pic reset sometimes

[Pedro Pinto]

Hello All

In my board i use a pic 18F452 that control two relays. This relays drive two contactors "power AC relays" that drive 3 phase motor for up and down motor movement
That all works, but sometimes when start or stop the motor, the pic reset, the 5v is clean with 0,1uF and 220uF, i tested with brownout disable and it is the same problem
I have changed the reset circuit from the pic with many resistor values that is paralell to the diode and the ESD resistor from the anode from the diode to the reset pin of the pic, the reset 0,1uF have changed to 1uF. With some values it is better but never total elimnate this reseting
What can i make to eliminate the reseting of the pic?

Thanks for any help and sugestion

Best regards
Pedro

[Squibcakes]

Pedro,

For starters you can put a dump diode across the relay to eliminate any Bemf when the relay turns off.

You could also try try putting an opto coupler between the pic and the relay. I remeber seeing a post a while back with some guy trying to run a hammer bell or something and had simialr probs. Do a search on relays in this forum and you should find a few answers.

Cheers
Squib.

[Pedro Pinto]

Hello Squibcakes

The realys are drived by ULN2003 that have the diodes inside, but the problem is not the relays on the board but the contactors that is drived trough the board relay, if i disconnect
the connector for the ac contactors the board relays make it's work and the pic not reset,
The ac contactors are connect to a 3 phase motor but the pic reset also if the motor are not connect to the ac contactors. I hear form a zero cross code solutions with one resistor, do you know about that?

Thanks for any help
Best regards
Pedro

[victorf57]

I had the same type of problem some time back.
Installing opto's on the input lines fixed the problem for me.
Victor

[Pedro Pinto]

Hello Victorf57

All the used inputs are with optocopller

I wiil tomorrow try with a zero cross routine

Best regards
Pedro

[BrianT]

If you are driving a relay which in turn drives a contactor you are probably switching some serious currents. Contactors are notorious for generating RFI because, being mechanical, they make or break anywhere in the mains cycle and can give spikes of thousands of volts if they break an inductive load during a current maxima.

If at all possible replace the contactors with AC solid state relays (SSR). These can be driven directly by the PIC and most SSRs have their own zero crossing logic inbuilt to make sure they only make during a zero voltage crossing or break during a zero current crossing.

If you are stuck with the noisy contactors then you will need ferrite beads and noise supressors on all power and signal lines and an earthed or shielded metal box to house the processor board.

Take special care with off board interconnections such as the leads to any LCD display or front panel I/O switches as these are great little antennae for drawing ambient RFI into your processor board. I have used some woven metal tubular sheathing from WARTH International Ltd to shield I/O leads with great success. Farnell 150-840 is one variant you might look at.

Use a filtered power inlet connector, not just a simple fused IEC inlet and use plenty of 100 uH or larger chokes on the power lines. Make sure the main electrolytic power storage capacitors have ceramic 100 nF capacitors across them. The series impedance of an electrolytic capacitor can be quite high and they provide no filtering above 1 MHz or so.

Keep trying, even all the ways that you think cannot make a difference, as RFI is elusive stuff and is not easily cured by any formula or simple 'capacitor here will fix it' solution.

Good luck.

BrianT

[yu1ol]

Try with varistors or RC network (R + C) in parallel with coil of contactors!

Best regards, YU1OL

[Pedro Pinto]

Hello

Have sucess with varistor parallel to the coil of the contactors

Thanks

Best regards
Pedro