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3 Phase Relay switching motor causing me troubles...

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dandrews

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I developed a replacement electronic control for a product recently.
A 3-phase motor that is switched on/off by a simple relay is causing me some problems.


The control in question has a Z-World Controller with a custom PCB interface.
I thought I did the right things..
-All of the the I/O is ostically isolated from the CPU.
-The Power supplies for the CPU and Optical Isolation Circuits are both power by isolation transformers.

The real problem is there is a shift register on the pcb board where the outputs are getting "scrambled" at times when the knife relay switches on/off.
Iried putting software "refreshing", but an incorrect small pulse when the outputs do scramble is picked up sometimes by external equipment...

any ideas on trimming down noise from this 3 Phase relay ?
 

nandhu015

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Hi

I once faced this type of problem. I was designing a control for generator. There was a swtich which caused the problem. I also had perfect isolation.

1. Put .1mfd on each and every input and output of control unit.
2. Use line filters ( you can see it in commercial smps). Some switching interfernce will pass thro isolation transformers

Regards
Nandhu
 

Vinay1277

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I also have similar work in hand where i have to put auxillary relay arrangement alongwith three phase starters for motors ranging from 5 to 20 HP . Most of the starters are DOL . This auxillary relay arrangement is for automation purpose . Intelligent circuitary will issue control signals to energise relay1 which in turn will make contact with points in green start button of starter this will last moentarily so starter picks up simlarly another relay will work to stop motor by breaking cicuit in control section of starter. I request opinion and experience of those who have done similar kind of three phase motor automation .
 

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