[SOLVED] Back EMF from relay resets MCU

[samuelr]

Hi

I have a problem with back EMF from a relay. But when its not connected to the 220V devices the MCU will not freeze. I have tried using snubber and diode combo to try to cut it down but there is still the problem persist. I am thinking if I were to sample the current from the 220V line and cut the relay at zero-crossing this might help reduce the B.EMF significantly. Any ideas?

 

[JSCV]

Hello Samuelr,

Nobody will be able to help you without a clear problem description and schematic if possible.

 

[srizbf]

Hi

I have a problem with back EMF from a relay. But when its not connected to the 220V devices the MCU will not freeze. I have tried using snubber and diode combo to try to cut it down but there is still the problem persist. I am thinking if I were to sample the current from the 220V line and cut the relay at zero-crossing this might help reduce the B.EMF significantly. Any ideas?

even after adding snubber and rev diode , if the problem persist, it indicates that your MCU powersupply is not proper.

 

[--BawA--]

Try to use a decoupling capacitors at the VCC pin of your MCU, and place this capacitor near to the VCC pin.

 

[schmitt trigger]

I wish I had a dollar for every time I have read someone complaining that their MCU freezes when switching powerline devices.
There are straightforward ways to alleviate this.
But before we go down a blind alley, please share your schematic, and we will start making recommendations.

 

[walkura]

Let me guess, You are switching an inductive load.
This can be a valve, a standard transformer etc. etc. with a standard relay.
Please tell which loads You try to switch, take pictures of the setup and show how You did it.
If this is the case please also include a clear picture of the layout, 50+% of these cases are layout issues.

 

[dick_freebird]

Is the relay catch-diode put at the relay to keep the
kickback current loop remote? Putting it on the MCU
assembly might make sense BOM-wise or eliminate
a relay-end harness complexity, but would not be
good for spikes in bad places. Don't see offhand why
the problem would be related to line power, other than
maybe a ground (or relay power, if low side switched)
loop involving the line power supply being different than
on the bench.

 

[samuelr]

SOLVED. Actually its just I am using a smaller relay to switch on a bigger relay on the smaller relay there is a diode and snubber it works fine by itself. When I use it with the bigger relay it causes the MCU to freeze. I just added a snubber on that relay and the problem was solved. Interesting. It looks like the isolation on the smaller relay is not that good.

 

[treez]

I remember working at a high power smps place, and whenever someone opened the door on their high voltage test chamber, the safety relay which switched off that HV supply would activate, and knock any power supply that happened to be operating on a bench in that room into a fault mode.