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Solar water pumping question (no battery)

 
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sam_uk



Joined: 20 Oct 2008
Posts: 370

PostPosted: Wed Apr 16, 2014 1:31 pm    Post subject: Solar water pumping question (no battery) Reply with quote

Hi I need to get water up a 10meter hill to water a garden. It will pump into a 1000litre IBC holding tank.

I have a 80watt, 19v solar panel I can use.

I'm looking at this 36, 12v watt pump: http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=261448372099&fromMakeTrack=true&ssPageName=VIP:watchlink:top:en&autorefresh=true

How can I cheaply regulate the 80 watts to 36 watts? Do I need to worry about the extra 7 volts? Or will the pump cope with that?

I'd like to use the 80watt panel so it works on cloudy days, rather than putting a 40watt panel and only have it working occasionally.

I'd like to avoid using a battery if I can.

Thanks

Sam
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sam_uk



Joined: 20 Oct 2008
Posts: 370

PostPosted: Wed Apr 16, 2014 1:40 pm    Post subject: Reply with quote

Maybe this would do the volt & amp regulation?
http://www.DODGY TAX AVOIDERS.co.uk/DEOK-Converter-Regulated-Supply-Waterproof/dp/B00HLYOOJG
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adam2
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Joined: 02 Jul 2007
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Location: North Somerset

PostPosted: Wed Apr 16, 2014 2:42 pm    Post subject: Reply with quote

It would probably be best to use a battery.
If the pump is to be used only in sunlight or bright daylight then a small and cheap battery should do.

A standard 12 volt pump wont work well or reliably without a battery.
The pump will require several times the normal running current whilst starting, and may not start at all without a battery.
19 volts if prolonged might burn out the pump.
At less than about 6 volts the pump wont run at all.
In bright but cloudy conditions the PV module probably wont produce enough to turn the pump, but the addition of a small battery would help a lot.
(direct solar powered pumps do exist, for community water supply, livestock watering and the like. they are rather expensive and arguably OTT for this application)
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emordnilap



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PostPosted: Wed Apr 16, 2014 2:51 pm    Post subject: Reply with quote

We have a small set-up with a bilge pump, battery, regulator and 12v timer to pump water out of a buried IBC. It works well, if slowly. But speed and pressure are not necessary for our purposes and the system is simple enough for even me to understand. Laughing
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sam_uk



Joined: 20 Oct 2008
Posts: 370

PostPosted: Wed Apr 16, 2014 5:13 pm    Post subject: Reply with quote

Hmm that's annoying.


Sticking with the batteryless dream:
Do you reckon 50/60watts would be enough to get it started?

Perhaps I could use a photosensitive switch:
http://www.ebay.com/itm/DC-5V-18V-Solar-Light-Control-Switch-Module-Controller-Day-Work-Night-Off-B-Typ-/390817894812?pt=LH_DefaultDomain_0&hash=item5afe8fd19c

To kick in when light levels equal 50/60 watts of output from the solar?

I'm reluctant to use a timer as on a sunny day I want it to run for eight hours (plants need watering) on a cloudy day I don't want it running for eight hours as it will kill the battery.


Or failing that if I have to use a battery:

I guess I could use a charge controller with low voltage disconnect and still include the photoswitch too. The problem I find with the LVD things is they only cut in at 11volts & cycling the battery to 11v every day isn't going to do it any good..
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adam2
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Location: North Somerset

PostPosted: Wed Apr 16, 2014 7:54 pm    Post subject: Reply with quote

I would consider a charge controller and cheap battery.
Wire such that the charge controller turns the pump on and off according to the battery voltage.
This will indeed cycle the battery down to about 11 volts which is too low for a decent battery life.
Use a cheap or second hand battery and accept regular replacement.
An old car battery is one possibility, another would be a smallish sealed lead acid battery as are widely used in fire alarm systems. These can sometimes be purchased for the scrap price, and are still worth the same when you have finished with them.

A better long term solution would be a dedicated direct solar pump, but that would be a considerable investment.
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sam_uk



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PostPosted: Wed Apr 16, 2014 10:42 pm    Post subject: Reply with quote

It doesn't make sense to me to start every day with a flat battery, particularly when the cut-in voltage is often 13v. I'd spend all morning just charging the battery.

I might try one of these: http://www.ebay.co.uk/itm/12V-MINI-PROGRAMMABLE-LOW-VOLTAGE-DISCONNECT-LVD-PROTECT-YOUR-BATTERIES-/271449762737?pt=UK_Gadgets&hash=item3f33aaabb1

You can program the disconnect voltage, so I could have the batteries kept up to 12.3 or so all the time.

I'd obviously need a cheap over-voltage regulator too.
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kenneal - lagger
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PostPosted: Thu Apr 17, 2014 3:12 am    Post subject: Reply with quote

You could go down to 11.4V and still only be discharging the battery to 50%. This would give a battery life of about 5 years. We've done this with our 12V, 920Ahr set up and they are over 5 years old now and still going (he touches wood very quickly!!!)
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Catweazle



Joined: 17 Feb 2008
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Location: Little England, over the hills

PostPosted: Tue Apr 22, 2014 10:51 am    Post subject: Reply with quote

Instead of a battery you could use a capacitor to give the pump motor the kick it needs to start spinning, it would then run from the panel until the panel output was too low, when the controller would once again charge the capacitor. This might cause frequent stop/starts if not carefully set up.
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adam2
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PostPosted: Tue Apr 22, 2014 12:06 pm    Post subject: Reply with quote

Catweazle wrote:
Instead of a battery you could use a capacitor to give the pump motor the kick it needs to start spinning, it would then run from the panel until the panel output was too low, when the controller would once again charge the capacitor. This might cause frequent stop/starts if not carefully set up.


That would work but for satisfactory operation would need a very large capacitor, probably at prohibitive cost.

At times of low PV output, the module would charge the capacitor, which when "full" would run the pump.
5 minutes running might be reasonable to aim for.

A one farad capacitor will supply one amp for one second for a one volt change in voltage.
If the pump uses 3 amps, and the acceptable voltage range is 3 volts (from 11 volts to 14 volts) then a one farad capacitor will run the pump for one second.
A 300 farad capacitor would run the pump for 300 seconds or 5 minutes.

300 farad capacitors do exist but are very expensive.

I would use a cheap battery or consider a dedicated solar pump.
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sam_uk



Joined: 20 Oct 2008
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PostPosted: Tue Apr 22, 2014 4:15 pm    Post subject: Reply with quote

Well the 20 pump arrived today. As predicted the panel won't start it alone, so i'm going to go the battery route.

The good news is the pump does have enough power to deal with the 10meter head and 100m of hose.

I think i'll get one of these: http://www.reuk.co.uk/buy-REUK-SUPER-LDR-DUSK-DAWN-RELAY-CONTROLLER.htm and set it up to turn on when the light level results in a panel output is 30watts.

That way the battery will stay fully charged and the pump will just use the 'excess' solar power in operation.
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