Questions tagged [back-emf]

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34 views

Blackout Protection for H Bridge with Synchronous Rectification

I'm designing an H-bridge motor controller with synchronous rectification similar to the Ti Stellaris RDK-BDC24 link here. Synchronous rectification has the promise of handling the back-emf from a ...
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2answers
38 views

Relationship between torque and back-EMF voltage | BLDC motor modeling

I want to simulate an BLDC motor, so I am studying corresponding mathematical model. My problem is that I am little bit confused by the torque equation. \$e_a\$, \$e_b\$, \$e_c\$ - Back-EMF voltages (...
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0answers
30 views

DC Series Motor Homework Question

A 220V series motor that has a total resistance (field winding and armature winding) of 0.2 ohms and runs at 1000rpm and takes full load current of 200A. The speed of the motor at which it develops ...
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1answer
49 views

Is it must to have freewheeling diodes for ULN200x when used with dc motor?

I need to eliminate the MOSFET drive circuit from my PCB by replacing uln2004 or uln2803, should I still keep the back EMF diode across the dc motor? motor supply 5V current 70mA
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2answers
68 views

Using back emf for charging window-blind controller battery

Let me start: I have no clue of electric engineering. However, I built an automated window blind controlled by my home automation. It consists of a stepper motor, motor controller board, an ESP8266 ...
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2answers
72 views

Operation of Induction Motors and their Back EMF [duplicate]

I'm trying to reconcile the physical steps that go into the operation of an AC induction motor. Looking online, I either find broad and general explanations that I already know and understand, or very ...
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8answers
248 views

Inductor with AC source

When an AC source is connected with an inductor we have a continuous change in voltage and current across the inductor. According to Farady and Lenz law we will get an equal and opposite voltage ...
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0answers
16 views

Peak Recovery Current in Inverter Diode

I have an H-Bridge module comprising four IGBTs with flyback/inverter diodes incorporated [Vincotech FZ074PA075SM] which is intended to reverse a current of around 50A in the circuit to field coils of ...
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2answers
139 views

Why does the measured back-emf decrease when R is shorted in this circuit?

In the following circuit I move an iron rod back and forth inside a solenoid (represented by Rsol and Lsol) and measure voltage fluctuations across the terminals. I do this under two scenarios: with ...
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1answer
100 views

Back EMF protection on bidirectional DC motor controller

I am trying to design a circuit using the TB67H450FNG,EL motor driver ic to control a 6v dc motor that will be run bidirecitonal and run in 1 second pulses. due to being bi directional I am unsure of ...
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1answer
112 views

Solenoid and mechanical damping, options for ways to minimize

I have an iron rod supported by a coil spring that vibrates vertically within a solenoid coil. The solenoid has a 5 ohm dc resistance. There is no physical contact between the coil and rod. As I ...
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1answer
39 views

How do I calculate the regulation of the generator in a Ward-Leonard system?

I have a DC motor with independent excitation, power by a ward-leonard system. The nominal voltage applied to the motor is 250 V. I have to calculate what regulation(%) to apply to the generator so ...
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1answer
54 views

Back EMF in a transformer with an external power source to the secondary coil

When discussing an ideal transformer, Wikipedia says “varying flux at the secondary winding induces a varying electromotive force (EMF, voltage) in the secondary winding due to electromagnetic ...
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2answers
63 views

How do we reduce or nullify the back current from the wheel motors of the modern electric vehicles?

As expected, this EMF opposes the voltage of the source that created it; that is, the motor becomes a generator as soon as it is turned on, and the opposing (or counter, or back) EMF will increase ...
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0answers
30 views

Primary coil of an ideal transformer [duplicate]

My textbook says that when primary winding of an ideal transformer is connected to an alternating voltage, an alternating current flows which in turn produces an alternating flux which causes an EMF ...
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2answers
96 views

Phase difference between resistor and inductor voltage in an RL AC circuit

In my textbook, it is given that \$\mathcal {E} = -L\frac{\Delta I}{\Delta t}\$. The graph of resistor voltage (\$V_R\$) and inductor voltage (\$V_L\$) in a series RL AC circuit is given similar to ...
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3answers
177 views

How is that “howling” sound produced in induction motors?

Note: No, there are no inverters involved in this question here. I've perceived that most, if not all induction motors make a "howling" sound in their coils that is different from the constant 60 Hz ...
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1answer
73 views

Connecting two motors in series [closed]

I have a 240-volt mains supply and I want to run two identical BLDC motors rated at 120 volts each. Without the need for a transformer with just the help of IGBTs and inverter can I run the motors? ...
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2answers
68 views

Why don't motors coupled to gearboxes spike up significantly?

A 5,5KW motor is rated 11,40A for the delta connection at 400V. This motor is coupled to a gearbox that reduces it's speed from 1440rpm to around 121rpm. On the gearbox shaft is a sprocket and chain ...
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3answers
291 views

Is back emf inductance in a ignition coil circuit symmetric for on/off cases?

I was trying to understand how an ignition coil circuit works practically, and came upon this website explaining the behavior of an ignition coil when subjected to changes in voltage: http://www....
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1answer
468 views

Inferring back emf from oscilloscope

I have this stepper motor with unknown back EMF / RPM. There are 200 steps/rev (i.e. 1.8deg step angle), and 8mH "phase inductance", but I'm not sure if that's enough to calculate back EMF. I hooked ...
2
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1answer
170 views

Extracting back EMF from DC motor

As DC motors generate more back EMF, the current that the motor receives drop lower and lower. Now if there were a way to extract the back EMF of that motor out of the circuit (I don't know if that'...
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0answers
125 views

BLDC bemf shape

I am trying to detect the zero crossing point of the BEMF voltage in order to control the motor sensorless. The following picture shows the ideal shape of BEMF and in many application notes or ...
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0answers
183 views

High pass shunt filter

I have a DC motor, which is used as an electromagnetic brake. However I want to leave certain frequencies uninhibited, so I thought this should be possible by adding a shunt filter on the DC motor ...
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2answers
2k views

Relationship Between Number of Coil Turns in DC Motor and the Efficiency of Energy Retrieval From Regenerative Braking

When learning about regenerative braking, I began to ponder as to what the relationship between the number of turns in the coil of a DC motor is to the efficiency of kinetic energy retrieval from the ...
2
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1answer
349 views

Freewheel diodes and shoot-through prevention required on this low-voltage H-bridge?

I have built the following h-bridge: VMOT1 is at logic level (3.3V) FWD and REV are driven by MCU (no PWM in the scope examples given) Q7/Q8 are DMP1045 Q9/Q10 are BSS138 D3/D4 are 4 x 4148 the 2 ...
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0answers
61 views

Back EMF sensorless BLDC control

I am trying to detect the zero crossing point of back emf in a bldc motor in order to control it sensorless. Do you have any idea what detection circuit should I use. I am thinking about a network ...
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0answers
64 views

Wireless DC motor controller circuit protection

I'm using an off-the-shelf 2 channel wireless relay/switch to control a 12 V DC motor. The motor is attached to a wheel which can be manually turned and generate back EMF. How should I place ...
2
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1answer
1k views

BLDC (Brushless DC Motor) vs PMSM (Permanent Magnet Synchornous Motor)

The differences between BLDC and PMSM are very small and for what I have seen while reading about it, is not clear to many of us. Most of the articles I have read say that the main difference is that ...
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1answer
52 views

The inner workings of motors and generators

Inductive components like motor winding resist sudden changes in current. That's because the magnetic field caused by the current needs time to build up or decrease. That means that when current is ...
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2answers
300 views

Can every voltage source accept fly-back diode's current?

A diode is used parallel to the motor (or inductive load) in order to prevent damage to the switch because of back-emf voltage. Now, that back-emf voltage actually produces a current and by using a ...
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1answer
586 views

STM32405 ADC on Update Event of Timer 1 or 8

I'm not sure what I should be asking for because some of the terminology is confusing to me, but what I'm trying to do is use the two motor timers (TIM1 and TIM8) on the STM32F405 to sample BEMF on a ...
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0answers
50 views

BLDC BEMF unequal power-on stage length for different phases

i'm driving BLDC using sensorless method. The driving algorithm is woking fine, but on the bemf oscilogram i can see, that the power-on stage length is little bit different for each of the 3 phases. I'...
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0answers
61 views

Why not detecting zero crossing of the back EMFs in BLDC by software?

I am reading about the state-of-the-art approaches to detect the zero crossing of the back (trapezoidal) EMFs on a 3-phase BLDC for sensorless control. Even digitally implemented, they use various ...
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0answers
547 views

Meaning of motor constants for three-phase PMSM

When looking at three-phase permanent magnet synchronous (brushless) motors, \$K_T\$ and \$K_V\$ numbers are often specified. Also, controllers for these motors typically specify maximum currents. ...
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0answers
364 views

Relationship between brushless coil inductance and back EMF as a function of phase angle

In general, does the inductance across the coils of a brushless motor have the same waveform as the back EMF? That is, if back EMF is sinusoidal, should I expect the inductance to be sinusoidal [with ...
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0answers
354 views

BEMF polarity is backwards

Please take a look at this waveform of a 3 phase, BLDC motor: Check out that rising and THEN falling slope...Pretty nice. Now, take a look at what I'm getting on my motors sensorless resistor ...
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0answers
53 views

dc motor calculation

I'm having trouble with this problem. Suppose the machine was at rest, and a weight of 5 kg was suspended from a horizontal bar of length 80 cm attached to the shaft. What current must be applied to ...
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2answers
261 views

Why does my PMDC motor have spikes in its BEMF?

I have two identical PMDC motors. I ran each of them on a dyno at the same voltage and the same load. They both consumed the same amount of current, yet one of them runs 300 RPM slower. The one ...
2
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1answer
191 views

Is there an actual need for the concepts “emf” and “back emf”?

Given a two-terminal element where you can only measure the voltage across terminals \$v(t)\$ [\$v_{ab}(t)\$] and the current \$i(t)\$ defined as entering the positive [a] terminal, there doesn't seem ...
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2answers
2k views

Equivalent electrical model for induction motor

For those people who are looking for induction induction motor SPICE model, please follow the link LT SPICE tools and applications I'm trying to understand the model characteristics and from the ...
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3answers
571 views

How can i stop DC motors from dropping out my arduino?

I am using a MX1508 DC motor driver module to power a couple of motors with an arduino pro mini as the controller. when i connect the circuit as per the schematic, the arduino resets every so often ...
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1answer
469 views

PWM commutation strategy for Sensorless BLDC

For brushless DC motor, we use 6 step commutation. For voltage control, in each phase, PWM is used to drive the Bridge MOSFETs. And for the sensorless algorithm, Back EMF of non-energised phase is ...
2
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1answer
275 views

Energy dissipation and current decay in this circuit

I have a circuit that looks like this : A 200 A current controlled power supplies delivers the current to a coil (with inductance ~ 5 mH) when the MOSFET is open. The varistor is there to clamp the ...
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1answer
2k views

BLDC Calculation for Back EMF

I have a brushless DC Motor that i am considering buying from hobbyking.com with 2100Kv (RPM/v) i am trying to follow the equation on Wikipedia's motor constants page i have included the equation here ...
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2answers
404 views

How to make this switch to act more realistic in LTspice

A series RL circuit is connected to a voltage source for a very long time and passes 1A constant current.¨ All of a sudden a switch between the voltage source and the RL circuit is opened and the ...
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1answer
795 views

Are these BLDC waveforms making any sense?

I'm trying to drive a BLDC with a microcontroller, a discrete inverter and a sensorless network for feedback. Here's the model I'm using and what ultimatly is my PCBA: I'm driving this thing open ...
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1answer
218 views

Power supply voltage climbs after disconnection

I've got a motor controller for a Bldc and I'm in the process of tuning the controller with both PWM frequency, duty cycle and commutation frequency. Anyway, this power supply is a 30v 10A supply and ...
0
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1answer
133 views

Transformer spike at input supply line

I am using this circuit (please don't go by the design it is just a circuit block, this is not the whole circuit). I have connected a 12V DC at the center of the transformer and this 12V is also ...
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1answer
1k views

How to allow a motor to free spin?

In my circuit my motor terminals are connected to the output of a VNH5019A motor driver https://www.pololu.com/product/1451. When the circuit is no longer powered I want to allow the user to freely ...