AC/DC High Voltage Low amperage Solenoid for pump switching

Thread Starter

radicalfarm

Joined Aug 29, 2007
11
I am looking for advice as can't find what is likely a simple answer to people with knowledge...

Pump: dual power supply: 240V AC (grid) and 300V DC (solar).
On sunny days, the pump is on solar, during cloudy days / night time the pump is on 240v AC (currently manually switched)

Goal 1 (short): To turn a dual power supply pump on & off depending on the level in a tank without having high voltage go through afloat switch.
Can use a simple remade kit to turn the pump on & off depending on the level, however these kits can normally only handle 110v /240V AC, meaning a solenoid would be needed. Trouble is, finding a reasonably priced solenoid for 300VDC (only a few amps) is proving difficult.

Can a lower voltage, higher amperage solenoid be used?
Am I approaching this wrong?


Goal (full) - maybe wishful thinking!:
An integrated circuit that can:
- monitor the tank level, maybe a visual display of said level.
- turn the pump off when tank is full, start when level drops.
- switch the power to the pump when at a certain level and the light level is low
- issue a warning signal when tank hits a low level.
- switch a solenoid when tank hits a lower level.
- switch another solenoid when tank is critically low to avoid air entering the system.

Would Arduino suit this?

Any help or direction would be appreciated as no previous knowledge in these things!
 

Reloadron

Joined Jan 15, 2015
6,703
As to measuring a tank level sans using a float switch system there are several options. There are ultra sonic methods and pressure methods with both working fine. The choice of sensing method depends on a few things like cost and environment a nice clean environment when a tank has relatively clean water or solution is simple. depends on the tank.

Switching higher voltages DC is always a challenge, well not a challenge but has a price. Whenever I measured tank levels I used low voltage DC and then used that to control my higher voltage switching applications, so you want a switch using a low DC voltage control. Part of the game is knowing not just the voltage but knowing how much current you need to switch. A relay or contactor capable of 300 VDC even at only 5 Amps won't come cheap and if the pump is 300 VDC @3 Amps you need to allow some headroom.

I guess the first step is level detection. Must admit I never saw a pump which runs on 300 VDC or AC mains voltage like 120 or 240 VAC.

Ron
 

Thread Starter

radicalfarm

Joined Aug 29, 2007
11
Thanks Ron - the pump is Grundfos SQFLEX and has built in MPPT for DC so great for solar.

The pump draws maximum 8.4A so the relay / solenoid / switch would need to handle that. I am hoping someone can direct me to a product that would suit...
 

Thread Starter

radicalfarm

Joined Aug 29, 2007
11
Updated the question with more details:

I am looking for advice as can't find what is likely a simple answer to people with knowledge...

Pump: dual power supply: 240V AC (grid) and 300V DC (solar). Draws 8.4A max (soft start).
On sunny days, the pump is on solar, during cloudy days / night time the pump is on 240v AC (currently manually switched)

Goal 1 (short): To turn a dual power supply pump on & off depending on the level in a tank without having high voltage go through afloat switch.
Can use a simple remade kit to turn the pump on & off depending on the level, however these kits can normally only handle 110v /240V AC, meaning a relay or solenoid would be needed? Finding a reasonably priced solenoid or relay for 300VDC (only a few amps) is proving difficult.
The switching side would have to be 240v AC if using one of these kits I am guessing.
examples:
https://www.ebay.com.au/itm/Automat...ump-On-Off-NC-Level-Float-Switch/141651592278
https://www.ebay.com.au/itm/C61F-GP...Pump-Switches-Liquid-Level-Relay/382636578480
https://www.ebay.com.au/itm/DF-96A-...-Pump-Cistern-Auto-Liquid-Switch/282952856753

Can a lower voltage, higher amperage relay/solenoid be used?
Or am I approaching this wrong?


The eventual result is something like the below (but the above is the immediate need):
An integrated circuit that can:
- monitor the tank level, maybe a visual display of said level.
- turn the pump off when tank is full, start when level drops.
- switch the power to the pump when at a certain level and the light level is low
- issue a warning signal when tank hits a low level.
- switch a solenoid when tank hits a lower level.
- switch another solenoid when tank is critically low to avoid air entering the system.

Would Arduino suit this?

Any help or direction would be appreciated as no previous knowledge in these things!
 

dendad

Joined Feb 20, 2016
4,168
To detect the levels, an Arduino generating a 50% PWM signal, capacitive connected to a stainless steel probe can be used. Then, have other probes at different levels that have a rectifier feeding analog inputs are used to show the presence of water at each probe.
Or, using an ultrasonic sensor.
Or, a pressure sensor.
Or.... quite a few others.

When you purchase a relay/contcator for the motor, make sure is has a DC rating on the contacts. DC requires better contacts than AC as the arc when stitching is not self quenching.

Have a go at drawing out a circuit or block diagram first. How do you intend safely selecting the mains or the solar to drive the pump?
 

MisterBill2

Joined Jan 23, 2018
12,402
First there is additional information needed before any help can be provided. Is the 240 volt mains power available at all times? Is it possible to have a mains powered low voltage supply to operate a control relay? And is it possible to have float switches, or some type of level sensing switches, operate at each of the levels that are mentioned? And what part of the world is the system located in? That usually affects the availability of the resources available to create a solution.
 

Thread Starter

radicalfarm

Joined Aug 29, 2007
11
Thank you - noted

How do you intend safely selecting the mains or the solar to drive the pump?
I am not sure yet I was hoping there was a 'simple' 3 way isolator rated to 300VDC that could be used.
I = 240VAC grid, 0 = off, II = 300Vdc Solar
 

Thread Starter

radicalfarm

Joined Aug 29, 2007
11
First there is additional information needed before any help can be provided. Is the 240 volt mains power available at all times? Is it possible to have a mains powered low voltage supply to operate a control relay? And is it possible to have float switches, or some type of level sensing switches, operate at each of the levels that are mentioned? And what part of the world is the system located in? That usually affects the availability of the resources available to create a solution.
I am in Australia. The 240v power can be available at all times and yes that could drive a power supply.
Yes float switches were planned to be used at each of the levels.

Thank you!
 

dendad

Joined Feb 20, 2016
4,168
Depending on what you want to spend, a hybrid inverter system may be a good way to go.
3KW_Inverter.png
Then run the pump on AC all the time, and get battery backup as a bonus.
Using AC makes the selection of the switching relay a lot easier. Have the relay driven from an Arduino that looks at the levels of a couple of float switches and has an interlock to stop the pump if the water supply is to low so you do not run the pump dry.
A pressure sensor could be used in place of the float switches, or as well as them, to show the current tank level.
 

Reloadron

Joined Jan 15, 2015
6,703
To turn a dual power supply pump on & off depending on the level in a tank without having high voltage go through afloat switch.
You can use low voltage in a float switch? Would that be OK?

Nobody here can see this tank, is it open top or closed? How large as in dimensions and capacity?

Yes float switches were planned to be used at each of the levels.
How many levels? What do you want to happen at each level? You need to start getting specific if you want good help and suggestions.

Yes, you can use a uC and just about any uC including an Arduino. Using an ultrasonic sensor you can even have a readout displaying tank level, pump power source and whatever you want. Most of this goes to the environment everything is in. Personally I would likely run with an inverter so the pump is always run on AC and that will cut cost of a high voltage / current DC contactor.

Ron
 

MisterBill2

Joined Jan 23, 2018
12,402
I have done a similat control system for both air pressure tanks and for hydraulic fluid tanks and the good news id that the control function does not require anything smarter than relays. I usually used Allen Bradley 700N series relays because they last a long time and they are quite rugged. But relays that cost a whole lot less can work very well also. The big challenge is having a motor powered by either 240 volts AC or 300 volts DC. If a BLDC motor that would work with the pump and not cost more than two motors and pumps can be obtained then one sort of simple choice would be to run it on rectified AC or on the 300 volts from the solar source. When the "RUN" command is supplied the DC source would be selected, and if the pump started to deliver flow, it would run until the "RUN" command was removed. But if the flow did not appear then the change-over to AC would be made and the pump would continue running on the rectified AC. But it may be simpler to just monitor the solar system to see if it is able to supply power to the pump. Totally no need for a little computer, ans since all of those logic level outputs would need an interface to switch big power, there would be a much simpler system.
 
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