Questions tagged [back-emf]

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4
votes
3answers
95 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 ...
0
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1answer
51 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? ...
1
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2answers
65 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 ...
3
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3answers
64 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....
8
votes
1answer
265 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 ...
1
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1answer
60 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'...
1
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0answers
53 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 ...
1
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0answers
95 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 ...
1
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2answers
240 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
168 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 ...
0
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0answers
81 views

chances of A4988 motor driver creating back current through the STEP and DIR pins

I am trying to drive 2 stepper motors using A4988 motordrivers and I am using the following circuit diagram as shown in the image Only change from the above circuit diagram is that I have not ...
1
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0answers
31 views

Noise on Input Buttons for H-Bridge

I'm constructing an H-Bridge to control a linear actuator. I've done so by using a 2-channel relay module, some buttons, and a ESP32. I do not believe this is an issue of debouncing as I account for ...
0
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0answers
47 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 ...
1
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0answers
38 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
votes
1answer
545 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 ...
0
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1answer
51 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 ...
1
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2answers
200 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 ...
0
votes
1answer
431 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 ...
0
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0answers
48 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'...
0
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0answers
57 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 ...
1
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0answers
352 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. ...
0
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0answers
276 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 ...
0
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0answers
231 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 ...
0
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0answers
52 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 ...
0
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2answers
178 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
votes
1answer
173 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
1k 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 ...
0
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3answers
406 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 ...
0
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1answer
288 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
votes
1answer
244 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 ...
0
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1answer
1k 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
231 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 ...
1
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1answer
539 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 ...
0
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1answer
189 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
votes
1answer
125 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 ...
0
votes
1answer
661 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 ...
0
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3answers
2k views

How EMF is generated in a generator

Classical education of EMF generation usually starts with something like this: Where a wire is placed within a magnetic field and moved to create EMF. Or this: Where a magnet is moved within a coil. ...
-1
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2answers
4k views

Can I calculate the back EMF, motor constants and internal resistance of a DC motor based on these data?

I connected a small motor hub to the gearhead of the motor. Then, I measured the voltage, current and speed of turning using a tachometer. I am not sure if the added weight/inertia due to the 12g hub ...
5
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2answers
1k views

Won't the back EMF from the relays hurt the LEDs?

In this ULN2803 based relay driver schematic, why won't the back-EMF from the relays hurt the relay status LEDs?
0
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1answer
343 views

Extra (diode?) protection for H-bridge to prevent damage - how?

I am trying to use a IMS-1 H-Bridge with a 24V/20A psu and a motor 24V/20A. I already burned one of these H-bridges in one direction and I assume that was caused by a back EMF. Specs of the H-bridge ...
0
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0answers
435 views

Controlling coreless DC motor using ESP8266-01

I want to control a coreless 3.7 VDC motor (quadcopter motor) using a ESP8266-01 module. I've used a BC547 (BJT) to act as a switch for motor. The circuit worked fine with LEDs but when connected to ...
3
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1answer
216 views

RLC circuit: unexpected behaviour

I see some unexpected behaviour from (what I thought) is a relative straight forward RLC oscillator circuit: The idea is that a coil is charged over a certain period of time (during this pulse the ...
2
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4answers
2k views

Driving a fan using a mosfet, do I need a diode?

I am using this BS170 MOSFET to drive a fan using a pwm signal generated by a 3.3V MCU according to the following schematics: (I know about the wrong symbol it's just for the packaging on the PCB) ...
6
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5answers
2k views

“Where” does back EMF appear in motor?

I've been trying to understand EMF, specifically back EMF in electrical motors, such as for example a setup like this: Say that we apply a voltage to the brushes. I understand that once the rotation ...
4
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2answers
291 views

Killing Kickback with capacitors

I am having some problems with an active rectifier (AFE unit) that produces a 8 kHz and a 50 Hz component on my DC. We have bult in a normal standard Low-pass filter that deals with the 8 kHz, so no ...
0
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1answer
537 views

Does SSR with DC Motor still nead back EMF protection

I plan to use a solid state relay to control a couple of small 12 VDC motors. One is 12V, 12Watt (1A) and the other is 12V 11amp peak. The SSR can handle 15A DC. Some of my inputs (different part of ...
0
votes
1answer
179 views

How to Detect Back-EMF from Inductor

I am trying to make a motion detector with a photodiode, and I am trying to trigger a 555 when the photodiode goes from dark to light (this will detect a person crossing the detector, and not stay on ...
0
votes
1answer
684 views

DC/AC motor stall current

I'm getting conflicted information about this so why not ask here. To clarify beforehand: Under DC motor I understand a motor with 2 terminals where you apply DC voltage to get current flowing in 1 ...
1
vote
1answer
879 views

Protection against back EMF

I am trying to build an ignition cut module with an arduino as part of a DIY quickshifter on a motorcycle. I have build the circuit shown below. The points A and B on the circuit fit inbetween the ...
1
vote
2answers
614 views

Brushed motor BEMF ringing

I am attempting sensor-less speed control of a brushed DC motor using PWM and measuring the BEMF (motor-induced voltage proportional to speed). The motor is powered through a H-bridge IC (TI DRV8801). ...