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Topic: Relay and back EMF (Read 3 times) previous topic - next topic

daytrader152

Hi everyone,

I am debugging a garbage-character LCD problem which only happens when the relay is turned on and drives a 1A/12V solenoid. Initially I thought maybe my custom-designed relay board was the problem, so I ordered a simple relay from eBay:

http://www.ebay.com/itm/221162886568?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649

Then I stripped down my circuit to bare minimum consisting only of Arduino Uno, relay module from eBay, and the 1A/12V solenoid. All I do is turn on the relay every two seconds and turn it off every two seconds. What happens now is that when the relay is triggered and solenoid is active, I lose my PC's serial port connection to the Arduino. If the relay is triggered without the solenoid connected to it, the serial port connection is rock solid.

Is this normal for PC's serial port connection to drop when solenoid is active? It seems like back EMF to me. Your advice is appreciated.

Thanks,
George

dc42

#1
Dec 20, 2012, 07:58 am Last Edit: Dec 20, 2012, 08:00 am by dc42 Reason: 1
It sounds like a wiring or power supply issue to me. Post a photo of your setup and preferably a schematic too, then it will be easier for us to help.

Back emf is generated when the solenoid is switched off rather than on, and can be tamed by connecting a diode in parallel with the solenoid, cathode to positive end, anode to negative end.
Formal verification of safety-critical software, software development, and electronic design and prototyping. See http://www.eschertech.com. Please do not ask for unpaid help via PM, use the forum.

daytrader152


It sounds like a wiring or power supply issue to me. Post a photo of your setup and preferably a schematic too, then it will be easier for us to help.

Back emf is generated when the solenoid is switched off rather than on, and can be tamed by connecting a diode in parallel with the solenoid, cathode to positive end, anode to negative end.


Attached is a photo of my barebone circuit. The wires are labelled in red. Please let me know if you need more info.

One correction to my previous posting. The serial connection drops when the relay/solenoid is turned OFF, not ON as stated in my previous posting.

Many thanks!
George

dc42

Try moving the Arduino further away from the solenoid and its wiring. In particular, that coil of red wire will create a varying magnetic field when the solenoid switches on or off, which will induce currents in anything close to it.

Also connect a power diode in parallel with the solenoid (1N4001 will do), or a snubber network across the relay contacts.
Formal verification of safety-critical software, software development, and electronic design and prototyping. See http://www.eschertech.com. Please do not ask for unpaid help via PM, use the forum.

daytrader152


Try moving the Arduino further away from the solenoid and its wiring. In particular, that coil of red wire will create a varying magnetic field when the solenoid switches on or off, which will induce currents in anything close to it.

Also connect a power diode in parallel with the solenoid (1N4001 will do), or a snubber network across the relay contacts.


Many thanks. Removing the coil of red wire and placing the Arduino further away indeed did the trick. Using the relay module from eBay, the serial port connection does not drop after the solenoid is deactivated. Then I switched back to my own custom-designed relay module. The serial port connection does not drop, but the text from Arduino stops after about 30 seconds of activating/deactivating the solenoid. The main difference between the relay module from eBay and my own relay module is the addition of a photo-coupler for the eBay one. Is the photo-coupler recommended for the relay module? It seems to isolate the "noise" better. Thanks a lot.

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