Low cost three phase brushless amplifier

[Troubleshooter]

Thanks Ben.

[T_C]

I was wondering if the list of hardware used in generating the driver was also available and if there was a schematic available to complement the drive1.brd file that is referred to.  In addition I noticed in the photos that a 12V power supply is used power the circuit but the motor is a 48V motor.  Are the board components limited to 12V and would it be better for the circuit to drive a 12V rated motor vs. a 48V motor.  I am selecting a smaller version of the BLDC maxon motor that is implemented in this example and want to make sure I don't mis-size it relative to capabilities of the driver.  Thank you for your generousity in sharing this wealth of information!

Regards

[MissFitt]

Hi T_C,

Unfortunately there is no Bill of Materials that was made for this board. However, you will probably be able to look at the BRD file to see what components were used. Can you clarify  what schematic you are looking for? If you are unable to open the BRD file, a screen shot of it is posted below. 

Also, what pictures are you referring to? Thanks T_C!

Mychal F

[T_C]

Thanks Missfitt,

The schematic would be a general electrical diagram indicating connectivity and part numbers and values.  Eagle generates one in a .sch file I believe but it wasn't part of the zip file provided by Ben.

The photo I am refering to is at https://decibel.ni.com/content/docs/DOC-2386

I am deciphering most of the components used in the drive1.brd file but there are a few were it does not specify the value of the capacitance or resistance or connection types (which I should be able to find equivelents).  In addition in the screenshot you provided:

- is the lower MOSFET the FDP9986 or the FQPF11P06

- although the power resistors on the right are marked as being KH214-8's the vendor that I found had several versions of this and required and additional -R# to indicate the resistance

- The electrolytic capacitor in the center of the board is also missing a value

- I am also not familiar with the 0207/2V resistor and it is lacking a value as well.

Sorry for the simple questions, wish my electronics backgound was a little stronger so that I could figer them out.

Regards,

T_C

[Ben_B]

Let's consolidate conversation threads.  I guess this way it'll be public too so that if we answer your questions then other people can see it in the future (better than trying to dig through my email and way better than my trying to remember again).

To that end, I must admit that it has been quite a while since put together this board.  On top of that, it was my first time to use the EagleCAD tools, and I didn't go about it in the right way.  So there's no schematic file to go along with the board design.  I just jumped right into the board and designed it there.  However, I do have one the driver boards sitting in front of me, so let's see if I can answer your questions...

The lower FET is a F50N05L, which is a low-side FET and is an N-type transistor.  I'm using it to control bus voltage in the system so that I have an extra control input for playing with various control algorithms.

The big resistors are 10W 2Ohm power resistors.  Their actual value doesn't really matter a whole lot, as I'm using them as shunt resistors to measure the current in the phases.  You need to balance resistance (smaller has less affect on the motor), power (function of the Vdc value and the motor you're driving) and measurement accuracy (if the resistor value is too small and the current is low, then your measurement will be in the noise of your ADC potentially).

The cap in the middle is a filtering cap for the 5V supply to the gate driver chip.  It's 10uF to help smooth out the noise generated by the 7805 or any of the other components in the system.

I'm not sure which resistor you're talking about, but I'll assume that it's not the 2k pull-up resistors or the power resistors that you asked about as well.  That leaves the DIP packaged resistor bank.  Basically that's just a set of 9 resistors in one package.  I'm using it as current limiting resistors for the LEDs that represent each FET.

(questions from a previous email)

- What is the function of the three FDP8896 N-Channel MOSFET's lined up on the periferial of the board that feed into the three FQPF11P06 P-Channel MOSFETS in the central portion of the board
- Is there a reason you used a 12V supply in your setup vs. a 48V supply to run the 48V motor (availability?). I'm deciding between basically the same Maxon motor (386660) of varying voltages and was wondering if given the parameters of your design if the 12V version would be most applicable or if the 48V version with a 48V power supply would be suitable.

The three FETs at the top of the board are drivers for the high-side FETs.  The theory is a bit fuzzy in my brain right now, so I'll let you google that instead of my coming up with an explanation that's only 90% right.

This should work for a 48V system, but we picked 12V because it ran cooler and slower.  I want to say that there were some stability issues at 48V, but I don't remember if that was this revision of the board or a previous one.

~Ben

[T_C]

Ben,

Thanks for all the information!  I hope I didn't take you too much away from your other obligations.  I would like to order the motors this week and based on your final response it appears you had some experience with this driver at the various voltages so in you experience would you recommend a 12V system or the 48V system or an intermediate voltage and is there some current limitations that I should be mindful of.

Thanks again for all your help!

Regards,

T_C

[Ben_B]

In general, I think 12V is easier to work with.  I get a little leery tinkering around with things over 36V.  We picked that motor specifically due to its slow time constant.  We wanted to be able to spin it in a range that we could see the LEDs flicker (not actually see the PWM signals but see the PWMs changing over time as the motor rotates through the electrical phases).  

If you put me on the spot, I'd vote for 12V or 24V.  Depending on what cRIO hardware you're using, you could then get by with one power supply.

~Ben

[T_C]

Thanks again!!!!!