Valves Won't Turn Off

[vik]

Hi,

I have set up an OSPi which drives 3 separate solenoid valves.

Everything looks good from the OSPi’s perspective and I can start each valve.

The problem is, once started they won’t turn off again. I have tried both waiting for the set time to end and also using the “stop all stations” feature.

The valves do shut off if I shutdown the OSPi.

It seems like the board might be faulty, but has anyone else faced this or have an ideas of how I can troubleshoot further?

TIA

Vik

[Mike]

Hi Vik,

A couple of basic questions come to mind: What kind of valves are you using? Does the voltage to the valves turn off when you stop the stations? How are the valves wired up?
A picture of your setup might help.

Mike

[vik]

Hi Mike,

Thanks for coming back to me on this.

The valves are these ones:
http://www.access-irrigation.co.uk/shop/mist-propagation/propagation-controllers/solenoid-valve-24v-ac

I have attached an image showing one of the valves wired up. The live (brown) wire goes to the 24v terminal on the valve and back to one of the switch ports on the OSPi

The blue wire goes to the COM port on the OSPi.

I’ll test the voltage later on today and update here (although when you switch off the OSPi, the valve also shuts off – so I imagine I will find that voltage is still being supplied)

Vik

Attachments:

1. 

   IMG_0988.jpg
   

[vik]

OK, I checked the voltage.

At first the voltage shows 0.

When I start a station (for 1 minute) the voltage goes to 22.

If I stop all stations the voltage stays at 22.

The voltage stays at 22 until I restart the unit.

Any idea what could be causing that to happen?

[Mike]

Hi Vik,

I’m not sure why that would be happening but I do have one other suggestion to definitively narrow the problem down to the OSPi. Perhaps you’ve done this already, but do those voltage measurements stay the same with all of your valve wiring disconnected from the OSPi? If they do, it would completely eliminate the valves and wiring as the source of the problem. At that point you’ll have pretty much reached the extent of my ability to help but perhaps someone else will be able to chime in.

Mike

[vik]

Yeah – good call – will go and test that.

If I see the same voltage results then that would point to either the board or the software.

[vik]

OK, I tested the voltage a few further ways:

1. Voltage directly at the board

Switches On, Switches Off, behaves as expected

2. Voltage at the end of the cable

Switches On,m Switches Off, behaves as expected

3. Voltage at end of the cable with valve connected

Switches On, won’t switch off, keeps supplying voltage at 23v until I shutdown the board.

[Ray]

Are you sure you are using 24V AC transformer? The typical cause for valves not able to shut off is that the power adapter is a DC adapter. If you are not sure, you can look at the transformer’s label to see if the output voltage is AC or DC.

[vik]

Thanks for getting back to me.

I bought a 24v Switched Mode AC DC Power Supply like this:

https://www.ebay.co.uk/itm/18W-750mA-Fixed-Voltage-24V-Switched-Mode-AC-DC-Power-Supply/282416149933

And then cut the plug off the end and wired it to the board.

Looks like this is the culprit – should a switching power supply work – or should I get another one which is only AC?

[vik]

If I need to get another one, will this work?
https://uk.rs-online.com/web/p/desktop-power-supply/9076249/

[Mike]

Vik – I’m not an expert, but I believe that switched mode power supplies output DC. You should be able to test your power supply with your meter to determine if it is outputting AC or DC.

The new power supply looks like it should work. It has 24V AC output at 750mA. The one Ray sells here is 24V AC at 500mA so your is capable of supporting a higher current load.

Mike

[vik]

Mike / Ray

Thanks for the assistance – yes it appears switched mode power supplies output DC and that was the problem.

I just connected up the power supply from RS and everything is working fine!

Vik

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