Re: [SI-LIST] : DC Motor part 2

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From: Robert Weber (weber@snet.net)
Date: Thu Nov 09 2000 - 20:31:45 PST


Erwin,

No, the back EMF of the motor will not generate that spike in the circuit
you descibed. The armature inductance will not cause it either.

Can you describe how you measured the motor current, and at what point in
your circuit it was measured. Some time scale on the waveform would be
helpful.

Bob W.

-----Original Message-----
From: SEOW,ERWIN-SP (HP-Singapore,ex1) <erwin-sp_seow@hp.com>
To: 'si-list@silab.eng.sun.com' <si-list@silab.eng.sun.com>
Date: Thursday, November 09, 2000 9:28 PM
Subject: [SI-LIST] : DC Motor part 2

>
>Hi all,
>
>Thanks for answering my questions about the DC motor. Attached is a sketch
>of the current waveform that I am seeing in the motor.
>
>1)The first spike is due to the low resitance in the motor (No back EMF)
>during start up.
>2)The current settles to an almost constant value when it is turning.
>3)When the motor is tured off, the armature's inductance will cause the
>cureent to flow in the same direction for a short time until the energy is
>dissipated.
>4)Does this mean that the negative current spike that I see is due to the
>back emf of the motor?
>
>Appreciate the help!
>
>Erwin Seow
>email: erwin-sp_seow@hp.com
>
>

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