Relay Chattering: Causes & Prevention

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Discussion Overview

The discussion focuses on the causes of relay chattering and potential prevention methods. It encompasses technical explanations and specific scenarios related to electrical circuits and relay operation.

Discussion Character

  • Technical explanation, Debate/contested

Main Points Raised

  • One participant mentions experiencing relay chattering in an A/C unit due to pressure fluctuations from a reciprocating compressor affecting the pressure switch.
  • Another participant questions the definition of 'chattering,' suggesting it may relate to frequency or mechanical vibration, and proposes that a bad connection could cause the primary circuit to fail when the armature moves.
  • One participant identifies two common causes of relay chattering:
    • A step current drop in the relay drive coil due to an insufficiently sourced power supply, leading to a cycle of the relay opening and closing.
    • An independent oscillation on the coil (signal side) that is not related to the load.
  • Suggestions for prevention include decoupling the coil drive from the relay load, ensuring adequate power supply headroom, and possibly using local AC coupling capacitors, though caution is advised due to potential complications.

Areas of Agreement / Disagreement

Participants present multiple competing views and specific scenarios, indicating that the discussion remains unresolved with no consensus on the causes or solutions for relay chattering.

Contextual Notes

Definitions of 'chattering' and the specific conditions under which it occurs are not fully established, leading to potential ambiguity in the discussion. The effectiveness of proposed solutions may depend on specific circuit configurations and conditions.

kal22
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What causes relay chattering and what can be done to prevent it?
 
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What are your thoughts? What specific circuit are you working with? Is this homework?
 
I've dealt with a relay chattering on an A/C unit due to the pressure fluctuations of the reciprocating compressor on the pressure switch that pulled-in the relay...

...so this is very situation specific.
 
How is 'chattering' defined? I mean, as in frequency and/or mechanical vibration. If it's really fast, like a buzzer, I'm wondering about a bad connection that causes the primary circuit to fail when the armature moves...?
 
Two common reasons:
1. When the relay 'makes' the new system load causes a step current drop in the relay drive coil due to an insufficiently sourced system power supply. This causes the relay to 'break', the open load allows the coil current to recover closing the relay again an so on. Decouple the coil drive from the relay load to correct: more head room on your system power supply, separate power for coil and load (usually is anyway for a relay - that's the point) or better local AC coupling caps (careful - can be complicated as you can just create more problems in a tank circuit w/ the coil and caps)
2. A simple oscillation of some kind on the coil (signal side) independent of the load.
 

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