Simple Solar Powered Pump w/ Rechargeable Battery

Thread Starter

electricjack

Joined May 14, 2020
5
Hi Everyone,


My aim is to build a simple solar powered pump with a rechargeable battery to water plants. The idea is to use a 6V 1W Solar Panel connected to a TP4056 (protected) to charge a 18650 Lithium Ion Battery. On the output is an MT3608 2A Boost Converter to step up the voltage to a 3V/6V DC Pump.

I would like to know if the design work and any correction/ improvements on different components or adding in a timing function for the motor.

I have attached a diagram for more information. I am a total beginner and would really appreciate any help or advice.


Many thanks,

Jack
 

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Papabravo

Joined Feb 24, 2006
14,452
The running current of the motor is one thing, but the startup current is something else again. SMPS (Switch Mode Power Supplies) are notoriouly awful when it comes to dealing with load transients, like taking a motor from zero to running speed. The current demand could be 2 to 4 times the running current. I would spend some time experimenting with and characterizing the motor. That way it won't be a surprise.
 
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Thread Starter

electricjack

Joined May 14, 2020
5
The running current of the motor is one thing, but the startup current is something else again. SMPS (Switch Mode Power Supplies) are notoriouly awful when it comes to dealing with load transients, like taking a motor from zero to running speed. The current demand could be 2 to 4 time the running current. I would spend some time experimenting with and characterizing the motor. That way it won't be a surprise.
Thank you for the quick response, I had never considered the startup current required to get the motor running. I've ordered the components so I will do some experimenting when they arrive. Do you think the 6V 1W Solar Panel will provide enough power to charge the 18650 Lithium Ion Battery and power the 3/6V DC Motor?
 

Papabravo

Joined Feb 24, 2006
14,452
Thank you for the quick response, I had never considered the startup current required to get the motor running. I've ordered the components so I will do some experimenting when they arrive. Do you think the 6V 1W Solar Panel will provide enough power to charge the 18650 Lithium Ion Battery and power the 3/6V DC Motor?
6V @ 1W would be 167 mA. You should be able to compute the charging time for your battery at that current. If you can't compute it then you can measure it. It might be 2 days for all I know.
 

nsaspook

Joined Aug 27, 2009
7,595
The running current of the motor is one thing, but the startup current is something else again. SMPS (Switch Mode Power Supplies) are notoriouly awful when it comes to dealing with load transients, like taking a motor from zero to running speed. The current demand could be 2 to 4 times the running current. I would spend some time experimenting with and characterizing the motor. That way it won't be a surprise.
I've found you must really look hard for the type of overcurrent protection in a SMPS. If it says hiccup mode (most are) you most likely are screwed driving high power motors or MPPT type high power battery charging applications directly from the power supply. ‘Constant Current Limiting’ or resettable 'foldback current-limiting' mode is what you want.

https://www.analog.com/en/analog-dialogue/articles/preventing-start-up-issues-due-to-output-inrush-in-switching-converters.html
 

dendad

Joined Feb 20, 2016
3,602
Why not just run the pump from a larger solar panel, with voltage limiting if needed, and just forget about the battery? Then the pump only runs during the day.
But really, the first thing you need to do is to hook the pump up to a power supply and test to see what voltage and current you need for it to work.
Otherwise, you are just trying to design for unknown conditions.
 

MisterBill2

Joined Jan 23, 2018
7,040
DD has it! First you must decide how long you want to run the pump, and then see how much power, (volts and amps) the pump requires to run. That will tell you the size of battery that you need to provide that much power. Then you can research and determine how much solar cell you need to charge the battery.

Reality is that the McGyver method of ignoring the numbers only works on TV, but in real life the numbers need to be considered.
 

Thread Starter

electricjack

Joined May 14, 2020
5
Why not just run the pump from a larger solar panel, with voltage limiting if needed, and just forget about the battery? Then the pump only runs during the day.
But really, the first thing you need to do is to hook the pump up to a power supply and test to see what voltage and current you need for it to work.
Otherwise, you are just trying to design for unknown conditions.
That's a good idea, I agree that the design would work better if the design is kept simple. However, my aim is to make it compact and portable which eliminates large solar panels. This is the pump that I am thinking about using:

https://www.ebay.co.uk/itm/Mini-Micro-Submersible-Water-Motor-Pump-New-DC-3-6V-120L-H-Low-Noise-UK-Stock/201497218766?hash=item2eea2b8ece:g:BLMAAOSwZG9WjCqA

If you don't mind me asking, what are your thoughts on the "Irrigatia" systems. They seem to do the trick and utilise small solar panels:

https://www.irrigatia.com/irrigation-kits/sol-c12

Thanks for the help!
 

Thread Starter

electricjack

Joined May 14, 2020
5
DD has it! First you must decide how long you want to run the pump, and then see how much power, (volts and amps) the pump requires to run. That will tell you the size of battery that you need to provide that much power. Then you can research and determine how much solar cell you need to charge the battery.

Reality is that the McGyver method of ignoring the numbers only works on TV, but in real life the numbers need to be considered.
You are right, I do need to do the math to calculate the size of the solar panel. Do you know how this model of solar irrigation manages to achieve the task with such a small solar panel?

https://www.irrigatia.com/irrigation-kits/sol-c12
 

Thread Starter

electricjack

Joined May 14, 2020
5
I've found you must really look hard for the type of overcurrent protection in a SMPS. If it says hiccup mode (most are) you most likely are screwed driving high power motors or MPPT type high power battery charging applications directly from the power supply. ‘Constant Current Limiting’ or resettable 'foldback current-limiting' mode is what you want.

https://www.analog.com/en/analog-dialogue/articles/preventing-start-up-issues-due-to-output-inrush-in-switching-converters.html
Thank you, I will follow the link and do some research. I don't think the TP4056 is as good as it looks when used for this function.
 

CRYPTOCOM

Joined Dec 17, 2012
1
Thank you, I will follow the link and do some research. I don't think the TP4056 is as good as it looks when used for this function.
So, what exactly is this pump used for?

Portable. Suggests: Differing loads, place to place. Assuming you're familiar with pump curves, the head & hydraulic resistance you're pumping against is critical to calc'g current draw and volume flow.

electricjack, you have some work to do....
 

Bernard

Joined Aug 7, 2008
5,656
In comparison with other pumps, your pump might draw about 600 mA under load or 3.6 W.
If pump is operated at 25% duty cycle then solar panel might almost keep up. Real measurements
are better. More information on project is also better.
 

Bernard

Joined Aug 7, 2008
5,656
Similar boost converters show maximum output current only at maximum input V; 3V in 5V out @ 300mA, 24 V in, 12 V out @ 1700 mA. Or, 4.2 V in, out 12V @700 mA, 30V in, 12 V out @ 3.3 A.
 

MisterBill2

Joined Jan 23, 2018
7,040
Similar boost converters show maximum output current only at maximum input V; 3V in 5V out @ 300mA, 24 V in, 12 V out @ 1700 mA. Or, 4.2 V in, out 12V @700 mA, 30V in, 12 V out @ 3.3 A.
At all times and under all conditions a boost converter is less than 100% efficient. That means less power out than power in. So choosing components to work at available voltages is a better choice. OR changing the voltage supply to match the load, as in adding more solar cells.
 

Papabravo

Joined Feb 24, 2006
14,452
At all times and under all conditions a boost converter is less than 100% efficient. That means less power out than power in. So choosing components to work at available voltages is a better choice. OR changing the voltage supply to match the load, as in adding more solar cells.
Sometimes they are MUCH less efficient than 100%. Especially when trying to adjust quickly.
 

MisterBill2

Joined Jan 23, 2018
7,040
My point about boost converters is that they are seldom of benefit in systems with limited power availability, since they never result in an increase of power. It is far better to match the voltage requirements of the user side with the source side by selecting the correct components. That could mean adding more batteries of more solar cells or finding a different voltage pump motor.
 

Bernard

Joined Aug 7, 2008
5,656
My MT3608 boost converter with 3 V input powered a maximum load of 20 ohms & with 4.5 V,
load increased to 10 ohms.
Driving a 4 W ? load with 1 W is not a great idea but can be done, possibly by charging a large cap. from SP & dumping it into pump. I have used this idea to supply starting current while SP supplied running current.
 
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