# 12V AC relay ( cat fountain )

Discussion in 'General Electronics Chat' started by bkr1969, Dec 12, 2010.

1. ### bkr1969 Thread Starter New Member

Dec 11, 2010
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I am trying to add a PIR detector to a drinking fountain for my cat. I found a great little module here: http://www.glolab.com/dp-003A/dp-003A.html

The fountain comes with a 12V adapter that I assumed was DC out, but the specs on the pump say it runs on 12V AC, so now (I'm not somewhere that I can verify on the plug) I'm thinking it is merely a step-down so it will output 12V AC. Th PIR module will run off this and has a dedicated realy output port to switch on a relay, but after hours of searching, I'm starting to pull my hair out figuring out what type of relay to use. I plan to simply split the 12V in and run it to the PIR module and the NO terminal of a relay. What am I missing?

Last edited by a moderator: Jan 29, 2011
2. ### Bernard AAC Fanatic!

Aug 7, 2008
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The PIR runs on DC, 4 to 12V. Rectify 12 V AC & filter. Use ungegulated DC for relay & use a zenor of 5 to 6 V for PIR. Use a 12 V DC relay to control 12 V ac for pump.

3. ### bkr1969 Thread Starter New Member

Dec 11, 2010
16
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OK...that makes sense, but the circuit is now getting more and more complex in addition to growing in size. I think I might just run the PIR off of a 9V battery and use the 9V to trigger the relay. Now, however, I'm still confused about the relay needed. I assume SSR is best, but Digikey filters them by Output Type (AC, DC) This is my biggest sticking point. What is a relay outputing? I want it triggered with the signal from the PIR. The 12V AC is at 200mA. The 9V can be whatever I buy to run it. What do I need for a relay?

4. ### thatoneguy AAC Fanatic!

Feb 19, 2009
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The relay coil/signal is the 9VDC from your PIR. The Contacts/Output need to be capable of 20VAC (little extra for comfort), and 500mA for the fountain (doubled for comfort). A standard relay or SSR would work, though an SSR is a bit more expensive, lifetime is longer. Depends on how often it cycles.

5. ### bkr1969 Thread Starter New Member

Dec 11, 2010
16
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Thanks. That helped immensely. So entering the app. values at Digikey, I found the AQH1223. Please check the datasheet to assure that I'm reading it correctly

Voltage input - 1.18VDC
On state RMS current - .6A (at 600V?)

So do I just need to add the appropriate resistor to the input or will the 9V drive it? If I'm understanding everything correctly, .6A @ 600V = 0.012A @ 12V so I would need a 150 ohm resistor. Or am I looking at the LED forward current at 50mA leading to a 36 ohm resistor? Thanks again for the help.

6. ### thatoneguy AAC Fanatic!

Feb 19, 2009
6,357
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You won't need a resistor on the output.

From the Datasheet: With the input of 9V, it is driving an LED with a max voltage of 1.3 Vf @20mA

So 9V - 1.3V = 7.7V

To limit the current to 20mA: $\frac{7.7V}{20mA}=385\Omega$

385Ω is not a standard value, the closest in E24 series is 390Ω, so that would be the resistor to put between the 9V and input (LED) of the Solid State Relay.

The AQH3213 Has a 1.2A capacity and 600V breakdown, so it will suffice for your 12VAC @ 600mA. I chose the 1.2A for double the current overhead as some motors will draw double their rated current at startup.

There won't be a resistor on the AC/Ouptut of the SSR to limit current, though adding a 1A slo blow fuse may be helpful to protect the SSR if the pump stalls or fails shorted.

7. ### bkr1969 Thread Starter New Member

Dec 11, 2010
16
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Thank you very much. I knew the resistor would be at the input, not the output, but I wasn't sure which to calculate from. I'll let you know how it turns out.

Dec 11, 2010
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9. ### bkr1969 Thread Starter New Member

Dec 11, 2010
16
0

Apr 5, 2008
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Hello,

The module has a special output for a led ( the logic output) :

When you connect the SSR instead of the led it should work.

Bertus

11. ### bkr1969 Thread Starter New Member

Dec 11, 2010
16
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Why not the relay out? All the math was based on that. Mostly I'm wondering about how the AC is connected to the SSR and pump.

Apr 5, 2008
16,447
2,713
Hello,

The relays output needs a supply voltage to work:

You could tie the led on the output taking the +9 volts as supply.

What are the specifications of the pump?
You have drawn a picture that uses AC.

Bertus

13. ### thatoneguy AAC Fanatic!

Feb 19, 2009
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From the OP, the pump is 12VAC.

I haven't looked at the datasheets for the devices again yet.

14. ### bkr1969 Thread Starter New Member

Dec 11, 2010
16
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Bertus, the pump is 12V AC. It comes with a 12V AC power cord which I plan to cut the connector off of and wire as per my schematic. Is it more appropriate to use the logic out rather than the relay out for a SSR?

15. ### bkr1969 Thread Starter New Member

Dec 11, 2010
16
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Still looking for a schematic review. The AQH3213 is no longer available so I'm going with a 2213 instead. Only rated 900mA instead of 1.2A, but that is still a lot of overhead. In looking over things again, I think my schematic is wrong at the relay input. Shouldn't pin 3 be connected to +9V instead of ground? Please help me with this.

16. ### thatoneguy AAC Fanatic!

Feb 19, 2009
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Pin 3 of which part? The relay? If it is an SSR, and Relay Out is an active high signal, the second "coil/active" pin for the SSR should go to ground.

17. ### bkr1969 Thread Starter New Member

Dec 11, 2010
16
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Pin 3 of the SSR. In my previously posted schematic it goes to ground, with pin 2 getting the input from the PIR. The PIR schematic makes it look like pin 3 should go to +V.

18. ### bkr1969 Thread Starter New Member

Dec 11, 2010
16
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OK...I don't want to seem ungrateful, but I really want to make this work and am having no luck at all. Can anyone please look at the datasheet for the SSR

http://pewa.panasonic.com/assets/pcsd/catalog/aq-h-catalog.pdf

and the info for the PIR

http://www.glolab.com/dp-003A/DP003A.pdf

and tell me exactly how to wire this?

I can get the 3.5V out of the logic/LED output pin on the PIR (running on a fresh 9V battery), but nothing from the "dedicated relay out." Can I switch my AC pump with relay or not?

19. ### eblc1388 AAC Fanatic!

Nov 28, 2008
1,543
102
Don't use a 9V battery. It will be drain in a short while.

Instead get the power from the 12V AC via a voltage regulator. I have drawn you a full schmetic.

Ask here for anything you do not understand before proceed to buy the parts.

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20. ### bkr1969 Thread Starter New Member

Dec 11, 2010
16
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Thank you very much. I decided last night to run off of AC through a 7805 regulator to save the hassle of changing batteries. I can't figure out how the PIR's relay out is supposed to be used, so I played around with it and decided to use the logic out as well. I ended up with a similar schematic as you posted, though I'm using 2 wallwarts; the AC out that came with the pump, and, to power the PIR, a 12V DC out. That eliminates having to add a rectifier. It works great. Thanks again.