Want to run a 12v fish tank pump of solar.

[Helimadness]

Hi All.

Thanks for the replies.
First up this is just a simple project to learn a bit about Solar power and have some fun. I have always liked solar but never had a use to put it to practice.
I am fairly ok with working out the power requirement numbers for battery's panels etc.
Also I dont think the system needs to run 24 hours. One model had the pump running 15 min then 15 min off 24 hours a day, so only a total of 12 hours a day running. I am thinking if it stopped for several hours over night would also be fine. Can experiment with that and add panels / battery's if more power needed.

The bit I wasn't sure about was is it ok to run a motor straight from a solar panel. As the voltage tappers off with fading sun I assume the motor will be trying to draw more current until it gets low enough it will stall. I assume the motor will keep drawing max current until the sun gets bright enough that the voltage increases enough for it to start again. Is this really nasty for the motor and cells or will it be just fine ???

If I run a battery I assume I will need some sort of controller to limit the draw from the battery so it turns off the pump if the voltage gets too low. (Just reading about PWN and MPPT controllers after the tip below) Not sure if these controllers can control the out put of the battery or if they are meant more for controller the solar input ?

Cheers

[Sunking]

First question you need to ask yourself is why do you want to do this? If it is to save money or be GREEN forget about it as that is a BIG LIE. Anything you take off grid will cost you roughly 10 times more than buying it from the power company.

Assuming from your number of a 12 volt system to run 24 hours would require a 40 to 50 AH battery. Minimum panel wattage required is 75 watts using a PWM controller and up to 250 watts if you get less than 3 Sun Hours in winter. So do the math at a minimum you are looking at $300 for minimum setup, and up to $900 to generate 1-cent worth of electricity per day. You don't have to be an accountant to figure it the economics.

$100 of that $300 to $900 is for a two year battery you get to replace in two years. Battery cost alone is: $100 / [730 days x .1-Kwh] = $0.73/Kwh. Now go look at your electric bill and see what that mean ole greedy power company charges you for a Kwh.

So why are you wanting to do this?

[Amy@altE]

First, you need to get your units of measure right. I'm guessing is it is 12V 350mA. 12V x .35A = 4.2W pump. That is quite small. To run it 24 hours, you would need to generate 4.2Watts x 24 hours = 100.8 Watt hours to run it off the grid. To determine the size battery to run it when the sun isn't shining, .35A x 1 hour = .35Ah / 20% depth of discharge = 1.75ah 12V battery per hour. Look at the markings of the battery you have and see how many Ah it is. You can do the math to figure out how many hours you can run the pump off the battery you have, for example, 1.75ah x 24 hours = 42ah. I don't know where you are, so I don't know how much solar you would need to charge the battery.

The panels they are recommending are two 6V 520mA panels, wiring 2 in series gets you 12V 520mA. 12V x .52A = 6.24Watts. This will allow you to power your pump directly while the sun shines, it will run much slower when it is overcast, and stop when it is dark.

[Helimadness]

Hi All

First time here.
Taken on a small project of making a vertical hydroponic garden for my apartment. I will be using a small 12v 350mah DC water pump. The site I am buying from had a recommended solar package of 2 x 6v 520mah panels in series. Sounds like all should work just fine during the day. Maybe not such a big deal if it doesn't pump during the night. Still have to work that out. Figured its kinda a "green" project so making it totally self sufficient might be nice.

So my question is. Should I have some sort of voltage controller between the pump and the panels. What happens when the sun goes down and the voltage slowly drops off. Does it just take care of itself or is the amp increase as the voltage drops going to be really nasty for things. Was thinking maybe there is a low voltage cut off switch or something that you can get. Really no idea.

I also have a small sealed lead acid battery lying around. Was thinking I could use that as a buffer. Might get a few more hours out of the pump as assume the panels will charge at slightly more than the pump needs so might slowly top up the battery. Not so fussed on using the battery if I don't have to.


Cheers