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

[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

[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.

[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?

[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

[Amy@altE]

There are DC pumps specifically designed to work off solar panels. Laing, El Sid / March come to mind. They are about $200, not sure if that's out of your budget, it may be overkill. My gut says the DC pump you have in mind should be ok to run off solar direct, especially since the manufacturer is specifying what size panel to use. It might have a little difficulty starting up in the morning when the sun is low, it needs a good boost to start (don't we all).

To run off the battery, the motor is small enough that it will just draw what power it needs from the battery, so it will be on full or off. You can get a DC timer to control it, like the FlexCharge Timer to turn it of and on, but I think that one just has 8 events (on/off). I think we calculated 1.75Ah per hour, so 12 hours would need 21 Ah battery.

An MPPT charge controller is way overkill for what you need. A PWM will be just fine.

.35A motor x 12V = 4.2W x 12 hours = 50.4Wh. Still don't know where you are, so I'll assume the worst, 2 sun hours (OK, that's not the absolute worst, but close enough). 50.4Wh / 2 sun hours / .67 inefficiencies = 37.6W solar panel. Round up to 40W. A 40W panel has a short circuit current of 2.54AIsc x 1.25 NEC requirement = 3.17A minimum size charge controller. The Morningstar SunGuard 4.5A charge controller would do the trick.

[Amy@altE]

I'm changing my mind on the charge controller. You shgould get one with Low Voltage Disconnect, so if the battery is low, the pump will turn off. Morningstar SS-6L-12V SunSaver 6A.

[paulcheung]

It is bad idea to run the pump on and off if fishes are in there, the water will get green and dirty and the fishes will get sick. The pump is supply the oxygen and filtering the water, try not turn it off.

[Helimadness]

There are DC pumps specifically designed to work off solar panels. Laing, El Sid / March come to mind. They are about $200, not sure if that's out of your budget, it may be overkill. My gut says the DC pump you have in mind should be ok to run off solar direct, especially since the manufacturer is specifying what size panel to use. It might have a little difficulty starting up in the morning when the sun is low, it needs a good boost to start (don't we all).

To run off the battery, the motor is small enough that it will just draw what power it needs from the battery, so it will be on full or off. You can get a DC timer to control it, like the FlexCharge Timer to turn it of and on, but I think that one just has 8 events (on/off). I think we calculated 1.75Ah per hour, so 12 hours would need 21 Ah battery.

An MPPT charge controller is way overkill for what you need. A PWM will be just fine.

.35A motor x 12V = 4.2W x 12 hours = 50.4Wh. Still don't know where you are, so I'll assume the worst, 2 sun hours (OK, that's not the absolute worst, but close enough). 50.4Wh / 2 sun hours / .67 inefficiencies = 37.6W solar panel. Round up to 40W. A 40W panel has a short circuit current of 2.54AIsc x 1.25 NEC requirement = 3.17A minimum size charge controller. The Morningstar SunGuard 4.5A charge controller would do the trick.

Thanks for the detailed reply. Sorry if I didn't mention before, I am living in China at the moment. Qingdao so about 36 deg north. Sun rise 7:08 am set 5:11 Pm, So about 10 hours. biggest variable on that would be the pollution. Kinda sucks some days. Will be interesting to see the performance difference between a clear day and a full smog day. Certainly highlights the need for better energy and life style living here. The documentary on vertical hydroponic farms really caught my attention on the plane back from xmas holidays. Hence the round about way of ending up here. Sorry off topic.

Most of that above makes sense. To start with I think Im going to run with what I have and go from there. Not really keen on introducing a large battery. Like pointed out before maybe just better to plug into grid. I have an adjustable power supply so can test the min voltage required for it to kick in.
I do have fairly good access to cheap electronics. Browsing around I found this PWM charger and a Battery low voltage cut off for only a couple of bucks each. Sorry all in Chinese, google chrome translates it
Was thinking could use the battery low voltage cut off directly on the solar panels. Its adjustable I think so can just set the panel cut off to match the lower limit for the pump. Not sure if the panels mind having the load cut on and off like that?

http://item.taobao.com/item.htm?spm=a1z09.2.9.81.NaDWTB&id=12898275714&_u=jpoj6se0436

http://item.taobao.com/item.htm?spm=a1z09.2.9.92.NaDWTB&id=19342076310&_u=jpoj6se0dd9

One thing I dont understand about the above it the short circuit current of the panels. Is that the maximum current they can provide? So need a controller above that ??

Paulcheung, as for the fish, there isn't any. The fish pump I am going to use for an indoor hydroponic vertical tower. So just needs a small flow of water to the top where it rains down over the plant roots. The water system is totally enclosed and out of light so slime doesn't grow. The plants are suspended in a mesh basket with some moisture retaining medium supporting them so having water flow 100% of the time I dont think is critical. Still a lot to learn there as well. There is Aquaponics that use fish for nutrients but thats too big a setup for my apartment.

That brings up another question. How do solar panels handle light from light bulbs? As this is an indoor system when the sun goes down the house lights are on till we go to bed. Maybe that will add some power to the system also?

Cheers

[Mike90250]

...
That brings up another question. How do solar panels handle light from light bulbs? As this is an indoor system when the sun goes down the house lights are on till we go to bed. Maybe that will add some power to the system also? Cheers

Poorly. About 10% of nameplate if you are lucky, is my guess.

[russ]

Poorly. About 10% of nameplate if you are lucky, is my guess.

Already one is dealing with something in the 15% efficiency range - now you make that 1.5% efficient = useless.

[Helimadness]

Already one is dealing with something in the 15% efficiency range - now you make that 1.5% efficient = useless.

Ok so light indoors = useless got. But where do you get the starting rage at 15% ?

Sorry might be a dumb question but first time playing with solar.

Cheers

[russ]

Ok so light indoors = useless got. But where do you get the starting rage at 15% ?

Sorry might be a dumb question but first time playing with solar.

Cheers

Solar panels vary in efficiency from maybe 10% for thin film to 20% for the higher efficiency panels for residential use.

For NASA and the military the efficiency can reach 43% though for a high cost.

[Amy@altE]

Isc is the max current output under Standard Test Conditions (STC) without a load on it. You want to use that x 1.25 to determine the size charge controller you need. You can go bigger, but not smaller.

The number of hours you use to calculate output are number that equals the output of STC, not the number of hours the sun is up. As you know, the sun is much brighter at noon as it is at sunrise, so not all hours are equal. In Qingdoa, that ranges from 4.23 - 5.55 sun hours. It takes local weather conditions into account, but that's a good question about pollution, I wonder if it accounts for that as well. http://solarelectricityhandbook.com/...rradiance.html

[SunEagle]

I'm changing my mind on the charge controller. You shgould get one with Low Voltage Disconnect, so if the battery is low, the pump will turn off. Morningstar SS-6L-12V SunSaver 6A.

Amy

Please clarify your statement about the Morningstar SS-6L-12V CC being able to turn off a pump if the battery is low.

From what I have read that can happen only if the pump is connected to the "load terminals" not if the load is connected to the battery.

While the manual does not give a maximum amp or watt rating for the "load terminals", it does warn that you should never wire an AC inverter to those terminals which could easily overload the output which suggests only a minimal load is allowed.

Do you have any additional data on the maximum size "load" that can be connected to the "load terminals"?

[Amy@altE]

He said in the OP that it is a DC pump, therefore no inverter and he should connect it to the Load connection on the controller. I believe the LVD current limit is the same as the solar limit. Checking manual to confirm.