I have one of these cheap BLDC controllers that is giving me trouble.



I have it attached to a hard drive. Seemed to work fine for a while but it is no longer working. I want to try a different hard drive. Or create my own BLDC controller. Either way first step is to determine the winding.

My motor has 4 wires. First thought was to measure the resistance between the terminals. I tried that and what is odd is the resistance seems to change as I leave the meter on the connections. The average is ~ 2 ohms but it can change as much as .5 ohms.

So how do I determine the windings?

P.S. Part of that changing seems to be coming from my meter.

 

Never personally took one a part, but by all evidence out there they are either a star or delta connected outrunner motor, 3 wire or 4 wire.
As long as the rotor is stationary I would think it should be possible to get a steady reading.
Max.

 

Measuring coils and other low-resistance stuff with a multimeter is always frustrating, anything under 10 ohms becomes fraught with uncertainties from contact and lead resistance.

What is do is set my bench supply to constant current mode, 1 amp, then hook it to the coil.
Carefully, with my DVM on DC volts, I measure the voltage drop ON THE DEVICE TERMINALS DIRECTLY to avoid any contact or wiring resistance. The meter reads the resistance directly, 1 ohm-per-volt. Just make sure your coil can handle 1 amp without melting.

Its the poor man's 4 terminal ohm meter.

 

Or create my own BLDC controller.

Tons of ways to do it on Google, take your pick - https://www.google.com/search?client=firefox-b-1-ab&q=hard+drive+motor+control

 

Tons of ways to do it on Google, take your pick - https://www.google.com/search?client=firefox-b-1-ab&q=hard+drive+motor+control

Don't you think I know that? I have found those articles. Lots of articles on how to run the drive (I already know that). But I have yet to find an article that tells you how to figure out the wiring. If I found one I would not be posting here.

 

What is do is set my bench supply to constant current mode, 1 amp, then hook it to the coil.

Seems a bit too much for the tiny harddrive motor. Soemthing like 100mA would be more reasonable.

 

Measuring coils and other low-resistance stuff with a multimeter is always frustrating, anything under 10 ohms becomes fraught with uncertainties from contact and lead resistance.

What is do is set my bench supply to constant current mode, 1 amp, then hook it to the coil.
Carefully, with my DVM on DC volts, I measure the voltage drop ON THE DEVICE TERMINALS DIRECTLY to avoid any contact or wiring resistance. The meter reads the resistance directly, 1 ohm-per-volt. Just make sure your coil can handle 1 amp without melting.

Its the poor man's 4 terminal ohm meter.

Duh I should have thought about this. You do similar when determining the resistance of an unknown meter movement.


So how do I know if the coil can handle one amp? Would 10 ma do then just multiply? Really I don't need to know the resistance right now. Just need to know the differences.

 

If you can measure a reasonable drop at 10mA, then just use that.

 

Don't you think I know that? I have found those articles. Lots of articles on how to run the drive (I already know that). But I have yet to find an article that tells you how to figure out the wiring. If I found one I would not be posting here.

To quote Steve Martin, "well, excuse meeee". Then why not look for this - https://www.google.com/search?client=firefox-b-1-ab&q=hard+drive+motor+wiring+schematic

 

I just measured an old one I had with my Fluke meter and exactly measures 2.0Ω from star point to each of the three windings.
Typically just has any other 3phase or BLDC motor has.
Max.

 

I just measured an old one I had with my Fluke meter and exactly measures 2.0Ω from star point to each of the three windings.
Typically just has any other 3phase or BLDC motor has.
Max.

How many wires do you have?

 

Four.
Appears to be 3 star connected winding's.
Max.

 

Four.
Appears to be 3 star connected winding's.
Max.

OK now find the common. How do you do that if they are all 2 ohms? 4 wires would not one of them be common?

 

2.0 ohm from the star connection (common) to each winding (phase).
Phase to phase is 4.0 ohms.
Also if you spin it, it generates AC, as read on the meter.
Max.

 

BTW, if you identify the star point, you should see this on a 'scope when spun.
(Not the Commutation tracks however).
Max.

 

BTW, if you identify the star point, you should see this on a 'scope when spun.
(Not the Commutation tracks however).
Max.

OK you are going to have to speak laymen.

What is the 'star point" ? Is that the common?

What are the "Commutation tracks" is that the other connections?

What do you mean by spin? With your hands or by applying a voltage?

 

Here is the basic star connected motor.
The N as seen would be the Star common to each winding.


For this motor, disregard the commutation tracks in the PDF, just the three generated sine waves can be seen if connecting a scope, common to N or star and the 'scope channel lead to A,B or C.
Spin the motor by hand and you should see the sine generated sine wave.
I also see the voltage on a meter on the AC range.
Max.

 

So I tried that. I indeed get the sine wave but I get it on any two pins. Am I missing something?

 

you need at least two channels, beacuse the relative amplitude will tell you what is the center and what are the points of the star.

 

you need at least two channels, beacuse the relative amplitude will tell you what is the center and what are the points of the star.

REALLY hard to see that way but looks like there is a difference. But I checked with the ohm meter again. Now it works. I do see a difference of about twice when going between two coil pins as oppose from a coil pin to common. Not sure what the issue was before.