From: Ole Segtnan ([email protected])
Date: Fri Nov 10 2000 - 01:04:30 PST
Hi Erwin,
First of all let me apologize for a mistake in my previous mail: I thought
"back EMF" meant the induced reverse voltage in the armature winding when it
is switched off, but I can see from the other postings that "back EMF" is the
common term for the internal generated voltage in the motor. My mistake,-
blame it on my bad english..:-((
If you substitute "induced voltage" for "back EMF", the text is correct.
Regarding your new question: Yes, the last (negative) spike must be due to the
back EMF (The voltage generated by the motor spinning).
Now I have a question: Where is the return path of the negative current?
Looking at your schematic in the first mail, I cannot see anything that could
conduct it, but maybe there are more components?
I hope I haven't caused too much confusion with the "back EMF" issue!
Ole
"SEOW,ERWIN-SP (HP-Singapore,ex1)" wrote:
> 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: [email protected]
>
> ------------------------------------------------------------------------
> Name: current.jpg
> current.jpg Type: JPEG Image (image/jpeg)
> Encoding: base64
-- Ole Segtnan Phone: +46 (0)70 267 0475 Ericsson Radio Systems email: [email protected] Torshamnsgatan 30B SE-164 80 Stockholm**** To unsubscribe from si-list or si-list-digest: send e-mail to [email protected]. In the BODY of message put: UNSUBSCRIBE si-list or UNSUBSCRIBE si-list-digest, for more help, put HELP. si-list archives are accessible at http://www.qsl.net/wb6tpu ****
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