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Author Topic: protection from back emf  (Read 7768 times)

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Offline karmaxTopic starter

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protection from back emf
« on: October 16, 2008, 02:36:40 AM »
hi guys.. i want to make a power board for giving power to 6 motors. in this i am using 24v 22A battery. the rating of each motor is 24v,5A. but i don`t know how to protect my circuit from back emf.... if you have any tutorial or any ic that can help me please share here...

« Last Edit: October 21, 2008, 01:46:07 AM by karmax »

Offline ArcMan

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Re: protection from back emf
« Reply #1 on: October 16, 2008, 07:27:07 AM »
You don't need protection from back-emf.  You do need protection from flyback if you are switching your motor on and off (escpecially with a PWM motor drive).  Is that what your are thinking of - flyback?

Offline Admin

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Re: protection from back emf
« Reply #2 on: October 16, 2008, 10:08:22 PM »
Quote
but i don`t know how to protect my circuit from back emf
Which circuit?

If not flyback . . . If you are referring to a microcontroller, it probably requires 5V, right? Regulating from 24V to 5V is a bad idea, better to just use a separate smaller battery to power the little stuff. Just keep your grounds common.

Offline karmaxTopic starter

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Re: protection from back emf
« Reply #3 on: October 21, 2008, 01:49:24 AM »
You don't need protection from back-emf.  You do need protection from flyback if you are switching your motor on and off (escpecially with a PWM motor drive).  Is that what your are thinking of - flyback?

sorry but i cant understand what you mean by ??? flyback ??? so can you tell me in brief

Offline ArcMan

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Re: protection from back emf
« Reply #4 on: October 21, 2008, 08:14:31 AM »
Back-emf is the voltage that a motor produces as it is spinning - the generator action of the motor.

Flyback voltage is a large voltage spike that occurs when you quickly switch off a motor coil (or any inductor).  These spikes can be thousands of volts.  So they must be snubbed with diodes or risk destroying the switching electronics.  Fast-recovery diodes need to be used because the diode is reversed biased when the coil is energized, but must quickly switch to forward conducting to snub the flyback voltage when the coil is de-energized.


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Re: protection from back emf
« Reply #5 on: October 23, 2008, 07:15:59 AM »
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Back-emf is the voltage that a motor produces as it is spinning - the generator action of the motor.
Not entirely correct . . . it occurs only when a motor changes velocity. Having your motor going full speed in one direction then suddenly telling it to reverse will release a huge amount of back EMF :P

(a motor spinning in steady state will never have back EMF)

Offline ArcMan

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Re: protection from back emf
« Reply #6 on: October 23, 2008, 07:36:57 AM »
Not entirely correct . . . it occurs only when a motor changes velocity. Having your motor going full speed in one direction then suddenly telling it to reverse will release a huge amount of back EMF :P

(a motor spinning in steady state will never have back EMF)

I respectfully disagree.  A motor produces back-EMF even when it is spinning at a constant speed.  For example, if you get a DC motor spinning at a certain constant speed and then measure the voltage at its terminals, you will see voltage - the back-EMF generated as the the armature "cuts" through the magnetic flux of the stator.
« Last Edit: October 23, 2008, 07:37:53 AM by ArcMan »

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Re: protection from back emf
« Reply #7 on: October 23, 2008, 07:52:33 AM »
oops I mis-spoke . . . meant to say voltage/current spikes not back-EMF ;D :-[

 


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