I have noticed a lot of talk on different forums about back-EMF being turned on and off, so I thought I might try to explain that this is impossible!
Back-EMF or electromotive force in its full name is the product of current flowing through a conductor in a magnetic field that produces an opposite voltage to the applied voltage. http://en.wikipedia.org/wiki/Lenz's_Law < Link To Lenz's Law
As can be seen back-EMF cannot be switched on and off. What can be done is to use a clever circuit and measure the back-EMF opposite voltage and then apply this as feedback to the control circuit to adjust the running voltage of the motor. This both assists superb slow running and provides proportional load compensation to the motor drive. Back-EMF feedback features do vary brand by brand however back-EMF feedback operates by sensing load and it then compensates for variances by adjusting power provided to the motor under varying conditions. NO other method of control can match a quality back-EMF feedback decoder for running quality.
With back-EMF feedback enabled, locomotive decoders sense the rotational speed and current needs of the motor and automatically adjust future digital pulses to the motor to maintain a desired speed by increasing or decreasing power available to the motor very smoothly.
Back-EMF feedback can be tuned to increase or moderate its effect and even to allow it to gently turn off as speed increases. It is a VERY clever feature and highly desirable.
The first LGB MTS loco mouse and decoder 55020 made by Lenz had no back-EMF feedback. It was not until Massoth came onto the market with their decoder 55021 that back-EMF feedback became popular. Decoder 55021 back-EMF feedback is CV54, this feedback can be turned on and off but not the back-EMF.
The textbook defines:
When current is flowing through the armature conductor of dc motor, it starts rotating inside the magnetic field of stator pole. As the armature conductors move inside the magnetic field there will be an induced EMF in the armature conductor. This EMF would be due to Faraday law of electromagnetic induction. The direction of the induced EMF will be as per Fleming right hand rule and the induced EMF will oppose the applied voltage across the armature terminals. In other words in dc motor the rotating armature will generate an EMF as it is rotating under magnetic field, in opposite of the applied voltage and this generated EMF in dc motor is called back EMF E[sub:1nbez59x]b[/sub:1nbez59x].
Applied voltage V has to drive armature current I[sub:1nbez59x]a[/sub:1nbez59x] against the counter or back EMF E[sub:1nbez59x]b[/sub:1nbez59x].
Hence, armature current I[sub:1nbez59x]a[/sub:1nbez59x] = net voltage / armature resistance = [V ? E[sub:1nbez59x]b[/sub:1nbez59x] ]/ R[sub:1nbez59x]a[/sub:1nbez59x], where R[sub:1nbez59x]a[/sub:1nbez59x] is the resistance of armature circuit.
Railway42
Back-EMF or electromotive force in its full name is the product of current flowing through a conductor in a magnetic field that produces an opposite voltage to the applied voltage. http://en.wikipedia.org/wiki/Lenz's_Law < Link To Lenz's Law
As can be seen back-EMF cannot be switched on and off. What can be done is to use a clever circuit and measure the back-EMF opposite voltage and then apply this as feedback to the control circuit to adjust the running voltage of the motor. This both assists superb slow running and provides proportional load compensation to the motor drive. Back-EMF feedback features do vary brand by brand however back-EMF feedback operates by sensing load and it then compensates for variances by adjusting power provided to the motor under varying conditions. NO other method of control can match a quality back-EMF feedback decoder for running quality.
With back-EMF feedback enabled, locomotive decoders sense the rotational speed and current needs of the motor and automatically adjust future digital pulses to the motor to maintain a desired speed by increasing or decreasing power available to the motor very smoothly.
Back-EMF feedback can be tuned to increase or moderate its effect and even to allow it to gently turn off as speed increases. It is a VERY clever feature and highly desirable.
The first LGB MTS loco mouse and decoder 55020 made by Lenz had no back-EMF feedback. It was not until Massoth came onto the market with their decoder 55021 that back-EMF feedback became popular. Decoder 55021 back-EMF feedback is CV54, this feedback can be turned on and off but not the back-EMF.
The textbook defines:
When current is flowing through the armature conductor of dc motor, it starts rotating inside the magnetic field of stator pole. As the armature conductors move inside the magnetic field there will be an induced EMF in the armature conductor. This EMF would be due to Faraday law of electromagnetic induction. The direction of the induced EMF will be as per Fleming right hand rule and the induced EMF will oppose the applied voltage across the armature terminals. In other words in dc motor the rotating armature will generate an EMF as it is rotating under magnetic field, in opposite of the applied voltage and this generated EMF in dc motor is called back EMF E[sub:1nbez59x]b[/sub:1nbez59x].
Applied voltage V has to drive armature current I[sub:1nbez59x]a[/sub:1nbez59x] against the counter or back EMF E[sub:1nbez59x]b[/sub:1nbez59x].
Hence, armature current I[sub:1nbez59x]a[/sub:1nbez59x] = net voltage / armature resistance = [V ? E[sub:1nbez59x]b[/sub:1nbez59x] ]/ R[sub:1nbez59x]a[/sub:1nbez59x], where R[sub:1nbez59x]a[/sub:1nbez59x] is the resistance of armature circuit.
Railway42