AVR-Chat

----- Original Message ----- 
From: "behrooz_hariri" <behrooz_hariri@yahoo.com>
To: <AVR-Chat@yahoogroups.com>
Sent: Tuesday, January 08, 2008 9:53 AM
Subject: [AVR-Chat] Dealing with 3-phase contactor sparks - Practical 
approach


>
> Problem:
>
> Industrial contactors make such a high noise (surge) that occasionally
> cause these symptoms on AVR MCU :
>
> 1- LCD blink,  unrecognized characters
>
> 2- Flash rom bitmap change
>
> 3- EEPROM change or erasure
>
> Explanation:
>
> My atmega16, controls 3-phase contactors
> <http://en.wikipedia.org/wiki/Contactor>   through 5V relays which are
> using ULN2803. As chokes,  I wound about 10 turn of  wire over a 8mm
> diameter ferrite rod taken from AM radio antenna.  So, MCU commands to
> ULN, it activates 5V relays, and after the rod choke, contactors (in
> another metal case) are trigged.  I used the same (one) rod for all
> input/output lines in controller box. This made the situation much
> better, yet I get the same problem after 100-200 cycle of contactor work
> (for exaple after a 5 hours of work).
>
> My Understaing:
>
>  I guess when 220V AC sine wave gets it peack, and contactors is
> released at the same moment, the maximum spark is created and it
> reflects back through the output wire to MCU. Maybe some radiowave is
> also made, so I put the whole 220V contactors in a seperate metal case.
>
> Question:
>
> 1- What is the real frequency of this noise/spark/surge, and its
> voltage? If I know it, I can manage to attenuate it to tolerable level.
>
> 2- How can I improve the situation? Maybe a low-pass filter do the job
> (or complete the isolation)?
>
> 3- Is there a web link to information regarding contactor surge
> reduction? I couldn't find any.      I probably can not find commercial
> surge killers, so please teach me how to make one with electronic parts.

AVX TransGuards.

Leon