In this post we discuss a high current sensorless BLDC motor controller circuit which does not depend on hall effect sensors for initiating the operations rather utilizes the back EMF from the motor for the sequential input
Overview
For proper commutation most 3-phase BLDC driver circuits rely either on a sensor based feedback or from an external 3-phase sync signal, contrary to this our present sensorless high power BLDC motor controller circuit does not depend on sensors or any external signals for operating the motor, rather very simply processes the back EMFs from the motor winding to produce the required powerful synchronized rotational effect on the motor.
Coming back to our present concept, the circuit employs the IC ML4425 from Fairchild, and enables us to operate any type of BLDC motor regardless of whether the motor has sensors or not.
Most BLDC motor today have built-in Hall effect sensors which provide the necessary feedback to the controller circuit regarding the instantaneous position of the magnetic rotor with respect to the stator winding and informs the controller when the relevant power devices needs to be triggered with the precise sequence, this in turn allows the motor to rotate with perfect synchronization and maximum efficiency.
Working without Sensors
Some BLDC motors may be without sensors, and for such motors the BLDC controller is forced to employ an external 3 phase generator circuit for the required synchronized rotation of the motor.
However the present 3 phase sensorless BLDC controller eliminates all these hassles, and neither depends on sensors nor any form of external triggering, instead the system extracts the back EMF pulses from the stator coil of the BLDC motor for executing the rotational momentum on the connected motor.
This feature allows the controller to be universally used for all types of BLDC motors without going through the complications of the sensor connections or the external 3 phase generator stages.
Moreover since the full bridge circuit power devices are externally configured allows the system to be used with even high power BLDC motors without any restrictions whatsoever. One can simply change the rating of the power devices as per requirement and achieve the intended high current BLDC operation as per preference.
The following diagram shows the complete design layout of the proposed sensorless BLDC controller using back EMF as the triggering source.
Circuit Description
The system looks pretty straightforward, you just have to solder the shown components in place and quickly start the BLDC operations. It is as simple as switching ON power and seeing the BLDC motor rotate with full efficiency.
The controls are also very easy to understand and implement, the RUN/BRAKE switch enables the motor to continue running as long as the switch is in the OFF position, or not grounded, while the motor is instantly stopped as soon as the switch is toggled at the ground level.The POT R18 allows the user to control the speed of the motor linearly, simply by moving the pot knob across the specified range.
Main Advantage
The biggest advantage of this 3-phase sensorless BLDC controller is that it does not require the messy sensor based feedbacks from the motor, neither depends on a 3-phase sync signal from the an external source. As can be witnessed in the above diagram, the feedback is achieved from the motor's main 3 phase operating wires via R8/R9/R10 into the designated pinouts of the IC.
This allows the controller to be used with all types of BLdC motors whether or not a sensor is available. If sensors are available from a BLDC, those can be ignored and the motor may be configured without the sensor wires, as indicated in the above diagram.
Nice one , I love the simplicity of the circuit , thanks for your selfless great input and contribution .
Thank you Rashaka!
Has anyone tried this successfully? If so what was the maximum power rating you could do it for? Please let me know as i need help in this.
Thanks
The design is taken from the datasheet of the IC, which means it is a thoroughly tested and proven design. It will work without fail if everything is done correctly and exactly as shown in the diagram. The MOSFET number is not critical, other variants can be tried with identical specs.
The power will depend on the MOSFET rating. For example if the MOSFET is rated at 200 watts then the circuit will support up to 200 watt load. The MOSFETs must be mounted on suitable heatsink.
Hello Swagatam,
I am interested in the Sensorless BLDC Motor Drive. Can someone make the same for me as I will not be able to do the same because I am not a technical person.
Thanks,
Sachin.
Hi Sachin, I am sorry, it won’t be possible for me due to work load. However, since the above design is taken from the datasheet of the IC so you can rest assured it will work without fail if done correctly. That said, normally all circuits will have some minor issues initially, which will have to sorted out carefully, or else even a small mistake from the constructor can prevent the circuit from working or even cause permanent damage to the parts.
It’s OK? With this controller, can I use a modified engine alternator, creating a system to power the field coil? Thanks.
Sorry, I have no idea about it because not an automobile expert, you will have to consult a qualified auto mechanic.
Hi friend ,
I need to run the 48v 1000watt BLDC motor with out hall sensors so please provide the details for the same.
Regards,
Gopal
Hi Gopala,
You can try the above circuit or the following one:
http://pdf.datasheetcatalog.com/datasheet/MicroLinearCorporation/mXrtruz.pdf
Hi Swag,
im a RC model aircraft designer/builder. My latest thing is designing/building working hydraulic systems for my projects. For the pump I have been using miniature fuel pumps intended for model turbine engines. These pumps are very expensive (around 500$) and all use brushed DC motors.
I have found a source for pumps/motors in China that are much more reasonable in price and quality is higher but they all use a 3 phase brushless DC outrunner motor. The motor controller for these units must be plugged into the airplanes receiver. Where can I find a three phase DC motor controller that doesn’t use the airplane’s receiver. One that would allow me to simply toggle a switch to turn the pump motor on/off.
Hi Robert, If you are looking for a 3 phase DC motor controller which can be switched ON/ OFF independently with a switch, then you can try the concept discussed in the above article.
Or you can also try the 4rth circuit from this article:
https://www.homemade-circuits.com/three-phase-inverter-circuit/
sir
r8,r9,r10 resistor vale send me
Please check the following datasheet, you will find the answer under “Back EMF Sampler”
https://www.homemade-circuits.com/wp-content/uploads/2018/08/ML4425CP-datasheet.pdf
Is the circuit above be use to a fisher pykle direct drive motor if i use 12 to 24 v input. Do you have an idea on how many amp needed to drive the motor. Or do i have to modify the winding to be driven by 12 or 24v
Hi, sorry I do not have any information regarding the specified washing machine motor.
How do I figure out the bootstrap capacitor size and capacitor C13 size?
Cool. Found an ML4426 that has a reverse feature…
pdf1.alldatasheet.com/datasheet-pdf/view/75735/MICRO-LINEAR/ML4426IS.html
yep that’s cool, thanks for updating, appreciate it.
I looked everywhere. Where can I get the ML4425 or similar chip?
I think you can find it on ebay….
Thank you for all these great BLDC motor control projects. I have been looking at theses circuits for a while and can’t see how to apply reverse to any of them. Can you explain how reversing the rotation would work. I would really appreciate the explanation.
You are most welcome, it can be probably done by swapping the set of signal inputs either from the sensors or through back emfs that arrive from the Motor to the IC
Thanks again,I was thinking along these lines. Very much appreciated…
you are welcome!
Ml4425 is obsolete. Alternative?
unfortunately I could not find any similar high power alternative so far.
thanks alot sir let me do that
gud day sir i am studing this circuit i want to use it to run my motor but all the transistors and fets listed are sueface mount type yet i want to use these ordinary ones.and also can i run it at around 120v and 1.2kw what should i add thanks sir.
Hi Olupot, the mosfet an BJT values are not critical, you can replace them with any other equivalent which may be easily available in your area….
120V operation may not be possible without a converter, because the unit is designed to work with 80V max