48VDC UVR coils holding in for too long 2

[CBGUY]

Has anyone ever dealt with DC Undervoltage Release coils taking a long time to drop out. I have never had this problem with AC coils. These should be less than 100ms but are ocassionally hold as long a 900ms. I am thinking residual magnetism, any ideas?

 

[electricuwe]

How does the freewheeling path look like ? To protect the driving contact from arcing or the driving semiconductor from overvoltage there should be something in parallel with the coil. Either an RC-series connection or a diode with a resistor in series. If there is just a diode in series you will suffer from a long delay as the current circulates for a signficant time within the circuit consisting ofcoil and diode.

 

[FreddyNurk]

Might be related, most likely not, but we're starting to experience the same issue with some of our 240V AC UVR coils on our LV breakers. Breakers (as far as I know) are all from the same manufacturer, and are an older model.

Is this a new issue or are your units consistently taking too long?

 

[waross]

There was an old design where a brass rivet was placed in the clapper or armature of a relay or contactor to provide a small air gap in the magnetic circuit. Heavy usage could flatten the head of the rivet and reduce the air gap. The inverse square law of magnetism would then allow the residual magnetism to make the relay or solenoid "sticky". Many years ago someone realized that the air gap did not have to be in the moving part of the magnetic circuit to be effective. Most contactor designs have an air gap somewhere in the core where it will not be affected by the closing impact.
The point is: a reduced air gap may make a relay or solenoid "sticky".

Bill
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"Why not the best?"
Jimmy Carter