Controller gets hang on Relay switching

Thread Starter

ep.hobbyiest

Joined Aug 26, 2014
201
I am using a relay to turn ON/OFF the AC load. But when i turn ON and turn OFF the AC load (230 VAC) 3-4 times my controller gets hang. Here is my circuit diagram for the relay.
The ground is common in all over schematic.


relay.png

What changes do I need to do for improving the noise?
 

drc_567

Joined Dec 29, 2008
1,156
The 1N4148 diode datasheet specifies that the maximum forward bias current is only 200 ma.
It could be that by exceeding this current level in the return current loop there is a hang-up defect of some type that is occurring. So try replacing D6 with a more suitable diode such as a 1N4001 to see if there is better performance. ... Also check to see if D6 is becoming warm or hot prior to replacing.
 
I am using a relay to turn ON/OFF the AC load. But when i turn ON and turn OFF the AC load (230 VAC) 3-4 times my controller gets hang. Here is my circuit diagram for the relay.
The ground is common in all over schematic.


View attachment 247930

What changes do I need to do for improving the noise?

You need a suppressor (capacitor) to avoid the power peaks. It's better to put it on you power switch, to ground it faster. Also check your power supply rectifier as well (if you use any bridge). Sometimes the power supply doesn't act as they mention on the catalog.
 

Thread Starter

ep.hobbyiest

Joined Aug 26, 2014
201
What is the current of your load and its inrush relative to your relay, is the relay contacts sticking?
Current of the load is approx. = 8.5Amps
How close is the relay to the controller circuit?
Relay circuit and controller circuit is on the same board.
The 1N4148 diode datasheet specifies that the maximum forward bias current is only 200 ma.
It could be that by exceeding this current level in the return current loop there is a hang-up defect of some type that is occurring. So try replacing D6 with a more suitable diode such as a 1N4001 to see if there is better performance. ... Also check to see if D6 is becoming warm or hot prior to replacing.
Sure. i will try changing the diode.

You can search lot of info from Google by "suppress noise from AC load relay contact", I got this:
https://docs.rs-online.com/1091/A700000006618299.pdf
i will go through that pdf.

You need a suppressor (capacitor) to avoid the power peaks. It's better to put it on you power switch, to ground it faster. Also check your power supply rectifier as well (if you use any bridge). Sometimes the power supply doesn't act as they mention on the catalog.
Sure. i will look in to this..
 

MisterBill2

Joined Jan 23, 2018
12,448
Max is correct. It is most likely an affect from the relay coil circuit, rather then from the contacts. A quick and eady way to know is to remove power from the 230 volt circuit and run the program to operate the relay several times. If the problem remains then it is in the relay coil side of the circuit.
BUT it may also be in the control software or even in the processor power circuit.
 

crutschow

Joined Mar 14, 2008
30,147
The 1N4148 diode datasheet specifies that the maximum forward bias current is only 200 ma.
The 1N4148 diode has to carry the coil current for just the few tens of ms it takes for the coil magnetic field to collapse, and the coil current is likely well below the diode transient peak current rating, so I would think that is not a likely cause of the problem.
The transient voltage from that is less than a volt (the forward diode drop)
 

MisterBill2

Joined Jan 23, 2018
12,448
Let me clarify the issue. It is more probably a power supply problem, NOT a relay coil transient problem. If the relay is adequate for controlling a 230 volt fan, the coil current is great enough to load down the power supply and that is why the control processor locks up. That has been a problem with a number of control schemes discussed on this site.
It might even be a software problem.
So the first diagnostic step is still to remove the 230 volt fan power and see if the lock up problem remains.
 

Thread Starter

ep.hobbyiest

Joined Aug 26, 2014
201
Okay. I will test the board without any AC load.
In the software I am just turning it ON and OFF. I think the issue is more likely in the relay circuit or may be related to isolation.
 
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