Questions tagged [back-emf]
The back-emf tag has no usage guidance.
89
questions
2
votes
2answers
49 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 ...
4
votes
3answers
100 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
votes
1answer
55 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
vote
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
votes
3answers
84 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
304 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
vote
1answer
62 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'...
2
votes
0answers
69 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
vote
0answers
106 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
vote
2answers
440 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
votes
1answer
195 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
votes
0answers
100 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
vote
0answers
32 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
votes
0answers
50 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
vote
0answers
44 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
613 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
votes
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
vote
2answers
211 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
465 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 ...
1
vote
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'...
0
votes
0answers
58 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
vote
0answers
397 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
votes
0answers
303 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
votes
0answers
261 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
votes
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
votes
2answers
194 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
179 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 ...
1
vote
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
votes
3answers
432 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
votes
1answer
326 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
251 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
votes
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 ...
-2
votes
2answers
266 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
vote
1answer
576 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
votes
1answer
198 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
743 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
votes
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
votes
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
votes
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
votes
1answer
355 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
votes
0answers
465 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
votes
1answer
222 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
votes
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
votes
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
votes
2answers
312 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
votes
1answer
573 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
187 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
717 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
915 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 ...
