Hello everyone, I wanted to know if there is a way to determine the RPM of an electric motor using the controller that I will link below. I have noticed that there is no output cable that reports a speed value. The only thing that came to mind is the possibility of using the green cable that is part of the connector to connect to the LCD display (which shows the speed in km/h, so there should be information related to the speed of the motor), but I am not sure how to use this signal and how to understand what type of signal it is.
Thanks in advance!

Controller (48V, 800W): https://it.aliexpress.com/item/3270...151214375!sea!IT!0&curPageLogUid=3b23dF9BZWLZ

 

Why do you require motor RPM?
Obviously it would be a direct ratio of the motor rev to revolution/distance of the e-bike wheels.?

 

Why do you require motor RPM?
Obviously it would be a direct ratio of the motor rev to revolution/distance of the e-bike wheels.?

I am using the motor for an application which does not require the rest of the e-bike, so I don't have any wheel. I was wondering if I can be able to measure RPMs of the motor using the output wires of the controller I linked above.
Thanks!

 

The page for the Controller states that there are 2-versions of the Controller,
one has a Connector for the LCD-Display, and one does not have the Connector.

The Controller can be purchased as a "package" with the Controller/Display included together,
and, the Display is also available separately.
But, if You already purchased the Controller,
You must check to see if the Controller that
You have received has the correct connector for the Display.

The Display provides all the information that You could want.
.
.
.

 

It wouldn't surprise me if there was a speed output from the controller, but maybe you can get a signal from the wiring between the motor and controller.

 

In principle, any one of the three hall sensor outputs could be used to calculate motor RPM.

 

In principle, any one of the three hall sensor outputs could be used to calculate motor RPM.

How can I use the signal form one of the three Hall sensors in order to get the rpm of the motor?

 

First you need to find out how many poles it has, short all three leads together and turn it slowly and count the 'Bumps' per rev.

 

Probably it is possible to pick up enough signal to operate a frequency counter simply by wrapping a wire around one motor fiels lead, with no electrical connection, thus assuring no damage to the driver. Then it should be simple to determine the RPM based on the frequency. The clear benefit is no damage or modification to the motor system.

 

Probably it is possible to pick up enough signal to operate a frequency counter simply by wrapping a wire around one motor fiels lead, with no electrical connection, thus assuring no damage to the driver. Then it should be simple to determine the RPM based on the frequency. The clear benefit is no damage or modification to the motor system.

The pole count would still be required for this method also!

 

RPM's can be read by an old early BLDC motor chip, the MC3309. You may want to look into it. No pole count needed, it works by reading the Hall position sensors.

https://www.onsemi.com/pdf/datasheet/mc33039-d.pdf

 

But you still need to know how many poles the motor has in order to calculate how many hall pulses represent one revolution. If using a hall sensor for RPM rate.

 

But you still need to know how many poles the motor has in order to calculate how many hall pulses represent one revolution. If using a hall sensor for RPM rate.

How do you mean? There are only 3 hall sensors for the motor, so that means it takes 6 pulses for one round of the shaft. No matter how many poles involved, there isn't, as far as I know, a Hall sensor for each pole. And there are only 3 phases involved, no matter how many poles in the motor.

 

Yes but more poles mean more pulses/rev.
I have converted quite a few BLDC motors to encoder commutation tracks, these encoders have the commutation tracks, equivalent to the Hall sensors, on them as well as the normal quadrature signals.
You have to order the correct commutation track which depends on the amount of motor poles, IOW, the position of the tracks on the encoder.
I would short the three power conductors and turn the motor 1 rev and feel the bumps, This trick I learned from Renco where I used to order all my encoders from.
The encoder then had to be aligned to the pole positions using a double beam scope with the motor being back fed/rotated ~ 100RPM , the commutation tracks were then aligned with the resultant generated sinewaves from the stator.
The encoder method is very much more precise than the old Hall effect versions.

 

The pole count would still be required for this method also!

Often the pole count can easily be determined by counting the number of resistance to rotation instances while manually rotating the motor. This works with motors that include permanent magnets. The other method is to actually measure the RPMs of the motor and also read the frequency at the same time. The ratio will be some multiple of three, which can then be used to select the scaling value.

 

Just an update to my last post, just in case anyone should also need to align optical commutation tracks,
When aligning the track with the selected track output and its relative phase using a DB 'scope, the phase selected has to be relative to the neutral point, which generally is not available.
So a virtual N has to be set up using a 10k resistor from each phase with the outer ends of the three joined together, this point then becomes the relative N for the scope gnd lead for that input.

 

Often the pole count can easily be determined by counting the number of resistance to rotation instances while manually rotating the motor.

See post #8, also #14, already mentioned.
Also I do not know of any modern BLDC motor manuf. in the last 30yrs/40yrs that has anything but P.M. poles on the rotor!

 

I have converted quite a few BLDC motors to encoder commutation tracks, these encoders have the commutation tracks, equivalent to the Hall sensors, on them as well as the normal quadrature signals.

That sentence tells the difference. The TS only want's to know speed/RPM not position of the shaft. Being a tree phase motor in reality, the poles are in sets of three, no matter how many poles are involved.

Like if we name the windings 1 -2 -3. If there is more than three poles/windings in the 120degree segment caused by Hall positions, say 6, it would then be 1-2-3,1-2-3.

And if I'm not wrong, the bumps only give the number of magnets, not actual poles.

 

But the poles are the magnets?
And the Hall effect sensors are triggered by the rotor magnets, which can be from 1 pair to 4 pair, typically.
So if you are using the hall as a rev counter, you need to know the number of poles, the higher the number of poles, the higher the number of hall pulses/rev.
This is why when you do fit an optical equivalent to the hall sensor, the number of poles has to be known.

 

And the Hall effect sensors are triggered by the rotor magnets, which can be from 1 pair to 4 pair, typically.

Then every thing I've read about the magnets controlling the Hall sensors is wrong? The 3 PM's signalling the Halls are outside of the magnets in the rotors, on an endbell, is how I read the literature on the sensored BLDC motors. I can't think of the guys name right now but I have a couple of his BLDC motor books, he's a profesor in Scotland. It's too hot upstairs in the house now to go look for the books.

Now if this would be a sensorless BLDC things would be like you say. He said there were Halls, post #7.

EDIT. A Google search showed his name. T. J. E. Miller. https://ethw.org/Timothy_J._E._Miller