# Solar->Battery->Timer->Water pump

Discussion in 'Power Electronics' started by lambert86, Sep 23, 2013.

1. ### lambert86

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Sep 23, 2013
Hi all,

This is my first post after reading through the forums for a while now. I have a couple of questions, and was hoping that someone here could help me out. My plan is to have a small solar panel charging a battery in the day time. I would like to run of of this a timer to control a pump. I was hoping to use an old windscreen washer pump but maybe thats too powerful for my purposes? Basically im trying to construct a very miniature hydroponic system for growing chillis on my windowsill. The pump will need to run about four times a day for however long it takes to fill two small pots with nutrient solution, i am thinking no more than a minute.

• So i guess my questions are, and sorry there are a few..
• What sized solar panel would be suitable?
• Would a washer jet pump be too powerful?
• Is it possible to buy dc timers? (I had a quick google but only found 12v, not sure if thats suitable?
• What voltage/amperage battery do you think i should use?

Id be very grateful to hear from anyone that could help on the subject. I was hoping to have a little volt meter somewhere so i know the battery is charging and was thinking of possibly running some fans at a later date but I understand if thats all getting a bit mental and difficult .

2. ### donkey

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56
Feb 26, 2011
ok cos everyone has answered all my solar questions I will pass on the knowledge.
1 the size of panels you need is totally dependant on your setup.. if you are using a 12volt battery than 12volt is what you need.
as for how many watts then you have to figure out how much load the battery is under (the amps of the pump in this case) then take that from your battery. so e.g. you have a 7.5ah battery and turning it on 4 times a day will drain 1 amp. now you have 6.5 amps left in your battery. lets say you get 8 hours of sun per day. well then take how much amps you need (1 in this case) and divide by 8. now multiply by 12volt to tell you how many watts is needed. personally I would go higher due to losses and ineffiecnies in panels

2 it would probably be too powerful. but it is your design. you can make it shoot the nutrient solution 100 metres through the air to the pot if you want. look at its litre per minute and calculate the best for you

yes it is possible and 12volt is fine as most solar setups are 12 or 24 volt

the battery you need is dependant on the load again. so lets say your pump takes 1 amp per minute. so 4 amps per day, lets say for safety that you go 3 days without sun to bring it to 12 amps. so you are looking at a battery with more than 12 amps, but SLA baateries hate being under 50% charge so you need to double that 12 to 24 to keep the battery usable.

I am very tired right now but hope this helps you out and I really hope I am making sense to people other than myself lol

3. ### jackorocko

1,284
1
Apr 4, 2010
You would probably need to go into detail a little more about the above load to find the answers to your other questions. if it is a 120V AC pump then I think a 12V solar panel is not going to cut it to say the least.

4. ### lambert86

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Sep 23, 2013
All makes good sense to me mate thank you very much. I wil do a bit more research and i imagine that Il have a few more questions.

Oh yes the timer, any ideas on that anybody?

5. ### lambert86

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Sep 23, 2013
Yes thank you, i understand those basics.

6. ### donkey

1,293
56
Feb 26, 2011
if you are using a mains powered pump then you can find a mains powered timer and inverter or you can use the 12volt timer before the inverter.
just check what load it carries. as for alternatives look for a 12volt pump.
depends on how much solution you need
that link shows a pump that will give 17.4 litres p/min. if that's all you need than try it out but there are others

with solar try to work backwards, decide on what is being hooked up, find its load then calculate a battery and solar panel to suit.

7. ### lambert86

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Sep 23, 2013
Ok thanks so much for your help. I have found the pump of my dreams, its 4 watts and 350ma. In total it will run 4 times a day for about 2 minutes each time. I am starting to think i wont need that big of a battery right?i work that out to about About 200Ma per day?

8. ### lambert86

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Sep 23, 2013
I may be wrong here but doing some quick numbers in my head on the train i make the required panel less that a watt? It would be great if you could confirm this.

9. ### BobK

7,682
1,688
Jan 5, 2010
Don't know how you got that figure. First of all 200mA per day is meaningless, I think you want mAH per day.

If the pump draws 350mA and is on 8 minutes per day, this is 8 / 60 * 350 = 47mAH per day. Rechargeable AA NiMH batteries (about 2000mAH) would run it for about 42 days, so you would not need much of a solar panel at all to keep it charged.

Bob

10. ### BobK

7,682
1,688
Jan 5, 2010
More calculations. Assuming the pump runs on 12V. (at 350mA that would be 4.2 Watts.)

You are using 47mAH at 12 V = 0.56 WH per day. So a 1 Watt solar panel would be enough to keep it going even if you get less than 1 Hour of sunlight per day.

Bob

11. ### lambert86

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Sep 23, 2013
Thank you thank you.
Here is my pump

I think it should be suitable? Im now looking at this 1w solar panel.
I have managed to get hold of an old 12v battery from a motorbike, (overkill perhaps?) and i plan to convert a programmable timer like this.

Any thoughts welcome and thank you again for help so far.

12. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

25,482
2,830
Jan 21, 2010
3 of those panels should provide sufficient voltage to charge the 12V battery (but I'd probably use 4). Note that you need some form of charge control (even if it's basic).

13. ### lambert86

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Sep 23, 2013
Oh right ok, il look into that then thanks.

14. ### lambert86

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Sep 23, 2013
So is this the sort of thing that you mean?
And if i get them panels il be wiring them in series right? Perhaps just easier to get one larger one?

15. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

25,482
2,830
Jan 21, 2010
What you really want is a panel rated at between 16V and maybe 24V, and at a low current. Typically these are sold as "12V panels".

It would be best to get a built up panel that is protected from the weather if you plan on placing this outdoors.

I have a small 5W panel that is about 35cm x 25cm, and I've not seen anything commercial that is a lower wattage.

OK, that link finally opened. I see you're talking about a charge controller.

That would work, however it may be way over the top.

In your case, if your panel is rated for a very low power, and your battery is a lead acid type, then you can get away with a simple zener diode and blocking diode combination.

Check the battery to find out what the maximum float charge it allows. Let's assume that is 13.6V.

I would get a zener diode rated at twice the panel wattage, and a voltage as close as possible to this. (Don't go too far over, 14V may be OK)

Then use a circuit like this:

D1 is a normal rectifier diode. In your case a 1N4001 would be fine (certainly for any panel rated under 12W)

ZD1 is the Zener diode 14V 10W perhaps?

The charge controller you linked to does a lot more than this. It will also disconnect your battery from the load if the charge level falls too far (for one thing), and charging is likely to be done more efficiently in marginal conditions.

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