What is best DC system voltage for our pump/solonoid system?

[cupoftea]

Hi,

We want to make a domestic household plant watering system for peoples' second homes which are usually empty. (also for when people go on holiday).

So , the plants are in racks, we wish to pump water from the household mains water supply into a low level sump with level detectors in it. Ie, a solenoid valve will open and allow mains water into the low level sump. Water will get pumped from the low level sump to the high level “tank”. From the high “tanks”, water will flow down to the plants by gravity through tubes. Moisture sensors will detect when more water is needed for the plants.

So, power will ultimately come from the mains. What is the best isolated DC system voltage to use? Ie, which voltage is best for powering the pump and solenoid? We want it cheap as possible, but we also want it all to last as long as possible. I mean, 12V?, 24V? 48V? At what voltage are these pumps and solenoids cheaper?

(There is a rainwater “channel thing”, which also directs rainwater into the low level sump, so hopefully we wont need to switch the mains water on too much)

 

[barry]

You do realize that they have mains powered pumps and solenoids, right? So you won't need a power supply?.

I don't believe there's significant difference in cost between devices with different voltages.

 

[cupoftea]

Thanks yes, but we need these switchable by a micro on an isolated 5V supply. We only want mains coming to the input of the offline SMPS...after that we want everything low voltage DC.

Thing is, you would think a very low power pump would be cheaper as a 12V pump, rather than as a 24V pump?

 

[barry]

Thing is, you would think a very low power pump would be cheaper as a 12V pump, rather than as a 24V pump?

I wouldn't think that. A watt is a watt.

 

[D.A.(Tony)Stewart]

This ought to be doable with a car battery with float charger for low ESR and high surge capacity.

if excessive, then a large SLA 12V maybe depending on ratio of motors DCR to battery ESR ought to be <10%

 

[Easy peasy]

24VDC is a marine standard for reliable pumps of all sizes.

 

[KlausST]

Hi,

Depending on your requirements and pump type, maybe a RPM controlled BLDC motor may help to save power.

Klaus

 

[c_mitra]

which voltage is best for powering the pump and solenoid? We want it cheap as possible, but we also want it all to last as long as possible. I mean, 12V?, 24V? 48V? At what voltage are these pumps and solenoids cheaper?

You will notice that most pumps come integrated with motors and they are the cheapest.

It depends where you are located, but 220VAC induction motor coupled with a centrifugal pump is likely to be the cheapest. a 350W motor and a single stage centrifugal pump will be able to pump water happily 15m but you need to check.

These motors are single phase capacitor start and can be put on/off using a heavy duty but otherwise regular relay with a 12V DC coil.

About watering your plants: how much water you want to deliver over how long period may determine the type of solenoid valve. Big solenoid valves can be expensive but I do not think that depends on the coil voltage. If you have potted plants, you may use individual valves for individual pots. Even with more valves, you may be able to keep the cost low.

Unless you provide more information, no meaningful suggestion can be made.

 

[cupoftea]

24VDC is a marine standard for reliable pumps of all sizes.

Thanks....i dont know why, but i just also think that overall we will have more choice if we pick 24V. In terms of cost and longevity.

a 350W motor and a single stage centrifugal pump will be able to pump water happily 15m

...sorry i should have said, this is pumping water up 2 metres at the highest, and we are looking at a pump of around 20W maximum...and of course, most of the time, it wont be pumping at all.

Depending on your requirements and pump type, maybe a RPM controlled BLDC motor may help to save power.

...thanks, that sounds interesting...kind of making up our own pump

BTW, do you think its worth supplying the pumps via shielded cable?......also, all the wiring of this kit will not be in a totally sealed enclosure....the bits will all just be screwed to a thin metal panel. I am actually wondering whether every wire, even the wires leading off to the NTC to measure water temperature, should all be in shielded cable?

 

[KlausST]

Hi,

Electromagnetic valves need full voltage only for the fisrt time, then the voltage may be PWM´d.
maybe 50% or even down to 25%. Read the datasheet or test it.

50% PWM may reduce power consumption and heating down to 25%
25% PWM may reduce power consumption and heating down to 7%

You need to decide if it´s worth the effort.

Klaus

 

[cupoftea]

Electromagnetic valves need full voltage only for the fisrt time, then the voltage may be PWM´d.
maybe 50% or even down to 25%. Read the datasheet or test it.

Thanks Klaus, sorry , i should have said, the solenoid will let through mains water, and will likely only be opened for maybe 10 seconds per day at most. But yes....after 1 second of actuation, we will PWM down as you say.

 

[D.A.(Tony)Stewart]

I would first define all the interface specs including HMI and cost. Then search for suitable solutions. It could be realized quickly, efficiently at budget costs , but only after details specs are determined and listed.

 

[Externet]

A lot of effort to reinvent the wheel. Abundant on the market :

----> https://www.ecosia.org/images?q=irrigation timer

And if water comes from mains or elevated tank, no pump needed.

 

[Kajunbee]

@Externet, I was thinking the same thing because I had one of those type at my home. I’m not a plant expert but rainwater is considered to be better for plants than city or well water because of its purity. But anyway if you can afford to have a summer home you probably won’t mind the extra cost of the system treez is proposing.

 

[Kajunbee]

--- Updated Nov 6, 2021 ---

The amount of noise these pumps create seems to be a common complaint.