7v Solar Pump - Using a solar regulator and batteries to recharge

[burgo855]

So i got a really cheap small pump that i am using for a project at home, it moves a very small amount of water(160L/H) at a time but it is the perfect item i wanted for my project. The pump came with a solar panel, and it was designed to plug the solar panel directly into the pump and providing i have sun "voila" the pump moves water. Its a cheap piece of china but its what i need.

So it works well, but i want to change from only working under direct solar to using rechargeable batteries along with the solar panel.

So my pump is: 7V, 1.2W, working current 150MA.


I was thinking of using 2 x 9V rechargeable batteries because they produce less oomph/MA than your AA's as the pump is not a big power consumer i thought although the pump is designed for 7V i don't think a 9V battery would hurt it?

I was thinking of getting two of these: and connect them in parallel?

And then i was thinking of getting this regulator:

to control the MPPT.

I'm a newbie when it comes to solar, but I have no issues with soldering it all up and sealing it all up in a custom box of some sort. Just curious if this is frowned upon?

Also if i got all of the above, should i just wire the batteries parallel and then wire the solar panel to the regulator board and the parallel batteries and then run the pump directly off the batteries? I can get a much better quality 12v regulator board which will then support the input of solar, batteries and output for a device but its too much overkill i don't need something that big.

Any ideas out there?

[Mike90250]

First lesson of marketing. Never include a PV panel larger than you need.

The "included" panel can barely power the pump. It has no hope of powering the pump AND recharging a battery.

Now your first lesson of electricity, Amps and amp hours
Your pump is 0.150 Amps (150mA)
In two hours, it will consume 300mA hour
How many hours do you need it to run?
how much PV panel do you need to replace the mAh used & to run the pump for the 5 good solar hours in a day?

[burgo855]

So if i were to try use the original solar panel to charge the batteries it would fail to charge the batteries as it was made for only a 7v pump? I want to run this for as long as possible everyday.

so more or less 24 hours, so i want to get as much solar charge as i can to charge those batteries up for the night.

So i need: 150mA x 24H = 3,600mA, do i need to subtract 12 hours here as the batteries should run when the sun is out?

I guess this means i will need more like 12v and then reduce its voltage down to the pump?

Guess i need a new panel to begin with and then i still need to work out what batteries/voltage and a different regulator.

What do you recommend Mike?

[Mike90250]

> So i need: 150mA x 24H = 3,600mA, do i need to subtract 12 hours here as the batteries should run when the sun is out?

sort of . You need 3600mAh to run for 24 hrs. Your solar panel had to harvest that, plus another 50% to account for losses, all in about 2-4 hours. (if we know your location zip code, we can look up your shortest day sun hours) 3600 x 1.5 = 5400maH
We need a 12V battery, and also an efficient DC-Dc down convertor to your 7V

Now the choices begin, The "right size battery" would be about 20ah, about the size of a garden tractor battery.. But those are not in mass production and are not cheap
12V marine/deepcyle batteries are much larger, about 90ah and likely only cost a little bit more - about $100
That size battery could use a 100w PV panel and a 10Amp PWM charge controller to keep it happy, But this is way overllkill then the "right" size battery and panel, but are in mass production and cheap. Small and expensive? Larger and cheap ?

[PNPmacnab]

Interesting board, I haven't seen that board before. Looked on ebay and the description is pretty sketchy. The MPPT pot is probably just setting the input power point voltage with no tracking.. That is generally good enough. You should get an Arduino micro controller to control when the pump runs, from what source and disconnects when battery is low.

Can you give a link to that listing please? There is a bit of it I would like to study.

[PNPmacnab]

Just search "MPPT board" price + shipping first and they will pop up. As they say, something was lost in translation. Pretty hard to piece together the technical facts. Another board that pops up with similar explanations is one with the BQ24650 chip. That chip is listed as MPPT but it doesn't track with current + output voltage, rather the temperature of the panel and panel voltage. Note there is no connection for a temperature sensor. So, this has a fixed voltage power point. That gets you 90% there. I do that with the cheap buck converters. Add external panel voltage monitoring, fake out the feedback, and keep the panel at a fixed voltage. Likewise with brushed DC motors these buck converters can turn into Linear Current Boosters for battery-less pumping systems.