*analog* brushless DC motor control?

My son and I took apart a dead hard drive, and salvaged the motor. Apparently it's a brushless DC motor that needs a dedicated controller.

Any way it can be powered by analog, discrete circuitry?

If I understand it correctly, each of the three power wires needs to be energized while the other two wires are held at ground, and the three wires take turns being powered by, what, +5V, right?

Thanks,

Michael

Reply to
mrdarrett
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it's a brushless DC motor that needs a dedicated controller.

energized while the other two wires are held at ground, and the three wires take turns being powered by, what, +5V, right?

Are there only three leads total, or is there a fourth, or a path to case? Or maybe it's two-phase instead of three?

Or it could be self-commutated, with the third lead as a speed sensing output.

Hard to say. Can you trace back thru the board it was on?

Here's my big mama...

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Three phase blower motor for Mercedes A/C system. All on one chip except for the three big HexFET's. ...Jim Thompson

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| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
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Reply to
Jim Thompson

Apparently it's a brushless DC motor that needs a dedicated controller.

energized while the other two wires are held at ground, and the three wires take turns being powered by, what, +5V, right?

Oh, nice! Still have a controller chip in there though, huh.

Wiring... I'm not sure; I'll have to check it more thoroughly when I get home. There were three very obvious wires, but from some YouTube vids I saw there is sometimes a fourth wire...

I did see a very clever way to turn the hard disk platter itself into a commutator, using electrical tape, and turn the whole motor into a brushed DC motor, but that kind of defeats the purpose of a brushless DC motor.

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Reply to
mrdarrett

it's a brushless DC motor that needs a dedicated controller.

Yes, but it's not worth the effort, unless the goal is the experimentation.

There's a relatively cheap (< $20) controller available on Ebay that will work well to control the motor. I'd post the details if I could remember, but ... Grumble.

Ed

energized while the other two wires are held at ground, and the three wires take turns being powered by, what, +5V, right?

Reply to
ehsjr

Apparently it's a brushless DC motor that needs a dedicated controller.

energized while the other two wires are held at ground, and the three wires take turns being powered by, what, +5V, right?

[snip]

There were three very obvious wires, but from some YouTube vids I saw there is sometimes a fourth wire...

commutator, using electrical tape, and turn the whole motor into a brushed DC motor, but that kind of defeats the purpose of a brushless DC motor.

"Big mama" was EC (electronically commutated). The back EMF provides the location. The "starter" was a "ring-around-the-rosy" shift-register "oscillator", which then got synchronized via the back EMF. ...Jim Thompson

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| James E.Thompson                                 |    mens     | 
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Reply to
Jim Thompson

Apparently it's a brushless DC motor that needs a dedicated controller.

Right, that's the goal. =) I know there are cheap R/C motor controllers that control 3-phase DC motors, but... yeah.

Seems like some sort of modified Astable Multivibrator should do the trick...?

Reply to
mrdarrett

Apparently it's a brushless DC motor that needs a dedicated controller.

control 3-phase DC motors, but... yeah.

I did a search and found this for ~ $10.00

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Regarding the experiment - I did that a while back and found that it was touchy as all get out, very critical adjustment of the speed control pot to get it to run. As I recall, I _very_ rarely could get it to self start - I had to manually spin it to start it, and even that was difficult.

Read up on brush-less motor control, it's interesting. :-)

Ed

Reply to
ehsjr

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trick...?

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Good price! Then again, I just took apart a 9-amp, 110v electric weed eater that could never hold the weed-eating spool properly, on a hunch put it on 24 VDC, and it WORKED! That is going to be fun.

And of course I horrified my 10-year-old son by plugging in a C-frame fan motor directly into the outlet... wires only, no plug... ahahaha...

Will do, that sounds like fun!

Michael

Reply to
mrdarrett

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Well, okay, still needs a microcontroller...

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Reply to
mrdarrett

Apparently it's a brushless DC motor that needs a dedicated controller.

energized while the other two wires are held at ground, and the three wires take turns being powered by, what, +5V, right?

IIRC HDD motors are all BLDC with back-EMF sensing. Hall sensing is great if you need good control at low speed, but HDD motors run at only one speed.

Cheers

Phil Hobbs

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Reply to
Phil Hobbs

AFAIK that's the general method for electronically commutated brushless motors: you look at back EMF, and you have some other way to start it. That applies whether you do it digitally or analogly.

(Except for the cheap computer fans, which manage to have a circuit which self-oscillates on startup, yet synchronize to the motor on run. It's something like three transistors -- I remember being astonished at the simplicity, 25 years ago when I took a few apart. Now it's probably done with one chip).

Jim doesn't say, but if the motor is a true brushless DC motor (i.e., if it has trapezoidal back EMF) then in general the wires are driven by half bridges, with one of them left open at any one time. That open wire is monitored for voltage, which is where you get your back EMF.

I'm not sure what Jim (and the motor people) did that let him get away with just three FETs -- a Y configuration with the fourth wire connected to +V?

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Tim Wescott 
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Tim Wescott

You can do sensorless brushless motor control with all discrete circuits. In the implementation that I am (vaguely) familiar with you'll need some logic chips in there (the commutation events that you can pick out happen in the center of the hang time between the switching events that you need to generate -- so you need a PLL and a state machine, not to mention the self-start circuit).

If you have an oscilloscope, start by spinning the motor and looking at the voltage between pairs of wires.

Then see if you can hook the motor up and make it work as a 3-phase stepper. If you can, you've just put your feet on the path to the self- start circuit.

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Tim Wescott 
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Reply to
Tim Wescott

...

Oh yeah, PC fans!

Researching them now... found this after a brief search.

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Thanks!

Michael

Reply to
mrdarrett

Hmm. My memory was incorrect, or the fans I had were different. If there's a hall sensor in there, then the fan is not sensorless -- which means that you have a different animal than your disk drive motor.

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Reply to
Tim Wescott

Yes. Three FET's switched sequentially to ground... mid-point of the "Y" connected to +V. ...Jim Thompson

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| James E.Thompson                                 |    mens     | 
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Reply to
Jim Thompson

last time I pulled one apart it had a single coil with shaded poles and a hall-effect chip to detect the rotor position,

the ones used on CPUs seem to be more complex, the go in to a different mode when forcibly stopped and then short time later start up.

Y 4-wire Y-connected motors seem fairly common on hard drives.

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Reply to
Jasen Betts

At least 1 of the hobby magazines has published articles on recycling HDD spindle motors, might have been Elektor or possibly EPE.

Reply to
Ian Field

AFAICR all the PC fans I've taken apart had hall effect sensors, the later ones had the hall sensor integrated into the drive chip.

Reply to
Ian Field

I think drives like the old Seagate 5 1/4 low profile ones had hall sensors, although more recently, as someone else commented, I think they use back EMF sensing.

Reply to
Ian Field

it's a brushless DC motor that needs a dedicated controller.

As others have said, it's a four-wire Y (wye) wired motor; this makes it a synchronous (permanent magnet) AC motor. It's certainly brushless (but for an AC motor, that's not noteworthy).

The easiest way to generate three out-of-phase drive signals is with some kind of digital logic, but you can make an analog phase-shift oscillator with taps to get all three phases.

Simple speed control can be had by controlling a VCO (CD4046 works well) that drives a three-flipflop twisted tail counter (to generate three phases) which drives three transistors (I'd use discrete NPNs, but MOS and monolithic transistor arrays are also good). Attach the center of the wye to +12V through a suitable limit resistor, and each branch to a switch-to-ground transistor.

Because this IS an AC motor, you can get better efficiency by driving the windings with AC (without the DC bias). Modulating the DC produces a mix of DC and AC currents, and only the AC part of the drive is actually torque-producing.

Reply to
whit3rd

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