Magnetic blowout on relay contacts
Magnetic blowout on relay contacts
(OP)
I have a request for supplying a 30A relay with a "magnetic blowout" option on the contacts. Does anyone know why someone would ask for that feature? I suspect that it is for faster arc quenching, but what kind of application would make that be so important on something so small? I have asked the user and he has no idea, the original design decision process is unknown, all we know is that it is being used on a small DC motor.





RE: Magnetic blowout on relay contacts
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: Magnetic blowout on relay contacts
RE: Magnetic blowout on relay contacts
But it appears as though they don't really need it since they are only switching 24VDC. They may have selected it anyway just for reliability, but that is the information that is lost in time unfortunately. That may come back to what you said Keith,; experience... the harshest of teachers.
RE: Magnetic blowout on relay contacts
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Sometimes I only open my mouth to swap feet...
RE: Magnetic blowout on relay contacts
It is my understanding that:
[a] ‘Blowouts’ are generally used to break the arc upon contact opening.
[b] Basically, the nature of the arc will be determined by the circuit, contacts & atmospheric conditions.
[c] When there is sufficient energy in the system (usually inductive), the energy is dissipated, in the form of an arc, across the opening contacts.
At low voltages (6-48V) and a given load (W), the relay may be designed with a contact/air gap sufficient enough to break the arc when the contacts open. When the same relay is required to switch greater loads, or when the voltages exceed 48V, ‘magnetic blowouts’ can be added to increase the effective air gap. If the magnetic field is aligned correctly, the arc will be bent outwards, and when the length of the gap is sufficient enough to break to arc, the material in the arc will be blown outwards (thus, called blowouts). Of course, if the magnetic field is the wrong way around then the arc will be blown inwards and this can destroy the relay.
The small added cost of the ‘blowout’s may double, or more, the life of the contacts/relay – load dependant.
My comments above are related to DC applications.
Regards,
RE: Magnetic blowout on relay contacts
RE: Magnetic blowout on relay contacts
RE: Magnetic blowout on relay contacts