Electronics > Projects, Designs, and Technical Stuff
Solar Powered Low Power Embedded Device
Kalcifer:
--- Quote from: Conrad Hoffman on July 01, 2020, 01:10:10 pm ---Can you get the job done with a super capacitor? How about a primary battery that you change every few years, because you'll probably be changing your rechargables that often anyway.
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I've been strongly considering and looking into just using a supercapacitor. It seems to check the box for reliability and safety. It's easy to predict, and simple to deal with. I'd definitely have to regulate the voltage somehow but that's no biggie. The only trickier part is finding a way to do it without large quiescent currents sucking up useful power.
As for the primary battery that i just recharge every few years, I was initially looking into using i lithium ion cell like an 18650-30q as the main power source. by my math, it'd last just over 2 years in an ideal scenario, but theres a few caveats for me.
1. I'm too lazy to charge a battery ;P /s
2. Since I'm strapping this to the side of my house, I'm not super confident in the safety of a circuit using a lithium ion without an proper battery management system. I don't want to burn my house down.
3. I really love the idea of self sufficiency and autonomy of solar power. It just feels so simple and elegant having it all run on its own.
NiHaoMike:
--- Quote from: Kalcifer on July 02, 2020, 01:35:48 am ---I've been strongly considering and looking into just using a supercapacitor. It seems to check the box for reliability and safety. It's easy to predict, and simple to deal with. I'd definitely have to regulate the voltage somehow but that's no biggie. The only trickier part is finding a way to do it without large quiescent currents sucking up useful power.
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There are micropower voltage detectors that will work, or if the load includes a microcontroller, you can have it check the voltage every time it wakes up and alter its power usage in some way, for example by turning on some sort of load (e.g. a LED) or changing its sleep time.
Kalcifer:
--- Quote from: NiHaoMike on July 02, 2020, 02:00:07 am ---
--- Quote from: Kalcifer on July 02, 2020, 01:35:48 am ---I've been strongly considering and looking into just using a supercapacitor. It seems to check the box for reliability and safety. It's easy to predict, and simple to deal with. I'd definitely have to regulate the voltage somehow but that's no biggie. The only trickier part is finding a way to do it without large quiescent currents sucking up useful power.
--- End quote ---
There are micropower voltage detectors that will work, or if the load includes a microcontroller, you can have it check the voltage every time it wakes up and alter its power usage in some way, for example by turning on some sort of load (e.g. a LED) or changing its sleep time.
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The load is indeed a microcontroller, and that's a good suggestion. I will keep it in mind.
I was thinking of just putting a zener diode more or less in parallel with the capacitor that has a really low reverse leakage current. Something like the BZX55C4V7-TR. Passively accomplish the same idea.
Side note, what do you mean by a voltage detector? Is it able to do something when it detects a voltage? Could you give an example of said device?
NiHaoMike:
--- Quote from: Kalcifer on July 02, 2020, 02:52:28 am ---Side note, what do you mean by a voltage detector? Is it able to do something when it detects a voltage? Could you give an example of said device?
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Here's one example:
https://www.maximintegrated.com/en/products/power/supervisors-voltage-monitors-sequencers/MAX6375.html
It's a very low power comparator with its threshold set at the factory. When its supply voltage goes above or below that threshold, its output changes states accordingly. The biggest catch is that if you order some, review the part number very carefully to make sure you get the correct voltage!
Such chips are often used in simple battery balancing circuits, one per cell. When the voltage goes to the balancing point, it turns on a load to drain a little charge. In my 4S, 82Ah LiFePO4 pack, I added flashing RGB LEDs across the load resistors so they flash when the balancing circuit is active.
Kalcifer:
--- Quote from: NiHaoMike on July 02, 2020, 03:04:21 am ---Here's one example:
https://www.maximintegrated.com/en/products/power/supervisors-voltage-monitors-sequencers/MAX6375.html
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Very cool! That will come in handy. For this case, what would be the pros and cons of that when you compare it to say just using a zener diode with its reverse leakage current being similar to the quiescent current of that device? The main pro I could see of using that chip is that it offers more customizability/functionality with how you want to handle the overvoltage event.
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