Dry run protection for DC Solar Pump sourcing water from a borehole

Thread Starter

bk268

Joined Apr 19, 2017
6
We are installing solar power irrigation systems for smallholding farmers in Rural Ghana,

We have 12V DC 0.18kW (max 20A) pumps, there only power source will be a voltage varying from 15-20V coming from solar panels.

The boreholes are narrow, therefore is not much room for a float switch,

The max flow is 20 Litres per minute but more typical flows would be 5-10 liters a minute

Can anyone advise on flow or pressure switch solutions (I have done a google but I don't have experience in this area and am not confident myself)

Ideally, there would be no second power source or battery needed, and the solution should be as low-cost as possible. something under £20 per unit for 20 units would be ideal.

(It's a charity project replicating 20 units - so cost is important)

let me know if i missed out any key info
 

Sensacell

Joined Jun 19, 2012
3,504
We are installing solar power irrigation systems for smallholding farmers in Rural Ghana,

We have 12V DC 0.18kW (max 20A) pumps, there only power source will be a voltage varying from 15-20V coming from solar panels.

The boreholes are narrow, therefore is not much room for a float switch,

The max flow is 20 Litres per minute but more typical flows would be 5-10 liters a minute

Can anyone advise on flow or pressure switch solutions (I have done a google but I don't have experience in this area and am not confident myself)

Ideally, there would be no second power source or battery needed, and the solution should be as low-cost as possible. something under £20 per unit for 20 units would be ideal.

(It's a charity project replicating 20 units - so cost is important)

let me know if i missed out any key info
If the power comes directly from the solar panels, I would worry that the pump might not start correctly as the sun comes up.
It might just sit there getting hot as the voltage slowly rises - until it dies.
An under-voltage lockout would fix this. (but maybe your pump is brushless?)

A rotary vane flow sensor could detect the flow of water, with a bit of logic that starts the pump, waits a period for flow, then times-out for a longer period If the flow doesn't start in a few seconds.
If the flow fails, it waits an hour and tries again?
 

LowQCab

Joined Nov 6, 2012
4,300
~$20.oo is the buga-boo.

You need a "Vacuum-Switch", ( Connected to the Inlet of the Pump ),
and a "Delay-Off" Timer, to prevent "Short-Cycling",
a "Low-Voltage-Lock-Out" Module with built-in hysteresis, also to prevent "Short-Cycling",
and a Push-Button-Switch, ( rated IP-65 for Water ), for Manual-Priming of the Pump,
and a Mechanical-Relay, which can handle the ~20-Amps @ ~12-Volts DC,
( a "Bosch-Style", Automotive "Cube-Relay" would probably work just fine ).

And while you're at it .....
a Thermostatic-Over-Heat-Switch would be a valuable addition.
( There is, of course, a slim-chance that the Motor has one built-in to it from the factory )

The Timer-Module, LVLO-Module, Relay, and Switch, must be mounted in a Sealed-Aluminum-Box.
It would be advantageous to also mount the Vacuum-Switch inside the Box if possible,
and then run only a Rubber-Hose to the Pump-Inlet.

This will easily blow your budget.
Some Training given to a few trusted workers may be the best overall solution.
.
.
.
 

Thread Starter

bk268

Joined Apr 19, 2017
6

Thread Starter

bk268

Joined Apr 19, 2017
6
~$20.oo is the buga-boo.

You need a "Vacuum-Switch", ( Connected to the Inlet of the Pump ),
and a "Delay-Off" Timer, to prevent "Short-Cycling",
a "Low-Voltage-Lock-Out" Module with built-in hysteresis, also to prevent "Short-Cycling",
and a Push-Button-Switch, ( rated IP-65 for Water ), for Manual-Priming of the Pump,
and a Mechanical-Relay, which can handle the ~20-Amps @ ~12-Volts DC,
( a "Bosch-Style", Automotive "Cube-Relay" would probably work just fine ).

And while you're at it .....
a Thermostatic-Over-Heat-Switch would be a valuable addition.
( There is, of course, a slim-chance that the Motor has one built-in to it from the factory )

The Timer-Module, LVLO-Module, Relay, and Switch, must be mounted in a Sealed-Aluminum-Box.
It would be advantageous to also mount the Vacuum-Switch inside the Box if possible,
and then run only a Rubber-Hose to the Pump-Inlet.

This will easily blow your budget.
Some Training given to a few trusted workers may be the best overall solution.
.
.
.
thanks for your suggestions,

We are very keen to get some sort of protection, it's a self-priming pump so that's not an issue, what sort of cost do you think that would come at? could those components run dirrectly of solar or would a PWM power supply be needed?

And why a vacuum switch rather than a pressure or flow sensor?

thanks again
 

LowQCab

Joined Nov 6, 2012
4,300
No, PWM-Controls would not be advantageous.

You evidently don't need "Under-Voltage-Protection".

But, ( I'm guessing ), the Pump-Seals may fail if run dry,
and this is what You are trying to avoid.

If the Pump is sometimes run with just an open-ended-Pipe,
then little, or no, Pressure will be generated.
This would make a Pressure-Switch fail to operate.

Flow-"Sensors" generally have moving parts that wear from
pumping Sand or other debris, and are subject to clogging,
and will require an Electronic interfacing Circuit.
There are also Flow-"Switches" which would be far more practical,
but both require substantial Plumbing modifications to install.

A Vacuum, at the Pump-Inlet, will always be present when the Pump is moving Water.
A Vacuum-Switch is generally not affected by wear, or clogging situations,
but, depending on the design,
may not tolerate severe Weather, or operating under-water.
However, there are designs that are pretty-much bullet-proof, and very simple,
which means less chance of failure.

A Vacuum-Switch only requires a small hole to be drilled into the Inlet-Pipe
for a Brass rubber-hose-barb-fitting.
The only skill needed is for Tapping the Threads for the Fitting,
and in Plastic-Pipe this is very easy.
There is a possibility that there is already an
existing 1/4"-NPT "Gauge-Port" on the Inlet of the Pump.
This would allow mounting the Vacuum-Switch in a Sealed-Aluminum-Box for protection,
instead of being exposed to certain death in the Elements.

Vacuum-Switch .......... ~$5.oo each
https://www.alibaba.com/product-det...t_catalog.normal_offer.d_title.4f527844cGDMTi
Talk to some of the Chinese manufacturers about buying 100+ Switches so you'll have replacement spares,
otherwise you'll be dealing with standard Industrial/Commercial Manufactures that
will want ~$50.oo to ~$100.oo per-each-part.

The only other parts would be an Automotive-Relay, ( ~$6.oo each, available at all Auto-Parts Stores ),

a weather-proof-Push-Button, ( IP-65 rated for Water ), ( ~$7.oo each ),
https://www.digikey.com/en/products/detail/e-switch/PV2H640NN/3777995

a short piece of Rubber-Hose, ~$1.oo,

and a "sealable" Aluminum-Box .......... ( ~$27.oo )
https://www.digikey.com/en/products/detail/bud-industries/CN-6708/1219193
( a more appropriately sized Box can be selected after the other parts have been decided upon ),
no matter what scheme You decide on,
if it's not in a sealed-Box, it's gauranteed to fail in the Elements.

This project still comes out to way more than ~$20.oo, no matter how You do it.
Just a protective-Box puts You over-budget.
.
.
.
 

Picbuster

Joined Dec 2, 2013
1,049
No, PWM-Controls would not be advantageous.

You evidently don't need "Under-Voltage-Protection".

But, ( I'm guessing ), the Pump-Seals may fail if run dry,
and this is what You are trying to avoid.

If the Pump is sometimes run with just an open-ended-Pipe,
then little, or no, Pressure will be generated.
This would make a Pressure-Switch fail to operate.

Flow-"Sensors" generally have moving parts that wear from
pumping Sand or other debris, and are subject to clogging,
and will require an Electronic interfacing Circuit.
There are also Flow-"Switches" which would be far more practical,
but both require substantial Plumbing modifications to install.

A Vacuum, at the Pump-Inlet, will always be present when the Pump is moving Water.
A Vacuum-Switch is generally not affected by wear, or clogging situations,
but, depending on the design,
may not tolerate severe Weather, or operating under-water.
However, there are designs that are pretty-much bullet-proof, and very simple,
which means less chance of failure.

A Vacuum-Switch only requires a small hole to be drilled into the Inlet-Pipe
for a Brass rubber-hose-barb-fitting.
The only skill needed is for Tapping the Threads for the Fitting,
and in Plastic-Pipe this is very easy.
There is a possibility that there is already an
existing 1/4"-NPT "Gauge-Port" on the Inlet of the Pump.
This would allow mounting the Vacuum-Switch in a Sealed-Aluminum-Box for protection,
instead of being exposed to certain death in the Elements.

Vacuum-Switch .......... ~$5.oo each
https://www.alibaba.com/product-det...t_catalog.normal_offer.d_title.4f527844cGDMTi
Talk to some of the Chinese manufacturers about buying 100+ Switches so you'll have replacement spares,
otherwise you'll be dealing with standard Industrial/Commercial Manufactures that
will want ~$50.oo to ~$100.oo per-each-part.

The only other parts would be an Automotive-Relay, ( ~$6.oo each, available at all Auto-Parts Stores ),

a weather-proof-Push-Button, ( IP-65 rated for Water ), ( ~$7.oo each ),
https://www.digikey.com/en/products/detail/e-switch/PV2H640NN/3777995

a short piece of Rubber-Hose, ~$1.oo,

and a "sealable" Aluminum-Box .......... ( ~$27.oo )
https://www.digikey.com/en/products/detail/bud-industries/CN-6708/1219193
( a more appropriately sized Box can be selected after the other parts have been decided upon ),
no matter what scheme You decide on,
if it's not in a sealed-Box, it's gauranteed to fail in the Elements.

This project still comes out to way more than ~$20.oo, no matter how You do it.
Just a protective-Box puts You over-budget.
.
.
.
The maximum dept of your water source inlet should be =<9meter below surface (10 meter approx is absolute vacuum. Hence no pumping possible form surface)

All other information is already given in previous conversation.

Picbuster
 
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