AVR-Chat

Can you substitute your contactors with zero crossing solid state relays?

-----Original Message-----
From: AVR-Chat@yahoogroups.com [mailto:AVR-Chat@yahoogroups.com] On Behalf
Of Roy E. Burrage
Sent: Tuesday, January 08, 2008 3:26 AM
To: AVR-Chat@yahoogroups.com
Subject: Re: [AVR-Chat] Dealing with 3-phase contactor sparks - Practical
approach

Behrooz,

The problem with rfi/emi is that it's more of an art than a science.  
Not only do you have a static (voltage) component, but you also have a 
magnetic component...there is conducted and radiated component.  The 
noise generated is also broad band, which means it has frequency 
components covering a very broad frequency spectrum.

I try to do at least the following as general practice:

1.  Separate all signal lines from the power lines.
2.  Do not run control (power/load) and signal lines parallel to one 
another, perpendicular is good if possible.
3.  You should be able to find adequate inductors (chokes) for your 
control lines at about any electronic parts house.  Try Mouser or 
Digi-Key, just make sure you're using one that is large enough to handle 
your contactor coil current.  There are several manufacturers of these.
4.  If you have the money, it might be a good idea to use a transformer 
to isolate your contactor coils from the power lines...contactor loads 
too.  This might be held out as a last resort.
5.  You might also consider putting RC snubbers across your contactor 
coils.  The contactor manufacturer will have information and 
recommendations for this.
6.  Have you thought about your 5 volt relay contacts?  It might be a 
good idea to put RC snubbers across these too.
7.  Your contactor manufacturer will also have recommendations for RC 
snubbers across your contactor/load contacts.

Anything you can do to reduce arcing and sparking across relay/contactor 
contacts will be a good idea.

Since you have your contactors mounted in a separate enclosure, is it 
metal?  Steel is your friend when you're switching high currents, 
magnetic pulse.

Not knowing how far along your design process is at this point, have you 
thought about putting your control (5V) relays in the same enclosure 
with your contactors?  That way you only have low currents in your 
electronics enclosure, which is much easier to protect from 
transients/rfi/emi influences.

Are your electronics mounted in a metal enclosure?

Hope this helps.


REB


behrooz_hariri wrote:

>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.
>
>
>  
>


 
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