A question regarding BLDC motor control

[Toneboy1]

Ahh, I've been looking for ages how to post since registering.

 I would like to post a question regarding BLDC motor control, specifically I have a few questions about using Hall Sensors.

LONG FORM Question:

I have purchased one of those chinese BOMA motors (supposedly 1800W) 48VDC. I did not purchase the controller for this, as I am building one myself out of an Arduino and possibly a raspberry pi (and three mosfet H-Bridges). There are 5 Hall pins in the control plug. I asked the ebay seller and they said that the Hall sensors are 48 - 54V between the Red and Black. However, this seems quite high, because everyone seems to think they should be about 5V. I supplied 5VDC and looked at the output of the motor when I spun it on my oscilloscope, but I didn't really see anything resembling a square wave coming off the hall sensor output.

Does 48-54V seem like a reasonable range for such Hall sensors?

Thanks!

P.S. Also, regarding the three binary bits coming from the Hall sensors, the switch combination that these bits relate to, is this for the current/present switch positions/states (i.e. the current magnetic arrangement)? Or the next switch positions/states to be triggered?
To re-phrase it another way, regarding the attachment picture of the time table for BLDC control. I'm not sure if the high/low pattern of H1, H2 & H3 are telling the motor what the Mosfets states ARE NOW or what they SHOULD BE on receiving the three bits.
This is to say, the switch states for the phases in the table are Prescriptive, rather than Descriptive?

[Bikemad]

Hi andto the forum.

48-54V does seem to be very high for a Hall sensor power supply as all the BLDC motors I have come across all use the same +5V supply for Hall Sensors.

I would expect the Hall sensor signal to directly relate to the current position of the motor. This article describing how to control a 3-phase brushless DC motor using a GreenPAK and this article regarding the Rotor Position Identification for Brushless DC motor may be of interest to you.

Alan
 

[Toneboy1]

Hi and thanks Alan,

So I swapped the 5V linear regulator out for a buck converter, and just used a multimeter and rotated the motor by hand.

The sensors seemed to work for a buck output voltage of 3.3V. However, curiously the voltage from the Hall sensor was about 4V! Higher than the input.

I was thinking, couldn't I just use 3.3V from the buck converter, and put a 3.3V zener diode across the output to clip it when it get's over 3.3V? (Thus protecting the micro-controller.)

I'll update the thread when I make some more progress (probably after Christmas).

Cheers,

Rob

[Natsukawa]

Hi Toneboy1

I think something is not right, in most cases bldc motors have open drain latching type hall sensors and (but you need the part number to be sure)
this means they can sink current and that means you need some resistor to pull up the output pin to vcc.
https://maker.pro/storage/TBZKhU8/TBZKhU8Z8FF6wyMLYP1LihfoRMAxQluGfzHMZK5W.jpeg

And yes 48-54V is far to great, in most cases they can go up to 24-35 ish voltage.

I'm thinking the same (make one controller), but I will go with some Microchip Dspic (they are fast and powerful)
I recommend to read Application Note AN957.pdf
http://ww1.microchip.com/downloads/en/appnotes/bldc%20mc%2000957a.pdf

The hall sensors output represents the current state, if change is happening that tells the controller to make the next step in the commutation.

[Toneboy1]

Hi Natsukawa,

Thanks for the great reply!

Why do you say something doesn't sound right? Because the voltmeter was saying 3.3V or 5V (approximately) depending on how I had the buck converter output set. And going to zero as I rotated the motor shaft.

So if it has the 10kOhm resistor built into the sensor on the motor (unlikely?). Then while the Hall sensors are open circuit, I should be able to put an Ohmmeter across the digital output and the +5V, and measure around 10kOhm?

Otherwise, if it's significantly higher (or OL) I'll need to incorporate the resistor in my design.

What do you like about the Microchip Dspic?
Thanks for the AN957 resource, I'll look at it over the Christmas break. But what are you using as your three phase inverter?

I know the Hall sensors relate to the current state of the rotor, however, my question relates to how the state of the hall sensors correspond to the state of the MOSFET switches. I.e. as the hall sensors become their current values, do the switches then become the state as shown in the corresponding row of the table? Thus, the switches are in this state for the duration of the Hall sensors being in the corresponding position. I think so and I think I am just over thinking it.

Cheers

[Natsukawa]

Hello Toneboy1,

I’m happy to help with my limited knowledge

"Why do you say something doesn't sound right? Because the voltmeter was saying 3.3V or 5V......."
Nope
I said for the following  " output voltage of 3.3V. However, curiously the voltage from the Hall sensor was about 4V!"
If you feed it stable 3.3V you don't get 4V out if there is a 10k pull up resistor, but foremost you should get the datasheet for the hall sensors.
Example: SS40A (Honeywell)
Supply voltage:    Min 4.5V    Max 24.0V
As you can see 3.3V is a little low, it is possible that it can work, but how stable... is another question.
Arduino is running from 5V why 3.3V or is it a BluePill?

Yup you should measure across vcc and out pin if there is 2.2K-10K ish resistance then good, if open circuit or mega ohm range you need to pull up , (in most cases the controller has the built in pull up resistors).

Dspic is fast and powerful with the Arduino you can run in some trouble with the adc speed, if you need to measure current, but you can get around it. I highly recommend to watch Great Scott's Make your own ESC, or another good source for Arduino is Electronoob's channel.
And its a good practice to get some buffer ic's between micro controller and the inputs, but zener is a way too.
 

https://www.youtube.com/watch?v=W9IHEqlGG1s
https://www.youtube.com/watch?v=NXkLydhRvS0
https://www.youtube.com/watch?v=YV-ee8wA5lI&t=376s (Hall sensored one)

Three phase inverter? You mean the three half bridges? Hmm I'm torn between IGBT's and Mosfet's.
I was thinking going higher with battery voltage....higher voltage lower amperage less heating, higher efficiency.
But IGBT's are not cheap... so not sure yet

"how the state of the hall sensors correspond to the state of the MOSFET switches" you should watch the videos, Great Scott is far better at explaining as I am.

Have a nice day ^.^

[Toneboy1]

Hi Natsukawa,

Good to hear from you.

For reasons unrelated to this project, I want to put the Hall sensors into a raspberry pi, and not an arduino. However, if forced to, then I will. In which case the maximum Hall voltage will be 5v and not 3.3v, you're right.


Can you buy a half bridge, or do you have to make one yourself? If it were me, if I could use MOSFETS over IGBTs, then I would, but I am no expert. If you are buying a half bridge, what product are you considering?

I will follow all these links and follow up the information you have provided, over the Christmas break; thanks!

Cheers,

Rob