Help with solar fountain design

Thread Starter


Joined Jul 2, 2023

Im a complete novice here, very new! My history is Im a paramedic but recently diagnosed with autism (lots of social issues for me!). But I often get an intense interest in certain areas (autism!). What I really want to do is try and build a few low voltage electronic circuits.

1/ A solar water fountain with battery backup/charging. Can I find anywhere an article of a circuit design! I dont really want to buy one from amazon, I want to try and build my own. To me, it shouldnt be overly difficult though as it perhaps replicates solar circuits with batteries. I want a bigger type solar panel though, I had a 5w Amazon one, but I think the battery was rubbish, I tried to reverse engineer it, but got to the battery and didnt want to cut, Im assuming thats where the circuit was. My 5w one often didnt keep running, maybe the battery was a low mAh one, who knows. My theory is that a bigger panel will gain the charge to keep something smaller like my pump running. Plus I thought if I got a bigger MaH battery itt would help? Maybe like 5000MaH or bigger???? I guess you need a charge controller, an optical diode for detecting light (I forget the technical term!). Can anyone help, I've honestly tried to research it, but get confused with resistor values etc, I've probably spent 10+ hours with no luck - its all geared towards solar! I'll try and include my pic of my previous solar panel pack. The pump stopped in the end, hence trying to build my own with replaceable parts.

2/ Was going to be about solar lights, but maybe another time!


Rik G - Norwich!



Joined Oct 2, 2009
Welcome to AAC!

Firstly, you need to conduct an energy budget. In other words, make sure that the energy input exceeds the energy consumed by a sufficient margin to account for low input occasions.

Pump motor energy requirements: 2.5W @ 9V
This translates to about 0.3A @ 9V
If the pump has to run for 24 hours, this is 7.2Ah or 7200mAh.

Next we look at the battery specs.
Battery: 1500mAh @ 7.4V
The battery is grossly under power for this application.
You would be better to use a 12V SLAB (sealed lead-acid battery) with at least 7000mAh capacity.

(We can revise our analysis if we assume that the battery only needs to supply power for 12 hours when the sun goes down.)

Next, we can analyze the solar panel requirements if it has to power the pump as well as charge the battery.
We have to derate the solar panel to take into account efficiency losses.
We also have to derate the solar panel to take into account cloudy days.

Hope this provides enough information to give you a starting point.


Joined Aug 7, 2020
What do you want it to do?
i.e. when the sun stops shining, you obviously want the fountain to continue to work, but for how long? Until it gets dark? Until the battery goes flat?
For a very simple solution, connect a 12V solar panel directly to a 12V sealed lead-acid battery.
Use a simple comparator circuit - when the voltage exceeds 14.4V turn the pump on, when it drops below 13.5V turn it off.
The pump is acting as a charge controller to prevent the battery overcharging.


Joined Jan 23, 2018
The very simplest option could be a starter setup where the fountain was supplied power by the sun. Just a solar electric array sized to be able to power the pump when there is about half the maximum available sunlight. Since not many folks look at a fountain in the dark that would be reasonable, and it will allow experimenting and learning. Also it will allow for future additions, without needing to replace any parts.
THEN, if the TS decides to extend the running time, there will be a functioning system to add onto, so diagnotics of any problems will cover a smaller segment.