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The electronics for powering a pump via solar power Answered

So I've been tossing around the idea of making a automated garden that uses solar panels, much inspired by a vermiponics instructable I saw but I have some questions of theory and practice I'd like help with before I go into it. I've worked with simple electronics and have a fairly good grasp on the theory but nothing quite this complex or with components I'm not familiar with, so I'm looking for advice.

1) Solar panels must need something like a capacitor or battery to store the energy for the motor to use, and how would I get this reservoir to trigger at a high enough voltage so that the motor can actually spin and I don't just end up with a motor charging a battery that is discharging across a motor at a low enough current that it doesn't spin.

2) preventing the battery from discharging back into the panel, I assume one would use a diode for this but I'm curious if there's anything additional that is required

3) If I wanted to try adding further automation by adding an arduino with a mess of sensors, would powering the arduino from an additional battery charged by the same panel work (I assume this would slow down the charging of the motor's battery).

4)  Safety features to implement so I don't do things like overcharge the batteries/ suggestions encouraged.

The arduino is currently gravy for the project, worst comes to worst I can set up some simple level switches.

Discussions

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dudes

3 years ago

A few questions before I try to help;

1. What is the scale of this project? What size pump, solar panels, batteries?

2. I had another question, but I just forgot it...

I guess that's it for now.

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squirrelchaserdudes

Reply 3 years ago

Scale of the project currently is about one or two bins of soil and gravel perhaps, with a reservoir the water would drip into. Not a full fledged green house. Mostly attempting to test if an autonomously powered and smart plant growing system would work. (ergo why the arduino is needed to gather data like moisture).

Panels I'm thinking of are somewhere in the 5W range (around what is in those solar car battery chargers) I am a complete noob to solar so I don't quite have a feel for the scale.

I'm looking to run something like a little 12V pump which is what I currently have. Its rated for 240L/hr (or 4L/minute) with a head of 3 meters

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dudessquirrelchaser

Reply 3 years ago

Ok cool, I'll try to answer a few questions for you.

1) Yes, you would need a battery (a capacitor would not work). I would suggest a small (maybe 5-15Ah) 12v sealed lead acid battery. This size would work well with the 5W solar panel and pump.

2) You are correct, a diode is needed to prevent the battery from discharging through the solar panel. Just a diode. You have a 5W panel, so I'm guessing it's 12v, which means peak current is about 420mA, so just about any diode you can find would work. But if you want maximum efficiency, you should use a Schottky diode, rated for at least 1A.

3) You wouldn't actually need a separate battery for the Arduino. Since it runs off 5v and the battery would never dip below 10v (if properly cared for), you could just use a high-efficiency buck converter to get the 5v. They're pretty cheap on Ebay or Amazon.

4) Overcharging: With a 5W solar panel, there really isn't any chance of overcharging the battery. You could simply wire the panel directly to the battery through the diode and it would be fine. However, if you're worried about it, you could use a cheap solar regulator, or simply have to Arduino protect it. (If you want some ideas for that, I'll be glad to help)

Over-discharging: Simply having the Arduino monitor the battery's voltage and shut off the motor if it gets too low would suffice. Using a 3:1 voltage divider would allow the Arduino to read up to 15v, thus allowing it to easily monitor the 12v battery. Controlling the pump through a mosfet would allow you to turn it off if the voltage ever got too low (below 10v would be good).

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squirrelchaserdudes

Reply 3 years ago

The panel I'm looking at produces a max of 18V which is charging a 12V battery and this I imagine would be problematic. So I'd probably need some kind solar regulator or maybe find a way to get a read on the voltage between the battery's terminals and cut off the panel if its at 12V.

https://www.amazon.ca/ALLPOWERS-Maintainer-Automob...

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squirrelchasersquirrelchaser

Reply 3 years ago

Luckily though the panel has an in built diode, but I may try swapping that with the more efficient one you suggested.

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dudessquirrelchaser

Reply 3 years ago

The panel you linked, assuming that is the one you intend to use, is actually perfect for this application. Despite it's rated voltage of 18v, it has low enough current that it will never bring the battery's voltage above 13 or 14 volts, which is still safe. So you could just connect it directly to the battery and be fine, as long as the battery is above half a dozen amp hours in size. If you want to use a regulator, just in case, there are a few options;

1. Buy a buck converter or solar charge controller, the latter would cost a whole lot more and not really have any benefit at this scale.

2. Make a voltage converter. A buck type would be better, but much, much harder, while a linear would be easy, cheap, but not ideal. It would however work well enough for this application. Check out the LM317T voltage regulator, that could be used to make a 13.5v regulator, which would keep the battery 100% safe. I attached a basic voltage regulator circuit below.

3. Connect the solar panel to the battery through a mosfet, allowing the Arduino to disconnect it if the battery voltage went too high. Ideally, you would want to use a logic-level p-channel mosfet. Check the pictures below for the basic schematic.

4. If you want really basic and really cheap, a 13.5 (or close) volt zener diode would make a simple voltage regulator. Not a very efficient one though.

As for the diode, the one the solar panel comes with is probably efficient enough. A regular diode has a forward voltage drop of about 1v, while the Schottky diode I mentioned earlier has a drop of about .4v. So at .3 amps (about the max the solar panel could output), a Standard diode would lose about .3W (1v x .3A), while a Schottky diode would lose about .12W (.4v x .3A) So there really isn't much benefit, a gain of .18W maximum, the normal gain would probably be able .05W, almost negligible. I would just use the diode it comes with.

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dudesdudes

Reply 3 years ago

I totally forgot to attach the images, here they are;

20160325_144751.jpg20160317_222852.jpg
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dudesdudes

Reply 3 years ago

ignore that second one, it's the wrong image XD here's the right one;

20160325_150822.jpg
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squirrelchaserdudes

Reply 3 years ago

And I assume the arduino should be able to handle 13.5 Volts (which it seems this battery won't really get to.

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dudessquirrelchaser

Reply 3 years ago

Yes, the on board regulator can safely work with 13.5v, just make sure to connect the battery to the DC input jack or the VIN pin, don't connect it to the VCC pin or it'll kill the Arduino. For the monitoring of the battery voltage, use a 3 to 1 voltage divider by connecting a 20k ohm resistor to the battery, a 10k ohm resistor to the ground, and measuring the voltage where the two resistors meet (you'll see what I mean in the picture I previously posted) That way you'll be able to measure up to 15v with the Arduino's ADC. Just remember, whatever the Arduino reads is actually one third of the actual voltage. So if it reads 4v, the battery's voltage is actually 12v.

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gmoonJonathanrjpereira

Reply 3 years ago

Not sure that's exactly what the OP was looking for...but that's a pretty sweet I'ble. 3D illustrations, good photos, goals nicely discussed.

Well done. Favorite-ed. The link doesn't work for me, btw.

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Josehf Murchison

3 years ago

I have done this before.

1. You should only water your garden at night or you can cook your plants from the sun. Use the solar panels to charge the batteries through a charging circuit during the day and a timer to turn on the pump at night. You shouldn't need to run the pump for more than an hour if you have a good pump.

2. All you need is a diode to prevent the solar panel from draining the battery after dark or damaging the panels.

3. Arduino would be good for the timer and monitoring the charging of the battery, you can add a moisture sensor so it will only water the plants when they need it. Over watering the plants will kill the plants and some plants need more water than others.

4. A charging circuit is a must or you can over charge the batteries.

For this type of a system to work, the most important thing to look at is the sun.

Where I live some months I get only 55 hours full sun a month.

For a solar system to work with any reliability you need about 150 hours a month.

Then figure out how many watt hours you need to run your system a month.

You get 1 watt hour for every hour and every watt your solar cell is, while it is in the sun. So 1 watt solar cell in full sun for 1 hour is 1 watt hour.

These systems most of the time are 50% efficiency.

And then do the math.