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Relay Circuit Bouncing


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jrfarrar 
Member - Posts: 4
Member spacespace
Joined: March 17, 2003
Location: United States
Posted: August 11, 2020 at 8:55 AM / IP Logged Link to Post Post Reply Quote jrfarrar
Relay Circuit Bouncing - Last Post -- posted image.
Here is what I'm trying to accomplish. This is on a boat that has a 12v fridge. It is normally always connected directly to the house battery. What I'd like to do is run it from an AC/DC power supply while the boat is plugged in at the dock and remove the load from the battery. So the schematic shows this attempt. Basically when the AC power comes on and powers the power supply the relay should latch over and run the fridge from the AC/DC power supply. When AC power is removed the relay will switch back to the battery.
All of this works...kind of. When I apply power via the power supply the relay latches and all is well. When I remove the AC power the relay does indeed de-engerize and switch back to the battery.
HOWEVER, if shortly after removing AC power I plug it back in again..the relay starts turning on and off every few seconds. If I leave the AC power off for about 30 seconds and then plug it back in....all is well. I can not figure out what's going on to cause this "bounce".
I tried putting a diode across the coil thinking that the spike might be causing this but it did not help. My concern is that if the AC power drops quickly (it's a marina..it's not always stable) then that could send this relay clicking back and forth which I doubt is going to be good for the compressor in the fridge.
Any ideas?
Thanks!
eguru 
Copper - Posts: 340
Copper spacespace
Joined: February 04, 2018
Location: Quebec, Canada
Posted: August 11, 2020 at 10:04 AM / IP Logged Link to Post Post Reply Quote eguru
If you unplug the fridge is the relay action stable?
What is the current rating of the adapter and the fridge?
jrfarrar 
Member - Posts: 4
Member spacespace
Joined: March 17, 2003
Location: United States
Posted: August 11, 2020 at 10:21 AM / IP Logged Link to Post Post Reply Quote jrfarrar
Have not tried unplugging the fridge and trying! I will try that later when I'm down at the boat.
3A for the fridge, 10A for the adapter (I had a 5A at first and thought that might be it.... should have added that info)
jrfarrar 
Member - Posts: 4
Member spacespace
Joined: March 17, 2003
Location: United States
Posted: August 12, 2020 at 3:06 PM / IP Logged Link to Post Post Reply Quote jrfarrar
Got a chance to go down to the boat and test...yes! With the fridge unplugged the relay action is stable.
Thoughts?
eguru 
Copper - Posts: 340
Copper spacespace
Joined: February 04, 2018
Location: Quebec, Canada
Posted: August 12, 2020 at 9:46 PM / IP Logged Link to Post Post Reply Quote eguru
Is this a thermoelectric fridge or one with a motor-compressor?
Stick a diode in series with the relay coil.
jrfarrar 
Member - Posts: 4
Member spacespace
Joined: March 17, 2003
Location: United States
Posted: August 13, 2020 at 8:43 AM / IP Logged Link to Post Post Reply Quote jrfarrar
motor-compressor
Ok I had one in parallel. I'll try in series.

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