Force Guided Relays

STEMAPPLICATIONS

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STEMAPPLICATIONS
Join Date
Sep 2008
Location
Alberta
Posts
40
Did anyone every notice that you can't get AC coils on force guided relays (EN50205) ?

I've read quite a few specs including excerpts from EN50205 but have yet to come up with an answer why they are all DC coils.
 
DC coils have a predictable mechanical force because the field strength is a function of the applied voltage and the resistance of the coil winding. AC coils rely on the impedance of the circuit, which varies with the stroke length. So if something hangs up the armature on an AC coil, the current increases and the magnetic force does along with it.


In a force guided relay, you are "guaranteeing" that if a contact welds, the other contacts in the relay cannot possibly change state, because the force it would take to overcome the welded contact is not there. The predictable pulling force of the DC coils then allows that "guarantee". With AC coils, the coil would start working harder and may break the shaft on the welded contact, allowing the other contacts to change state.
 
jraef said:
DC coils have a predictable mechanical force because the field strength is a function of the applied voltage and the resistance of the coil winding. AC coils rely on the impedance of the circuit, which varies with the stroke length. So if something hangs up the armature on an AC coil, the current increases and the magnetic force does along with it.


In a force guided relay, you are "guaranteeing" that if a contact welds, the other contacts in the relay cannot possibly change state, because the force it would take to overcome the welded contact is not there. The predictable pulling force of the DC coils then allows that "guarantee". With AC coils, the coil would start working harder and may break the shaft on the welded contact, allowing the other contacts to change state.
Click to expand...


Great explanation, that makes perfect sense. You (and many others) always amaze me with how much you know. Thank you for being part of this forum.
 

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