What Are the Effects of Counter-EMF on Electric Motors?

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Discussion Overview

The discussion revolves around the effects of counter-electromotive force (counter-EMF) on electric motors, exploring its implications for current draw, operational efficiency, and theoretical scenarios where counter-EMF exceeds input voltage. Participants examine both practical and theoretical aspects of counter-EMF in the context of motor operation and energy transfer.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants question whether counter-EMF would cause a motor to draw more current, suggesting that it typically leads to a reduction in current draw once the motor is running.
  • There is a theoretical consideration that if counter-EMF were greater than the input voltage, the motor could potentially stop or even reverse direction, with some participants proposing that this scenario could lead to energy being returned to the source.
  • One participant suggests that under certain conditions, such as steep ascents, electric locomotives can generate energy back to the battery, indicating that counter-EMF can be beneficial.
  • Another participant illustrates their understanding by describing how a motor behaves with and without a load, emphasizing the relationship between load, current draw, and counter-EMF.
  • Some participants express uncertainty about the implications of high counter-EMF, with discussions about whether it would lead to the motor ceasing operation or functioning as a generator.
  • There are inquiries about the possibility of controlling or redirecting counter-EMF under specific conditions.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the implications of counter-EMF exceeding input voltage, with multiple competing views on whether this would stop the motor, allow it to operate as a generator, or have no adverse effects. The discussion remains unresolved regarding the theoretical scenarios presented.

Contextual Notes

Participants acknowledge various assumptions about motor behavior, load conditions, and the nature of counter-EMF, but these assumptions remain unverified within the discussion.

  • #31
right

one of the formulas you can derive from that basic understanding is

e = Blv

e = voltage
l = length of conductor
v = velocity of conductor relative to field
B = magnetic flux density

"""after long hours thinking about it...""" bravo !
cross check your microscopic understanding against the formulas in your book and make them meld. Once you have the basic physics imprinted you can derive the formulas with ease, which beats cramming for exams.

old jim
 
Last edited:
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  • #32
jim hardy said:
right

one of the formulas you can derive from that basic understanding is

e = Blv

e = voltage
l = length of conductor
v = velocity of conductor relative to field
B = magnetic flux density

"""after long hours thinking about it...""" bravo !
cross check your microscopic understanding against the formulas in your book and make them meld. Once you have the basic physics imprinted you can derive the formulas with ease, which beats cramming for exams.

old jim

Makes sense!

Because a conductor with many turn's will generate a significantly powerful C-EMF, if there is a small portion exposed to the magnetic field it would generate a weak C-EMF compared to INPUT-EMF,

Thanks Jim! I appreciate all you're efforts everyone thanks!
 
  • #33
When C-EMF is produced - is it true that some of the energy is dissipated as heat - if so is there an equation which can be used to find out how much is lost in heat.
 
  • #34
CGOLDING said:
When C-EMF is produced - is it true that some of the energy is dissipated as heat - if so is there an equation which can be used to find out how much is lost in heat.
The energy losses as heat arise from friction and I2.R losses in conductors (that includes eddy currents in metal). Primarily, it's the I2.R copper losses that are load-dependent; if there is no armature current, these losses are a minimum. The counter emf determines the current, this in turn determines the Ohmic losses.
 

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