Can I use a common ground

[nzdavo]

Hello All

We have been having issues with neighbourhood cats so I decided to cobble a cat sprinkler together. I have purchased a solenoid valve, infrared sensor and a relay.

Please see my diagram attached.

The Infrared sensor requires 12V but the output is only 3V. The solenoid valve requires 12V so I thought a relay would be needed. However I can't seem to get the circuit to work off a single 12v power supply. I have 12v running to the sensor and the relay. These both share the same ground and that seems to work ok. Then I have 3V coming out of the sensor and into the coil on the relay. I want to send the negative (Highlighted in purple) to the same ground as the rest but this isn't working. If I use a separate 3v supply the whole thing works. Can anyone tell me what I am doing wrong?

I hope I have explained that properly!

Thank you for your help.

Kind Regards
David

 

[audioguru2]

You did not provide the coil voltage and its current of the relay and did not provide the output current of the sensor when its voltage is only 3V.

The coil produces a voltage spike of hundreds of volts when the relay turns off. Usually a reverse-biased diode is connected parallel to the coil to prevent the spike.

 

[nzdavo]

Hello Audioguru

Thank you for your reply.
I launched into this with little more than my high school electronics memories so please excuse my noobness!

The coil voltage is 3v. The relay is a songle srd-03vdc-sl-c  (Datasheet here - http://www.ic-on-line.cn/view_download.php?id=1824874&file=0413\srd-03vdc-sl-c_4766638.pdf)
I will measure the current of the sensor output tonight.

The sensor requires 12V in and the solenoid also requires 12V but the output from the sensor is 3V so I thought the relay would be a good work around. (Was I right?)
I wired it up (with alligator clips) and used my multimeter to check the voltages. I get 3V from the sensor only when it's not grounded. (Multimeter probes on the 3V output and 12V ground)
I also tried two AA batteries in series (giving 3V) and attached that to the coil. It worked like a charm. (The relay switched and allowed 12V to pass through to the solenoid.)
So I think it appears that I have a grounding issue with the 3V output.... and it also appears that I am in way over my head!

Cheers
David

 

[audioguru2]

Its datasheet says the relay is a Chinese "Songle" relay. What is that?? They cannot spell "single"?
Its coil current is 120mA at 3V.

I betcha the sensor cannot provide an output current as high as 120mA at 3V. Then the relay needs a transistor to drive it and the sensor drives the transistor.

Instead of a transistor and a high current relay why don't you use a low input current darlington transistor to drive the sprinkler?

 

[elboa8]

Hi Did you resolve this?