Author Topic: Pumping water with solar - separate line required?  (Read 1933 times)

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49north

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Pumping water with solar - separate line required?
« on: September 01, 2005, 10:52:44 PM »
At our cabin rain-collected water is pumped up to an upper tank with a small Honda gas-powered pump.  From there, gravity feeds the cabin.  If (when) I get lazy about pumping water up the hill, we can hit a dry spell with a nearly empty upper tank.  I'm thinking that a small solar-driven 12V pump on a float switch would automatically keep the upper tank topped up.


Right now we just use a single line between the upper and lower tanks, with a tee feeding the cabin.  The line goes into the bottom of the upper tank through the outlet. (I thought this would never work and that the Honda pump needed a separate line to the TOP of the upper tank.  It took my brother the engineer to tell me that the pump would fill the upper tank just fine this way.  I took his word for it, and it works, though it still seems impossible to me).  


The supply line between the tanks is a fairly large diameter (1.25"), with a lift of about 40' or 50', and a run of about 150'.  Can a small 12volt pump pressurize something that large, or do I need a separate, skinnier line? (And, hey, does it go to the top or bottom of the tank?)


PS does anyone know what kind of float switch to use with a large (900 gal) poly tank?  


Thx.

« Last Edit: September 01, 2005, 10:52:44 PM by (unknown) »

maker of toys

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Re: Pumping water with solar - separate line requi
« Reply #1 on: September 01, 2005, 09:49:20 PM »
as long as you use pump with some sort of check valve, there should be no trouble with the diameter or the position of the pipe on the tank.


I'm assuming that the purpose of the switch is to keep from over-filling the tank?


if so, a 'toilet' float attached to a microswitch and oriented so that the wieght of the float turns on the switch should do nicely.


(most good hardware or plumbing stores should stock a variety of floats.  however, a reasonable substitute can be made from a soda bottle.)


-dan

« Last Edit: September 01, 2005, 09:49:20 PM by maker of toys »

wpowokal

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Re: Pumping water
« Reply #2 on: September 01, 2005, 10:01:06 PM »
The size of your delivery pipe is irelevent, a 12 solar pump can be used but you will need to specify to the supplier the head it is to work against, ie lift.


If I was using a level switch I would use a mercury wetted switch in floating blob, this would require a cable from tank to pump, and I would run a light cable to activate a relay(avoids line losses).


However I would not take that hapentrack, I would buy a pump with pressure switch built in. Plumb its discharge into the supply line at the cabin, place a non return valve at the upper tank outlet such that water can not flow back into the bottom outlet.


 Place a tee just downstream of the non return valve, I would fit a ball valve at the top of the tank and plumb this to the tee.


What this will mean is when there is sun the pressure pump will fill the tank and also start whenever water is used. This is not a problem since it would have to be pumped up anyway.


However, you should check available sola amps verses the pump requirement verses the quantity of water required each day. You may find the Honda is still the best option.


allan down under

« Last Edit: September 01, 2005, 10:01:06 PM by wpowokal »
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ghurd

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Re:
« Reply #3 on: September 02, 2005, 06:40:55 AM »
There is a sump pump, ball on a cord, type switch switch for this use.

It is backwards from a sump pump switch, meaning it turns the pump on when the water is low.

The tether would allow fairly large adjustment for minimum and maximum water levels.


I read somewhere of problems with one brand, the contacts not being suited to DC power. So to get around that, reduce line losses and wire costs, I'd connect the float switch to a mosfet (like a IRF510 or similar), controlling a relay for the pump. That way, the amps in the switch and switch wire would be close to '0' (less than 100 nanoamps).


Grainger lists 4 models, $27 to $46, "Float Switch Nc".  Main differences seem to be wire ga and length.  30 feet of tether should be enough (wow).


Study different pumps and brands for what can pump the water tank full with the least amp-hours. Usually the fastest pumps are the least efficient.  Some pumps can't handle impurities like sand and silt.


G-

« Last Edit: September 02, 2005, 06:40:55 AM by ghurd »
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ghurd

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Re:
« Reply #4 on: September 02, 2005, 07:11:47 AM »
Never have to look far from here!


Failed float switch... Read about it here, with updates.

http://www.otherpower.com/float_switch.html


Did you see this?

http://www.otherpower.com/otherpower_waterpumping.html


The homebrew float switch seems prone to cycling that is hard on the pump and efficiency, just 2 cents.

G-

« Last Edit: September 02, 2005, 07:11:47 AM by ghurd »
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49north

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Re: Pumping water with solar - separate line requi
« Reply #5 on: September 02, 2005, 02:39:48 PM »
Yes, the switch is to avoid over-filling the tank.  Come to think of it, I guess I'll need a switch in both tanks - one at the lower tank to avoid running the pump dry if the tank gets emptied, one at the upper tank to switch off the pump when the tank is full.
« Last Edit: September 02, 2005, 02:39:48 PM by 49north »

maker of toys

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limit/float switches for DC use
« Reply #6 on: September 03, 2005, 02:11:09 AM »
most switches want some current through them to break up the oxide layer, etc. Running them below about 15 mA will actually shorten their life!  (glass-encapsulated reed switches are one exception; mercury switches (and their cousins, mercury-wetted switches) are another. ) CAVEAT:  I wouldn't want mercury anywhere near water that I might use for drinking or bathing. . .


there are switches that are rated for DC use; microswitch(r) is one such brand. They market some that will switch 125 VDC and various currents, which will serve our purposes quite well as long as they are installed in a 'weathertite' enclosure.  (they're specified for 1 million make/break cycles at rated capacity. . . that's a LOT of pumped rainwater!) Figure about $60 for one equipped with the enclosure and a lever that can be fixed to the float rod. Pricey, but you'll only ever buy them once, especially if you put a moderate-sized ceramic capacitor across the contacts. (100v, 1uF per amp or so)


Or you can get a cheap switch that will handle 1/4 amp DC or so and put a cheap ($15) relay rated for 10A 125Vdc per contact next to the pump. (the potter and brumfield 'krpa' series is one). . . makes things easy from a repair point of view, but uses about 1/2 watt more power than the straight switch while the relay is pulled in. You might make that up in shorter high-current cable runs, though.


if you're a little handier with the soldering iron and electronic theory, a virtually foolproof 'forever' switch can be made with an LED and a Photodiode or Phototransistor, which can then drive your IRF 510 or 610 MOSFET.  In fact, some surplus/ supply houses (jameco) sell 'photointerrupter' sets out of printers, etc., that are already set up for this sort of thing. Just be sure and test it before potting the electronics in polyester or epoxy resin to keep out water. . . (voice of experience)  The price is certainly right; about $10 including the fet and [cheap] epoxy.  figure about 5 mA of 24/7 current draw if you go this way. . . but the right FET can drive the pump with no intermediate relay.  (International Rectifier sells MOSFETS that will handle 10+ amps in a to220 package, and you can gang the FETS togeather for any desired current flow. again, the FETs can be right next to the pump, reducing the need for long runs of high-current cable.


ghurd's point about getting the pump that handles the most gallons per WattHour is well taken. . . .


-Dan

« Last Edit: September 03, 2005, 02:11:09 AM by maker of toys »

Kevin L

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Re: limit/float switches for DC use
« Reply #7 on: September 07, 2005, 06:08:35 AM »
I wouldn't want a mercury switch anywhere near my water supply.  I would stick with a micro switch to give you peace of mind.
« Last Edit: September 07, 2005, 06:08:35 AM by Kevin L »