3 phase BLDC 48v motor and Optical Encoder help..

Hello guys,

I have a 3 phase brushless DC motor which is 0.35hp and is rated at 48v/6.2A. I have a machine which is using it and I have measured that it sends to it 30V at low speeds and as the speed goes higher, the voltage drops.. Why is this happening?

So I would like to control it with my arduino but I haven't found any readymade speed contoller that could handle the amperage and output 30 volts..

Plus, the motor on its back has a HEDS-9100 optical encoder with a codewheel.

So questions are:

1. Is there any readymade stuff that outputs 3 cables (each for one phase) and can drive my motor?
2. Is it necessary to use the encoder? What are the pros and cons?
3. This optical encoder has VCC, CHA, CHB, NC and ground pins.. I think that the existing board doesn't use the VCC pin right now.. Is there any further reading I could do to understand the function of it and why do I need an encoder? I know that it is used to determine the position of the motor so that you know which phases to turn on but why does it have 2 outputs? Shouldn't it have three?
4. If there is any readymade esc, can it use this type of encoder?
5. Is there any schematic I could use to build such an ESC?

Sorry for the lot of questions but I am kinda newbie to this type of motors..

Thank you!

clubman:
Hello guys,

I have a 3 phase brushless DC motor which is 0.35hp and is rated at 48v/6.2A. I have a machine which is using it and I have measured that it sends to it 30V at low speeds and as the speed goes higher, the voltage drops.. Why is this happening?

Are you measuring 3-phase AC or just DC offset? The DC offset is nothing to do with power delivered.

So I would like to control it with my arduino but I haven't found any readymade speed contoller that could handle the amperage and output 30 volts..

Many chinese electrical bicycle controllers are suitable... Assuming a hall-sensored motor.

Plus, the motor on its back has a HEDS-9100 optical encoder with a codewheel.

Useful...

So questions are:

1. Is there any readymade stuff that outputs 3 cables (each for one phase) and can drive my motor?

answered above

2. Is it necessary to use the encoder? What are the pros and cons?

if you want accurate position control or speed control, the encoder allows a control loop

3. This optical encoder has VCC, CHA, CHB, NC and ground pins.. I think that the existing board doesn't use the VCC pin right now.. Is there any further reading I could do to understand the function of it and why do I need an encoder? I know that it is used to determine the position of the motor so that you know which phases to turn on but why does it have 2 outputs? Shouldn't it have three?

This is an encoder, not hall sensors. It is not designed for commutation, it is an incremental quadrature encoder designed for a control loop input

4. If there is any readymade esc, can it use this type of encoder?

standard ESCs do not use encoders - some use hall sensors for commutation

5. Is there any schematic I could use to build such an ESC?

checkout the various open circuit BLDC controller projects that google will find for you

Sorry for the lot of questions but I am kinda newbie to this type of motors..

Thank you!

Hello,

thank you for your fast reply.. i measured dc voltage accross each phase and a ground point while the motor was working.. Is that wrong?

So assuming that my motor doesn't have hall sensors which it probably doesn't have (do you understand something different?) how does an ESC know which phases to switch on initially to start the motor rotating? And if I can't use the Chinese, what would a solution be for my case?

As for the encoder, what is the output of the two pins, CHA and CHB and how would this translate to useful information? I mean ok you can get pulses per sec and so you know speed but is this what it is outputing?

Thanks again

clubman:
Hello,

thank you for your fast reply.. i measured dc voltage accross each phase and a ground point while the motor was working.. Is that wrong?

its a meaningless measurement. The motor windings see the difference in voltage between
phases, which is an AC signal

.

So assuming that my motor doesn't have hall sensors which it probably doesn't have (do you understand something different?) how does an ESC know which phases to switch on initially to start the motor rotating?

Many ESCs can drive sensorless motors, but not at low speeds under load - they use the backEMF
signal from the undriven phase to estimate rotor position, and backEMF is too small for successful control below some minimum speed

As for the encoder, what is the output of the two pins, CHA and CHB and how would this translate to useful information? I mean ok you can get pulses per sec and so you know speed but is this what it is outputing?

I said incremental quadrature encoder for a reason, you can search on those terms. The encoder
gives relative position (as opposed to an absolute encoder), and uses a quadrature signal.

Thanks again

Perhaps you could actually tell us which motor you have?

Well it is a Lafert motor, type ST63S2 but I believe it is modified because when I search for lafert ST63S2 it says 230V AC but mine is 48V.. So it probably is a special version made for the manufacturer of the machine..

Thats an induction motor, not a BLDC.

Hi,
Can you post a picture of your motor/encoder.
What you could have in that configuration is a servo motor.

Tom.....

Hello,

How can you tell if it is an induction or a BLDC? Please help me understand..

So if I do it like a servo motor, is there any shield or some guide that I can drive it?

This is the motor

And this is the encoder which lies at the back of the motor and has a tiny codewheel spining:

Thank you guys!

Hi,
Sorry , we need pictures that we can read the printing on, and a picture showing the outline for the motor and where the opto connects.

Thanks.. Tom......

I you click on the photo it gets enlarged, but anyways, the label says:

Made by lafert
Type ST63S2 IEC 60034 3~Mot No xxxxxx
Th.CI.F IP54 REF. 3861030302
50Hz Δ/* 48/83V S 2 0.26KW 0.35hp
50Hz Δ/* 6.2/3.6A
2780 min-1 cos φ0.70

End cap removed (note that the codewheel is not visible as it is broken but I have a spare part. It actually turns inside the encoder unit:

Encoder removed:

Inside the motor:

Click on the photos to enlarge them..

Thank you!!

As I said that is an induction motor. It has a squirrel cage rotor. If you search the part number you
find a manufacturer of induction motors, if you look at the nameplate it shows delta and wye voltage
and current ratings.

Cool then.. That's a start! So it is an AC induction motor right?

Can you please guide me how to drive it? Do I need a VFD? Is there any shield ready? Or do I have to make my own?

A VFD for a 3-phase induction motor would be the normal approach, but I'm not sure how common
they are for a 48V winding.

Hi,

I have a 3 phase brushless DC motor which is 0.35hp and is rated at 48v/6.2A. I have a machine which is using it

What is the machine, that uses it?

Tom....

It is like a sewing machine..

So VFD is the way to go? Can't I build one myself?

Hi,
What is controlling its speed at the moment?

Tom....

A board.. I have checked the board and it uses transistors and ICs type IR2112..

So can you reuse that board? It will be a 3-phase MOSFET bridge. Checkout this thread too:
http://forum.arduino.cc/index.php?topic=97508.0

Unfortunately I cannot reuse the board.. I would like to build something fresh..

Read your code on the other thread but do you have any schematics for this code should work with?

Thank you