Low Power BareBones DIY Solar controller - Page 1
Forum section: electronics / beginners

author: andrewTK
author_rank: Newbie
timestamp: January 28, 2020, 01:09:07 am
content: I am creating an auto watering system for a garden. Using ESP32, 3 12v Solenoids, 5 relays, and small dc motor (running for about 15 seconds everyday) and the solenoids and relays running for about 20 minutes everyday (worst case scenario). I have a large deep cycle marine battery, and am planning to use a 10w to 25w solar panel. My question is, are solar controllers I can buy going to use up the same or more energy than the solar panel can produce at this low power/relatively large load operation. More importantly, is there a low power way to control this if I know I'm just using this for 4 months? Power is not applicable, this needs to be "off-grid." What would very basic circuitry look like, someone suggested just using a diode for reverse charge during the night, but that seems a little too simplistic as theres no overcharge protection? Most seem to use linear converters for cost, however wouldn't it be more efficient to use buck converters, if cost is not the big issue?p.s. Let me know if this needs to be in the projects area, but I feel fairly noobish, so here I am!

author: pcmad
author_rank: Regular Contributor
timestamp: January 31, 2020, 01:54:24 am
content: why not just use a Schottky diode

author: Jwillis
author_rank: Super Contributor
timestamp: January 31, 2020, 04:58:00 am
content: Charge controller will never produce more energy than it receives. A 25W panel at 12 V will produce 2.08 Amps.First you need to know is the power requirements all your solenoids , the ESP32 , the DC motor under load and the relays .The ESP 32 operating requirements are .5 amps that leaves you with 1.5 amps to run the solenoids relays and motor.If you exceed the 2 Amps of the solar panel the battery won't recharge fast enough to keep up with consumption.

author: SmallCog
author_rank: Frequent Contributor
timestamp: January 31, 2020, 09:40:41 am
content: My letterbox has a 5W solar panel attached to a 6A PWM controller with a 7Ah battery. The controller keeps the (relatively small) battery charged from the baby sized panel without any issues. What it’s powering is a discussion for a different thread...We also have lots of solar powered sites that I take care of at work. These typically have about an 18Ah battery with 20-30W panels and either 6 or 10 amp controllers.Further to that my work vehicle will often spend weeks at a time without being used, but it has parasitic loads from the alarm system, satellite tracking, etc. it’s got a 20W panel on the roof rack wired up to a 10A controller to keep the battery topped up.I’ll leave it up to you to do the math on your consumption vs hours of sunlight but I wouldn’t hesitate to use a commercial regulator.

author: Jwillis
author_rank: Super Contributor
timestamp: January 31, 2020, 07:27:36 pm
content: Quote from: SmallCog on January 31, 2020, 09:40:41 amHours of sun is a big issue. I keep thinking of being way up here in the North . andrewTK is in the States and he only needs 20min of consumption per day . Rethinking things he could pull it off with what he has and as SmallCog suggests with a low watt PWM controller.A diode could work as long as long as the panel gives more than 12 volts on load. The panel should actually deliver 14 volts but you never know.

author: andrewTK
author_rank: Newbie
timestamp: February 06, 2020, 03:30:40 am
content: Thanks for all the suggestions! the controller I bought for 10 usd on amazon uses all linear regulators, which I wasn't a fan of since holding youre hand to it you can FEEL (heat) the energy that was being wasted. I have been looking into smaller PWM Controllers and they all seem to have much better satisfaction than the linear controllers.

author: paulca
author_rank: Super Contributor
timestamp: February 07, 2020, 01:15:47 pm
content: Basic finger in the air sizing/scaling for solar applications is:Calculate your total load over a day, then divide it to get the average watts. Multiply that wattage by 10. This is your panel size.As an example if you have a load that runs at 100W for 30 minutes every hour, 24/7 then your average load is 50W. You would look for a 500W panel(s).For battery size it depends on your location, how sunny it is and the location of the solar panel, but for the UK I try and aim for at least a week of intermittency to cover. So for the above example 50W for a week is about 8.4kWh of battery pack ( about 9 100Ah marine lead acids!).On change controllers I use an EPEver 10A MPPT controller on my 50W panel and it consumes (along with an ESP8266 monitor sending data every 5 seconds) about 50mA. the charge controller itself draws about 30mA during the day and drop to 20mA or less when it goes into night mode. So when it's connected to a 100Ah marine battery it will run for about at least a month with no sunlight.As a last resort, if mains power is available, you can connect a charger to the lead acid while it's connected to the charge controller and it shouldn't upset it. You can tigger this on a relay based on the battery voltage.