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Bigger flyback surge ... relay with fixed core or relay with moving core?
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calzap:
Two relays with coils of same DC voltage, one with fixed core, one with moving core.  Inductance for moving core coil, with core inside, equal to that of fixed core coil.  Assume no flyback suppression.  Which will have the highest peak voltage on flyback? How will the voltage vs time profiles of the flyback surges differ?

Fixed core relays are more common and consist of  an electromagnet moving a ferrous switch-bar against the force of a spring.   Moving core relays consist of a solenoid moving a switch-bar against the force of a spring.

I suppose answering the questions with regard to the moving core relay might require additional data such as inductance with core withdrawn, dimensions of coil and core, mass of core and velocity profile of core movement.   The situation is one of a coil with a core and current flow.  And then having the core withdrawn by a spring immediately after the current is stopped.

Perhaps an empirical comparison has been done, but I haven't been able to find one.

Mike in California

Edit:   If you want more specificity on the circuit connected to coil, let's make it simple:  A 1000 ohm, non-inductive resistor in parallel with the coil.  12 VDC coil supplied with that voltage.


trobbins:
Perhaps if you lead the way, identify and purchase 2 relays that are directly comparable, and test them wit a scope or peak hold meter.
calzap:
I'll think about it.  Right now my lab is disassembled due to a new floor being installed.  It will probably be quicker to wind my own coils than to use off-the-shelf relays.  The reason is manufacturers seldom, if ever, provide inductance specs on relay coils.   They spec things like voltage, AC or DC, inrush current, sealed current, must close voltage, must open voltage, etc., but not inductance.  I've used my LCR meter to measure inductance on a few, but not found a good match between a fixed core and moving core relay.

Mike in California

trobbins:
I've used relay coils for tone/equalisation inductors - some 12VDC like Omron G2R gave about 190mH, although that was just the coil with the bar effectively glued to the face of the coil core to maximise inductance, as the application is AC not DC.

The energy in the coil will be the current and inductance when energised.  That energy will then transfer to a voltage transient that won't be related to inductance, but rather coil self-capacitance, and any other circuit capacitance (unless clamped by another means).

For a DC relay, the operating DC current, and inductance measurement can be set up using the technique in the linked doc below.

https://www.dalmura.com.au/static/Choke%20measurement.pdf
Zero999:
Measuring the inductance of the coil, when the relay isn't energised, will not tell you the full story, because the inductance changes, when the armature is attracted to the core.

A reasonable estimate of the energy can be gained by connecting a small capacitor in series with the usual anti-parallel diode and monitoring the peak voltage. E = 0.5CV2 Of course there will always be some losses in the diode, so the true figure will be slightly higher.
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