Solar powered DC motor for a project outside - Page 1
Forum section: electronics / projects

author: captainkanpai
author_rank: Newbie
timestamp: January 14, 2023, 12:33:09 pm
content: Hi everyone!For a sound-art project that will be standing outside, I'm trying to figure out a way to solar power a 12V DC motor that turns on depending on the amount of sunlight.This way I'm hoping to have the installation only on during the day while charging enough to have enough power for at least two weeks.In the picture below I have the current setup I am trying to make work.It's 3 times 2 solar panels in parallel to create 200mA, going through a 5V step-up-down converter into a TP4056 with a 6,8K rprog resistor.These three TP4056 charge a 21700 cell and are then also in series to create around 12-18V to power the DC motor and ESP32.For this, I'm thinking of using that load-sharing schematic to use the load from the TP4056.The ESP32 then controls the DC motor with a TIP120.So far I can get things to work separately, but also have some problems with the step-up-down buck converter.Somehow the module just stops working overnight (for no reason...?), while only being connected to the TP4056. (I disconnected everything else)The converter does still work with my bench power supply, but not with the solar panels anymore.I measured the motors taking around 100mA max, without having anything connected to them.The ESP32 takes around 40mA.So with the idea of having 6 solar panels, it should be enough to almost not draw anything, right?Am I doing it all wrong?Are there maybe any better solutions for this?I'm just a beginner and don't want things to go up in flames.Especially since I can't be close to this permanent work the whole time.Looking forward to hearing from you!Cheers and thanks

author: Zero999
author_rank: Super Contributor
timestamp: January 14, 2023, 11:48:07 pm
content: Have you actually measured the solar cell voltage? Does it go too high?

author: captainkanpai
author_rank: Newbie
timestamp: January 15, 2023, 12:41:14 pm
content: Yes, somehow the voltage of the solar cells adds up extremely quickly.In cloudy weather (unfortunately haven't had sun in a while) and with the use of LED lights, I quickly get up to 5V.

author: TheMG
author_rank: Frequent Contributor
timestamp: January 15, 2023, 04:38:59 pm
content: Solar panels behave somewhat like a constant-current source. If there is little or no load, the voltage will rise to near maximum even with relatively little light shining on the panel. The more light hits the panel, the more current it is able to deliver. If you try to draw more current than the panel can deliver under existing light conditions, the voltage (and thus output power) will drop off very quickly.These characteristics of solar panels need to be taken into account when designing any kind of system that uses them.

author: NiHaoMike
author_rank: Super Contributor
timestamp: January 15, 2023, 10:40:26 pm
content: Try directly connecting the solar panels to the TP4056?

author: JimRemington
author_rank: Regular Contributor
timestamp: January 17, 2023, 05:20:38 am
content: A much simpler and more reliable approach would be to use a small 18V solar panel to trickle charge a 12V lead acid (gel) cell, which would power the motors directly, and any associated electronics via simple step down converters. The batteries can also handle the start/stall current of the motors, which is 5 to 10 times higher than the running current, something your boost converter probably cannot do.Unlike Li-based cells, lead acid batteries are not particularly finicky about charging, not very sensitive to environmental temperatures and take considerable abuse. With low enough charge current, you don't even need a charge controller, just a blocking diode to prevent the solar panel from discharging the battery at night.

author: Zero999
author_rank: Super Contributor
timestamp: January 17, 2023, 10:24:29 am
content: Quote from: JimRemington on January 17, 2023, 05:20:38 amHow lower charging current would you deem to be safe?I've tried 14Ah batteries and found that 500mA solar panels were enough to overcharge them, which was fixed by adding a voltage regulator set to the float voltage. I think you'll need something to clamp limit the voltage, unless the batteries are very large, compared to the solar panels.

author: JimRemington
author_rank: Regular Contributor
timestamp: January 17, 2023, 05:26:30 pm
content: Some sort of charge regulator is always a good idea, but it is not absolutely necessary.QuoteDepends on the details of the project and the battery chosen. My solar car battery charger trickle charges at 50 mA.The commercial charge controller on my 600W, 500 Ah power outage backup system trickle charges at 200 mA when the system is fully charged. Both have been operating for years without any issues.