12 volt solar question

[gundownunder]

Is there somebody on here with a bit of solar knowledge that can help me out.
I'm setting up a hydroponic bucket gardening system and want to automate the watering system.
I've ordered a 12 volt, 5 watt water pump which is supposed to be solar compatible, but it doesn't say what size panel it should be plugged into.
Should I be ordering a 5w panel or do I need a bigger panel to compensate for power drop in the cables, etc. Lead from panel to pump is 5 foot long.

[AJMD429]

Dunno, but remember electricity flow backwards in the southern hemisphere....

Someone who actually knows something will soon give a better answer....

[Trailboss]

Bob,

Would it make sense to run the pump off a deep cycle battery and then charge the battery when the sun is out? This would allow you to time the watering whether the sun is out or not. If the solar panel is not keeping up with recharging the drain in battery, you can daisy chain another into the charging loop.

[piller]

Putting the chargers in parallel would allow you to charge the deep cycle battery if one solar cell is not enough. Putting them in series would give too high of voltage. I don't know your level of knowledge, so I apologize if you already know this.

If you are able to catch the Doc's joke, you surely know that electrons do NOT flow from positive to negative in the Southern hemisphere. Why, that would mean that corrosion protection would require a sacrificial Cathode. I can imagine that would mean using a huge gold plated well head and replacing it annually. Nope! Not gonna happen.

[Rusty]

I've been watching a few Youtube videos about people that are now living in RVs. One thing they like to do is achieve the ability to what they call BOONDOCKING. That means living without the support of power or water hook ups. The big investment seems to be solar energy. One of the things most people seem to be going to is lithium batteries. The lithium batteries seem to have the ability to be brought down to almost no charge at all and still charged to the top and live. A lead acid battery on the other hand will die quickly if drawn down below 50% from what I understand. Check with experts in your area.
God Bless

[Blaine]

I have one of their panels on my camper that charges two AMG batteries. I keep the electric fridge, and an electric vent on low all the time, and it runs a night light and my CPAP all night. In the morning the system only needs an hour or so in the sun to be 100%. The key seems to be a controller that will charge at a high enough voltage to max out the batteries.
Talk with these guys...Made in the USA and they have a good reputation.
https://www.zampsolar.com/

[gundownunder]

The problem with using a battery is that the system will run a lot longer. I was hoping to use just the solar panel so that the water only runs for the 5 - 6 hours a day that the sun is shining on the panel. My gardening system doesn't need water all day or even every day, as it is a double bucket system with a water reservoir in the bottom bucket.
The reason this system works so well is because we are down under, so the water flows from the bottom bucket back up into the top bucket and onto the plants

[Pop Watts]

Hi Mate.
You cannot run a solar panel directly onto a 12v pump. You need to run the panel through a controller to a battery and run the pump off the battery via a timer.
So, you need to build redundancy into your system.
As a rule of thumb you need a battery that will run your pump for 3 days without any sunlight.
Your pump is 12v at 5Watts. Watts equals Volts x Amps. So Amps equals Watts divided by Volts.
That means your pump will draw about 0.5 Amps. Rough calculation.
You want to run your pump for 6 hours a day.
Now you can calculate the Amp Hours of battery you need to run your pump by multiplying the Amps by the time you run the pump - 0.5 Amps x 6 hours = 3 Amp hours.
Now. 3 Amp hours per day x 3 days = 9 Amp hours.
This is a very small amount of energy.
SO.
My suggestion is to buy a solar panel that produces 120 Watts (in full sunlight) connect it to a lead acid battery Rated at around 50 to 70 Amp houcrs you can buy from Supercheap Auto. Connect the solar panel to the battery via an MPPT Controller rated at 10 Amps (available on EBay) . Buy a 24 hour timer and set it to when you want your pump to run - or just let it run 24 hours a day - it cannot be a big pump, maybe only the size that would run a small water feature.
Not sure of what part of Australia you are in, but we all get a fair amount of sun.
If you want more info PM me or ring me on 0413126314.
I am in Sydney, but have a little solar powered humpy out near Mudgee, so I am learning a lot about stand alone solar.
For example, I have a composting toilet at my hut that runs a fan that draws about the same Amps as your pump. I have a 250 Watt panel charging 400 Amp hours of battery, but because of the beautiful trees around my place I only get direct sunlight onto my panel for three hours a day. But my battery’s are still fully charged every time I get up there.
From my experience, you should be good to go with what I have suggested.
Face your solar panel directly North at around a 30 degree angle for maximum Australian sun.
Hope it works for you.
Pop.

[Pop Watts]

Now I see you are in Perth.
Way more sun than I will get at Mudgee.
Pop.

[Tycer]

You could just buy a solar pump. They start around US$15 on eBay and US$25 on Amazon.

[AJMD429]

When the sun is shining 'just a little' there won't be enough current to run the pump, and most motors if given 'not enough' power will either be damaged or short out the power supply, so somehow there needs to be a threshold-sensing device or circuit to engage the circuit only if enough current will be available.

A battery acts as a huge capacitor, so as long as the overall input from the solar panel meets or exceeds the pumps consumption, you would be ok, but the pump would run continuously. Five feet of appropriately-sized (plenty big) wire should not consume significant current because resistance would be negligible. The pump ought to be ok even if only 4.8 watts got to it, but probably not 1.8 watts on a low-sun day....UNLESS it is a motor specifically set up to either shut off with low voltage/current, or designed so it just pumps slower under those circumstances. I know of no conventional pumps like that, but if any would be that way it might be ones designed for solar systems. (the reason I didn't give a serious answer at first is that I haven't messed with solar pumps).

An ordinary timer circuit could consume near-zero current, and run off the solar or a small battery, and kick the pump on only for say three mid-day hours each day. Easiest would be a stand-alone timer like used for lights or other equipment, that uses a AA battery that powers it a year or more. UNLESS you find out (from the pump manufacturer?) that the pump in fact won't be damaged by low voltage, I'd still use a battery.

It may be that what makes it a 'solar' pump is that very feature.

[marlinman93]

You can definitely run the 12v. pump right off the solar panels if you simply get a 120v. power supply that converts 120v. AC to 12v. DC. These are readily available, and not that expensive these days. Running the 120v. system will be require smaller wiring also, as the current draw on the 120v. side is 10% of what the 12v. side will draw. So the closer the 120v. is run to the 12v. pump, the further you can do it with the smaller wire.
I did some solar systems not long before I retired. They were just starting to become a big thing then, and prices were dropping with competition. Be extremely careful working with solar system panels! They will generate electricity as soon as you expose them to light, and remove the shorting jumpers. Need to make sure they stay covered and jumpered until you're ready to produce energy!

[Pete44ru]

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I yam impressed with this interesting conversation - thanks for posting, folks !

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