Picking the right relay for my application

[dseaver]

I am trying to create a way to control a set of zone valves for an irrigation system using USB and the Arduino Diecimila. Irrigation valve use 24VAC to turn on. Will this relay work for my application?

http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail?name=PB874-ND

I know nothing about choosing relays, but I need want to turn the relay on using this type of interface

http://www.arduino.cc/en/Tutorial/ShiftOut

Because I plan to control 8 zones. will this relay along with this setup allow me to open and close the zone valves?

 

[ScottyUK]

If you can drive an LED then you can drive a solid state relay. The SSR output can control pretty much whatever you want. Have a look for products by (e.g.) Crydom, Omron, Grayhill, etc.


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If we learn from our mistakes I'm getting a great education!

 

[dseaver]

So that relay will work with my setup? and drive the valve? Awesome

 

[geekEE]

Hey Scotty, the relay that dseaver referenced does not appear to be an SSR.

Glenn

 

[Skogsgurra]

No. That is not what Scotty said. The relay needs 80 - 90 mA at 5 V and that is way beyond what the HC circuits can deliver. With a buffer between the -595, it will work.

If the 28 V 5 A DC contact spec is OK for your valves, I can't say without knowing anything about your valves.

I know for sure, though that your shift register will have a big problem with transients if you do not put a snubber or a diode across the valve.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[ScottyUK]

Thanks skogsgurra, at least one of you bothered to read what I wrote.

dseaver: no, the Digikey part you listed is not a suitable relay. Have a look in the links below for something easy to interface to your circuit.

GeekEE: you're right, it's not an SSR. I didn't say it was one. It seems pretty obvious that it's a conventional mechanical relay.

The circuit in the OP's second link has a driver circuit driving 8 LEDs. If the circuit can drive an LED then it can drive a solid state relay because almost all SSR's use an LED input to an opto-coupler. It really is as simple as substituting the SSR input in place of the LED and current limiting resistor. If deseaver chooses an SSR from one of the many manufacturers of SSRs such as...

Crydom

http://www.crydom.com/products/productFamilyList.aspx?idProductLine=2

or

Grayhill

http://lgrws01.grayhill.com/web/images/ProductImages/IO_Mod_AC_Output.pdf

...then they won't have to worry about using something like a ULN200x series driver to drive the relay from logic. The 'x' is a wildcard before anyone tells me that they can't find a ULN200x at Digikey.

If it is a specific product you're after, Grayhill's 70-OAC5-L looks a good bet assuming this isn't a big valve. There are so many options from Crydom that I am not even trying to list them. Look for one that has a DC input range which goes down to 3V or so and has an AC output. When you think you have found a suitable one I'm sure one of us will check for you.



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If we learn from our mistakes I'm getting a great education!

 

[LionelHutz]

A simple transistor between the 74HC595 and the relay coil will fix the problem. This can also make it possible to use 24VDC relay coils with higher power contacts. Much cheaper than using a solid-state relay.

You should be able to use something like a 2N3904 or 2N2222 transistor. Put the base to the output of the logic with a 2k ohm resistor between the 2 components. Put the emmitter to ground. Connect the coil between power (+5V) and the collector.

I think the ULN2003 would be the 5V logic version, would it not?

 

[LionelHutz]

Might as well give you this too,

http://www.kpsec.freeuk.com/trancirc.htm