Need help with snubber circuit for irrigation (24VAC) controller

Forums › Gadgets, robotics, home automation, electronics (including wearables) › Need help with snubber circuit for irrigation (24VAC) controller

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#1464738 6-Jan-2016 22:23

Hmm, wouldnt have thought that a ceramic would conduct enough to keep the valve open, unless it was destroyed by the back EMF and went short circuit.

Really, just order a board with solid state relays on it and problem solved.

Richard rich.ms

SumnerBoy

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#1464741 6-Jan-2016 22:27

How will that help (sorry for my ignorance)? If the problem is the solenoid is causing all the EMF then using a SSR won't make a difference will it? I thought the issue was the solenoid EMF was coming back up the VAC supply and causing interference on the Arduino power supply. One last thing I will test (which I know you mentioned earlier) was to try powering the Arduino from a separate wall wart. As I mentioned I wanted to keep the device self-contained with a single power supply but that might not be an option...

One thing to note, I had this exact same system, but using a RPi instead of an Arduino, previously and never had any issues whatsoever.

richms

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#1464750 6-Jan-2016 22:44

SSRs are triac based so will turn off when they are at no current. Therefore no/minimal EMF generated.

RPi has a much more advanced power circuit on it than an arduino, small switching regulator down to the 3.3 and whatever else it needs means it has to have lots of filtering. Arduino has just a linear regulator on the board and some weird stuff to let it switch from USB to DC jack power seamlessly which i have no idea how it actually works even after looking at the schematics.

Richard rich.ms

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#1464753 6-Jan-2016 22:45

Thanks for the explanation Rich - do you have a recommendation of where I could get a 4xSSR board suitable for this sort of task in NZ? Or am I better off trying AliExpress?

richms

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#1464756 6-Jan-2016 22:48

I would just aliexpress it, there are heaps with fake omrons for about $8 for a 4 channel one. Not 100% sure they will be all good at 24v like the larger SSRs but worth a shot at that price.

Richard rich.ms

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#1464759 6-Jan-2016 22:51

This sort of thing?

http://www.aliexpress.com/item/4-Channel-5V-Solid-State-Relay-Module-Board-OMRON-SSR-AVR-DSP/32307087979.html?spm=2114.01020208.3.46.wLmJ7w&ws_ab_test=searchweb201556_3,searchweb201644_4_10001_10002_10005_10006_10003_10004_62,searchweb201560_6,searchweb1451318400_6149

The input/control specs look fine but the output is saying 75-264VAC - bit worried that will be a problem for my 24VAC soleniods?

richms

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#1464760 6-Jan-2016 22:54

Yeah thats the sort of thing. TBH you would want to actually look up that SSR and see what they actually say about it rather than trusting some sellers copy and paste of it. Or just buy it and try it since its so cheap.

Other option is to get your own zero crossing optoisolators and triacs and roll your own. Schematics for it are all over the net, but the things stuck into a little black box with someone elses brandname printed on it are oh so convienient.

Richard rich.ms

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#1464765 6-Jan-2016 23:09

Do you use a transformer to pug in your 24VAC controller PSU?

Do whatever you want to do man.

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#1464766 6-Jan-2016 23:10

Purchased - will have to wait for them to ship from China now but hopefully that is the end of it - thanks again for your help with this!

SumnerBoy

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#1464867 7-Jan-2016 08:54

billgates: Do you use a transformer to pug in your 24VAC controller PSU?

Sorry BillGates, not sure what you mean. There is a wall wart giving me 24VAC which is used to drive the solenoids. I then feed this into a rectifier and VDC regulator to give me 9VDC to power the Arduino.

billgates

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#1464988 7-Jan-2016 10:51

SumnerBoy:

Sorry BillGates, not sure what you mean. There is a wall wart giving me 24VAC which is used to drive the solenoids. I then feed this into a rectifier and VDC regulator to give me 9VDC to power the Arduino.

Sorry, I meant to ask if you were using an transformer that downgraded from 240V to 24VAC for the power adapter? From your reply, it sounds like your electrician or yourself specially got a 24VAC power point installed in your house to drive the solenoids.

Something like this behind your wall to downgrade from 240VAC to 24VAC? Reason why I ask which solution you are using for your 24VAC is because I will be going through the same exercise in few months time with automating irrigation using Solenoids.

http://www.jaycar.com.au/Power-Products-Electrical/Plugpacks/Desktop---AC-Output/240V-to-24VAC-150W-Indoor-Transformer/p/MP3045

Do whatever you want to do man.

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#1465002 7-Jan-2016 11:11

I have a wall-wart which plugs into a standard 240VAC socket. This outputs 24VAC which drives the solenoids, and is the wall-wart that came with my irrigation controller (the old one I used to use). So nothing behind the wall, just something I plug into the wall, like a standard 5VDC mobile phone charger.

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#1465517 8-Jan-2016 00:32

What are you using as a voltage regulator to get your 5V or 9V feed to the Arduino? Also due to the RMS to peak relationship of AC, when you rectify AC you will get a higher DC voltage. Multiply ACVolts by 1.4 to get DCVolts, Which means your 24VAC will give you about 32.5VDC after allowing for voltage drop through a bridge rectifier. (So no wonder the 16V capacitor went bang)

Or maybe just post a photo of your rectifier / regulator circuit.

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#1465518 8-Jan-2016 00:38

Also do you have a circuit diagram for that relay shield? As you could probably connect it's VCC pin to the 9V. So the 5V regulator on the Arduino board will only need to run the Arduino itself. And the relay coils will be powered directly from your external 9V regulator.

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#1465661 8-Jan-2016 09:39

Here is the relay board, pretty standard 4xrelay with diodes across the inputs and transistors allowing the Arduino to drive directly. There is no opto-coupler on this one (my mistake above I thought it had them). I have another board with the opto-couplers, is this likely to make a difference tho - the diode should be stopping any back EMF from the relay?

And here is the voltage regulator;

But I don't think there is an issue here, since I just disconnected the 9V supply from the regulator and plugged the Arduino into my (battery powered) laptop and the same thing is happening when I switch the fourth relay. So in this config the Arduino is powered from the laptop battery, and the 5V pin from the Arduino is powering the relay board. The relays are switching the 24VAC from the wall wart. So this means either something else non-power related is causing this, or there is back EMF coming back through the relays, relay board and into the Arduino via the digital pins and/or the 5V pin?

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