Pump voltage

[Sheptonphil]

Well, the pump is working good from the VFD. All runs as it should.

For a control, I would like to add an auto pump shutoff when the water stops flowing (the irrigation system has an auto shut off mechanism when fully retracted).
I can use a make break type switch on a flow switch to input into the xsy at1 VFD to turn the pump off when water stops flowing, however a 1” or 1.5 inch flow switch that handles 140 litres a minute is horrendous money. However, I can get a 1.5” flow sensor for a decent price.

if the flow sensor transducer is fed 12v through the red and black, what is returned through yellow? Is it 12v return when flowing and no return when flow stops? If so can I use the 12v/ 0v input to xsy at1 VFD to control on/off the same as the make break? Is a 12v relay operated from transducer output an option?

hope it makes sense.

 

[Sandyn]

Do you have a part number for the flow sensor. It could be an analogue output which is proportional to the flow, rather than a flow switch with a 12v/0V output. You need to know the parameters of the sensor output and of the VFD input. I would put an isolating relay between the two for safety, without the correct data, it's a bit guesswork

 

[Sheptonphil]

Do you have a part number for the flow sensor. It could be an analogue output which is proportional to the flow, rather than a flow switch with a 12v/0V output. You need to know the parameters of the sensor output and of the VFD input. I would put an isolating relay between the two for safety, without the correct data, it's a bit guesswork

This is the part, flow sensor

Relevant info (I think)

Flow range:10-150L/min
Sensor:Hall effect
Maximum current:15 mA(DC 5V)
Working voltage rangeC 5¡-18 V
Load capacity:≤10 mA(DC 5V)
Operating Temp:≤80℃,Operating humidity:35%-90%RH
Allow compression:Water pressure 1.75 Mpa below
Insulation resistance:>100M OHM
Storage Temperature:-25-80℃
Storage humidity:25%-95%RH
Output Waveform:Square Wave,output pulse signal.
Cable length:480mm
Max Size: 92mm*68mm

I think if this outputs a voltage, I could use a relay to create a make/break circuit.
When water flows, voltage is used to make a circuit via relay, when water stops, voltage stops, relay breaks circuit.
If this is the case, I can use the make/break to control the VFD as I can do that with a no volt on/foo switch to short the two control contacts on the VFD.

 

[Sandyn]

OK the unit is a flow sensor, so the output is a square wave pulse train of variable frequency ( according to one review), which is proportional to the flow rate, so, you will need a small buffer circuit to convert the pulses to a voltage level which would drive a relay. A very basic circuit would be something like this.

Couldn't find a *** packet so had to use an envelope. The pulses are fed into a diode which charges the capacitor. As the Cap charges, the transistor turns on, operating the relay. As long as there are pulses present (water flow), the transistor and relay stay on. When the pulses stop, the cap discharges and the transistor and relay turns off.
An alternative is to get a voltage comparator from Amazon for a couple of quid and add the integrator circuit (Diode, resistor and capacitor) to the front end of the module. The circuit would need to be tuned for your flow rates.

 

[Sheptonphil]

OK the unit is a flow sensor, so the output is a square wave pulse train of variable frequency ( according to one review), which is proportional to the flow rate, so, you will need a small buffer circuit to convert the pulses to a voltage level which would drive a relay. A very basic circuit would be something like this.

View attachment 119097

Couldn't find a *** packet so had to use an envelope. The pulses are fed into a diode which charges the capacitor. As the Cap charges, the transistor turns on, operating the relay. As long as there are pulses present (water flow), the transistor and relay stay on. When the pulses stop, the cap discharges and the transistor and relay turns off.
An alternative is to get a voltage comparator from Amazon for a couple of quid and add the integrator circuit (Diode, resistor and capacitor) to the front end of the module. The circuit would need to be tuned for your flow rates.

Thanks Sandyn, I’ll have to pass on that, although the diagram is simple, once into diodes and capacitors, I’m lost. I was kinda hoping in ignorance it would just output a voltage. I think I’ve got to go down pressure switch route or flow switch.
thanks for your input though, it’s good to know it was a possibility (subject to ability).
phil

 

[Sandyn]

A pressure switch would be the easiest for you, one which gives a switch contact output. . I have a dis-assembled shower pump and it just uses a sliding magnet and a reed switch. The reed switch closes when the magnet slides near. It requires no power. You then use the contact closure to switch a relay with contacts capable of switching a power load/ for isolation. There will be flow switches with other designs. It's important to isolate the VFD from the pressure switch. You don't want the possibility of mains voltages getting back to the switch if there is a failure somewhere.

 

[Sheptonphil]

A pressure switch would be the easiest for you, one which gives a switch contact output. . I have a dis-assembled shower pump and it just uses a sliding magnet and a reed switch. The reed switch closes when the magnet slides near. It requires no power. You then use the contact closure to switch a relay with contacts capable of switching a power load/ for isolation. There will be flow switches with other designs. It's important to isolate the VFD from the pressure switch. You don't want the possibility of mains voltages getting back to the switch if there is a failure somewhere.

Thanks, I’ve sorted a pressure switch that will control a 240v AC coil relay. Off the relay I can take a no volt make break to the VFD terminals that I can use at present with no volt switch. A little more convoluted than the direct switching that you could do, but will work perfectly well for its intended purpose. It will only be used once, maybe twenty times a year.

 

[Sandyn]

That's a good solution. Much easier than using the flow sensor.