOSFET (i forget the model # now) with TTL level input and very low RDS(on). I will try it direct at 3.3V logic from the WeMos GPIO pin, but could drive it via a transistor connected to the WeMos 5V input if needed to drive the gate voltage slightly higher, but I think the heat dissipation with my heatsink should be OK even at only 3.3V.
My question, as per the subject line, is the 12v -> 5V dc-dc converter an inductive load, and therefore do I need a flywheel diode to protect the MOSFET? I have googled this but without much success, lots of results relating to relays, coils and DC motors. As far as I can tell the step down converter is a switching LC device that uses an inductor and capacitor with its own diode internally to "switch" on and off the input voltage and use the reverse biased diode (when on) as a path to provide current (along with the capacitor) when the input voltage is switched off. What I don't know is if there will be a corresponding kick on the Vin side of the regulator. Do I need a diode in my configuration? Is there any cost to adding a flywheel diode? (bearing in mind I am looking for low power consumption when off, and don't particularly care about rapid switching time).
Thanks for reading.
The DC DC buck converter I intend to use
https://www.aliexpress.com/item/DC12V-24V-to-5V-10A-50W-Step-Down-Converter-Buck-Voltage-Regulator-Module-Waterproof-IP68-Accessories/32847316670.html