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### Topic: Controlling the ouput voltage of a Solid State Relay (Read 496 times)previous topic - next topic

#### Soderby

##### Nov 15, 2016, 04:33 pm
Hi there,

I'm a newbie who wants to open/close a solenoid valve, through an SSR (this one: http://www.electrokit.com/en/solidstate-relay-332v-40a.52596). But how do I control the exact amount of output voltage from the relay (it can vary between 24-380VAC)? I assume with a resistor between the relay and the valve, where a 600 Ohm resistor gives 24V (40 mA from the arduino).

Of course I also bought the wrong SSR, since the solenoid valve works on max 12 V and also on DC. Does it work anyway? In my naive mind I assume I can just use a 1200 Ohm resistor instead and the problem is solved - but the reality has proved me wrong before...

Here is the solenoid valve btw: http://www.electrokit.com/en/plastic-water-solenoid-valve-1-2-12v.51108

#### gpsmikey

#1
##### Nov 15, 2016, 04:53 pm
A relay does not "output a voltage" it is simply a switch.  It needs to be in series with your supply voltage for whatever you are controlling just like any other relay (which is simply a set of contacts that open and close).  The big difference with SSRs is just what voltage and AC or DC that they can handle based on the switching device inside the box.  For all practical purposes though a SSR is simply a controlled switch and does not source any voltage, just switches it.
mikey
-- you can't have too many gadgets or too much disk space !
old engineering saying: 1+1 = 3 for sufficiently large values of 1 or small values of 3

#### Soderby

#2
##### Nov 15, 2016, 05:16 pm
Ok, I hugely misunderstood how an SSR works - thanks for the explaination! And I assume my SSR is useless? Since it can't be switched to less than 24VAC and I have a 12 V power supply (and a valve that can't manage more than 12 V). I realize that this might be another dumb question, my arduino journey just started...

#### KeithRB

#3
##### Nov 15, 2016, 06:01 pm
What is powering the valve now? You might be able to use that supply and just switch it with the SSR.

#### DVDdoug

#4
##### Nov 15, 2016, 06:20 pm
Quote
Of course I also bought the wrong SSR, since the solenoid valve works on max 12 V and also on DC. Does it work anyway?
No.  Most solid AC state relays use a TRIAC.   A TRIAC won't turn-off until current falls to zero.   That's not a problem with AC, since 60-cycle AC crosses-through zero 120 times per second.   But, with DC it will not turn off until power is removed.     And, since it's got a 24-380V rating, it might not turn-on with 12V.

A DC solid state relay would work.  Of course, you need a 12VDC power supply.

A regular electro-mechanical relay will work with 12VDC  because it's just a pair contacts pulled together with an electromagnet.   (But, you usually need a driver circuit to drive the relay coil.)

Quote
In my naive mind I assume I can just use a 1200 Ohm resistor instead and the problem is solved - but the reality has proved me wrong before...
It's dangerous to reduce power-line voltage with a voltage divider (resistors).  The low voltage should be electrically isolated from the power line.   Plus, it's AC and your relay is supposed to be run from DC.

#### rogertee

#5
##### Nov 17, 2016, 03:32 am
forget the ssr it is made for switching ac voltages not good for dc what you need is a single relay shield for arduino which has built in protection for the arduino and contacts rated for 12vdc to drive the solenoid that needs its own power

#### outsider

#6
##### Nov 17, 2016, 05:47 amLast Edit: Nov 17, 2016, 05:49 am by outsider
How about a plain old transistor switch?:

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