noise filtering

hi there
i have been having some problems with one of my Arduino freezing or resetting (watchdog) i have been doing some testing with it and the code is fine, the reason is in the box with the Arduino is an contactor (24v DC fed from a power supply in the box) switching 3 phase and every 3-5 times the contactor comes in the Arduino freezing or resets, the contactor is not switched by the Arduino, but the Arduino does pick one of the phase for its power, i have put a suppressor on the contactor coil and still no difference.

The power supply on the PCB with the Arduino:
power supply:
VTX-214-006-112
Voltage Regulator:
L7805ABV
Caps:
33uf Aluminium Capacitors
100nf Ceramic Multilayer Capacitors
1nf Ceramic Multilayer Capacitors

then to the atmega328p

can you see anything wrong or what could be an issue or something else?

Thanks Joe

What happens when you disconnect the 3 phase power from the contactor?

Your text description is not clear to me. Please provide a schematic or a wiring diagram showing EVERYTHING. A hand drawn schematic that is scanned and posted would be satisfactory.

What is the 328 doing ? what is connected to it, ie input switches, sensors etc.

How long are such wires ?

As well as power line interference you can get air born interference.

What kind of current is being switched by the contactor ?

When you say Ardunio, the Atmega 328 , are you refering to an Ardunio board or your own 328 circuit ?

If the latter is it on a pcb or breadboard etc.

A circiut diagram and picture of inside the box might help.

What happens when you disconnect the 3 phase power from the contactor?

i have not dun this will do it tomoz and get some pics

What is the 328 doing ? what is connected to it, ie input switches, sensors etc.

it is monitoring a pipe temp and switching 3 relays on and off
so 1x DS18B20 and 3 relay

i have disconnected the ds18b20 and to out going from the relay and still have to same problem.

As well as power line interference you can get air born interference.

yes i'm starting to think if this could be my problem

What kind of current is being switched by the contactor ?

about 7A a phase but start up there will be a high peek

When you say Ardunio, the Atmega 328 , are you refering to an Ardunio board or your own 328 circuit ?

Atmega 328p on my PCB, you will see when i get pics tomoz

You should be thinking shielded cables, shielded metal box for Arduino, and keeping low voltage
side of things well away from the mains high current stuff.

Reset pin is connected?

You should be thinking shielded cables, shielded metal box for Arduino, and keeping low voltage
side of things well away from the mains high current stuff.

done apart from the pcb being in its own enclosure

Reset pin is connected?

yes with a 10k to 5v

some pictures of it:

please excuse the mess above the pcb its from all the playing
and i have tried removing all the cables going in and out of the pcb apart from the power supply and still have to same problem

Thanks All

Cannot see it for sure, but assume the case / back panel is earth bonded ?

Have you got the common mode choke and varistor fitted to the psu input as recommended in its datasheet.

How do the contactors fire, one at a time or all togther, can you identify it as just one causing the problem or all of them can ?

Any unshielded jumper wires on the back of the board, like that little blue one on the front, even something like that could pick up things.

You could bypass your psu and run the circuit from a 12v car battery to isolate any mains line interference .

Cannot see it for sure, but assume the case / back panel is earth bonded ?

yes

Have you got the common mode choke and varistor fitted to the psu input as recommended in its datasheet.

Well this is what i have on the coil of the contactor

How do the contactors fire, one at a time or all together, can you identify it as just one causing the problem or all of them can ?

well there is only one contactor hehe so i'll go with all at the same time

Any unshielded jumper wires on the back of the board, like that little blue one on the front, even something like that could pick up things.

there is no jumpers on the back of the PCB

You could bypass your psu and run the circuit from a 12v car battery to isolate any mains line interference .

the PSU is not powering the PCB just powers the contactor but yes i could try using a battery and see if the nose disappears.

so is this varistor fine for what i am using it for?
Varistor

and is there anything else?

Could go with a larger MOV (20mm disc). Same manufacturer, 275VAC rated.

I think the problem is with contact arcing from the contactor. You have an MOV across its coil, but none across each NO and COM contacts? Might need to add 3 more.

I think the problem is with contact arcing from the contactor. You have an MOV across its coil, but none across each NO and COM contacts? Might need to add 3 more.

so are you suggesting to put 3 between the phase of the out going of the contactor?

Yes, one each phase Line terminal to Switched terminal on the contactor relay.
Caution High Voltage: Connections to MOV needs to be properly insulated, proper terminations needed.