Help and Advise on Regulating 4A Motor at 12V when Rail is 11- 24V

Thread Starter

mohala

Joined Nov 30, 2017
14
Hello, I hope you are all well.

I have come to a little bit of an issue on my project which uses a 12V BLDC Motor Rated at 4A. The problem is, that the voltage rail of which the motor is connected to can vary from 11V - 24V.
I need the motor speed to be with 11-12V and not to speed up over 12V. The reason being it used for suction and if I keep it between 11-12V then I have a reasonably tight tolerance of the suction and flow rates.

I understand the availability of DC-DC converters such as buck, Buck-boost and regulators. But what would be the most efficient option to use, as my power supply and or battery can at most supply up to 4.5 A. Also taking into consideration EM interference (this is for medical application but I really can't go any further by saying what the application is for)?

I would really appreciate help on figuring out the best method of stopping the voltage supply to the motor from going any further over 12V (going down is fine).

Sorry, its a bit vague, I will try to answer as much as I can with without giving away sensitive information.

I hope to hear from you guys soon

Mo
 

dendad

Joined Feb 20, 2016
3,602
Have you though of just regulating the current?
Have the drivers measure and PWM the current to limit it to a constant value irrespective of the supply voltage.
 

shortbus

Joined Sep 30, 2009
7,916
I would say if using a BLDC motor your going about this wrong. Instead of worrying about voltage use what is normally use for controlling BLDC speed, an ESC(electronic speed control). It uses feedback from the motor to keep it in a set speed, and basically that is what your trying to do with your voltage, but it doesn't work near as good as the ESC. They are a pretty commonly available off the shelf item.

https://en.wikipedia.org/wiki/Electronic_speed_control
 

Thread Starter

mohala

Joined Nov 30, 2017
14
The BLDC already has a built-in PWM controller (which the pin is held low to run at full), our application requires the BLDC to run at 100% all the time, so no need to control the motor just a way for it, to run efficiently and at a set voltage (so it doesn't go over its set RPM)

I thought of an idea of using Li-ion 18V battery and stepping down the voltage for the motor using a Buck converter, from the WEBENCH sim it shows the current to be reduced considerably.
 

dendad

Joined Feb 20, 2016
3,602
Do you have data on your controller? Surely it has a voltage input or PWM input that controls the speed. Use that to set the speed at the lower supply voltage and as the volts increases, the speed should stay the same. Any decent BLDC controller will control the speed over varying supply voltages and loading.
 

Thread Starter

mohala

Joined Nov 30, 2017
14
From my understanding it runs a Feedback pin which would provide 6 pulses per RPM and control the speed with the PWM pin, but we would use the controlling aspect with a MCU, but the non-MCU version the only way I'm seeing to overcome that issue is using a Buck converter.



Mo
 
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