*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

 

[Jim Thompson]

On Tue, 5 Mar 2013 09:24:48 -0800 (PST), mrdarrett@gmail.com wrote:

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

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...

http://www.analog-innovations.com/SED/BoschMotor1.jpg

http://www.analog-innovations.com/SED/BoschMotor2.jpg

http://www.analog-innovations.com/SED/BoschMotor3.jpg

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

...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.

 

[ehsjr]

On 3/5/2013 12:24 PM, mrdarrett@gmail.com wrote:

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?

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

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

 

[Jim Thompson]

On Tue, 5 Mar 2013 10:21:14 -0800 (PST), mrdarrett@gmail.com wrote:

On Tuesday, March 5, 2013 10:01:44 AM UTC-8, Jim Thompson wrote:
On Tue, 5 Mar 2013 09:24:48 -0800 (PST), mrdarrett@gmail.com wrote:



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



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...



http://www.analog-innovations.com/SED/BoschMotor1.jpg



http://www.analog-innovations.com/SED/BoschMotor2.jpg



http://www.analog-innovations.com/SED/BoschMotor3.jpg



Three phase blower motor for Mercedes A/C system. All on one chip

except for the three big HexFET's.



...Jim Thompson

[snip]


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.

http://www.youtube.com/watch?v=CWx5ji_sFUw

"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
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.

 

[ehsjr]

On 3/5/2013 1:45 PM, mrdarrett@gmail.com wrote:

On Tuesday, March 5, 2013 10:36:50 AM UTC-8, ehsjr wrote:
On 3/5/2013 12:24 PM, mrdarrett@gmail.com wrote:

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?



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

is the experimentation.


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...?

I did a search and found this for ~ $10.00
http://www.ebay.com/itm/30A-Brushless-Motor-Speed-Controller-RC-ESC-Parts-Y-/150463926575

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

 

[Phil Hobbs]

On 03/05/2013 01:01 PM, Jim Thompson wrote:

On Tue, 5 Mar 2013 09:24:48 -0800 (PST), mrdarrett@gmail.com wrote:

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

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...

http://www.analog-innovations.com/SED/BoschMotor1.jpg

http://www.analog-innovations.com/SED/BoschMotor2.jpg

http://www.analog-innovations.com/SED/BoschMotor3.jpg

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

...Jim Thompson

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

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net

 

On Tuesday, March 5, 2013 10:01:44 AM UTC-8, Jim Thompson wrote:

On Tue, 5 Mar 2013 09:24:48 -0800 (PST), mrdarrett@gmail.com wrote:



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



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...



http://www.analog-innovations.com/SED/BoschMotor1.jpg



http://www.analog-innovations.com/SED/BoschMotor2.jpg



http://www.analog-innovations.com/SED/BoschMotor3.jpg



Three phase blower motor for Mercedes A/C system. All on one chip

except for the three big HexFET's.



...Jim Thompson

--

| James E.Thompson | mens |

| Analog Innovations | et |

| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |

| Phoenix, Arizona 85048 Skype: Contacts Only | |

| Voice480)460-2350 Fax: Available upon request | Brass Rat |

| E-mail Icon at http://www.analog-innovations.com | 1962 |



I love to cook with wine. Sometimes I even put it in the food.

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.

http://www.youtube.com/watch?v=CWx5ji_sFUw

 

On Tuesday, March 5, 2013 10:36:50 AM UTC-8, ehsjr wrote:

On 3/5/2013 12:24 PM, mrdarrett@gmail.com wrote:

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?



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

is the experimentation.

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...?

 

On Tuesday, March 5, 2013 10:53:50 AM UTC-8, ehsjr wrote:

....

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





I did a search and found this for ~ $10.00

http://www.ebay.com/itm/30A-Brushless-Motor-Speed-Controller-RC-ESC-Parts-Y-/150463926575

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...

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

Will do, that sounds like fun!

Michael

 

On Tuesday, March 5, 2013 10:53:50 AM UTC-8, ehsjr wrote:

....

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



Ed

Well, okay, still needs a microcontroller...
http://ww1.microchip.com/downloads/en/appnotes/00857a.pdf

 

[Tim Wescott]

On Tue, 05 Mar 2013 11:40:53 -0700, Jim Thompson wrote:

On Tue, 5 Mar 2013 10:21:14 -0800 (PST), mrdarrett@gmail.com wrote:

On Tuesday, March 5, 2013 10:01:44 AM UTC-8, Jim Thompson wrote:
On Tue, 5 Mar 2013 09:24:48 -0800 (PST), mrdarrett@gmail.com wrote:



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



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...



http://www.analog-innovations.com/SED/BoschMotor1.jpg



http://www.analog-innovations.com/SED/BoschMotor2.jpg



http://www.analog-innovations.com/SED/BoschMotor3.jpg



Three phase blower motor for Mercedes A/C system. All on one chip

except for the three big HexFET's.



...Jim Thompson

[snip]


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.

http://www.youtube.com/watch?v=CWx5ji_sFUw

"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.

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?

--
Tim Wescott
Control system and signal processing consulting
www.wescottdesign.com

 

[Tim Wescott]

On Tue, 05 Mar 2013 10:59:18 -0800, mrdarrett wrote:

On Tuesday, March 5, 2013 10:53:50 AM UTC-8, ehsjr wrote:

...

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



Ed


Well, okay, still needs a microcontroller...
http://ww1.microchip.com/downloads/en/appnotes/00857a.pdf

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.

--
Tim Wescott
Control system and signal processing consulting
www.wescottdesign.com

 

On Wednesday, March 6, 2013 8:36:22 AM UTC-8, Tim Wescott wrote:

....

(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).

Oh yeah, PC fans!

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

http://pcbheaven.com/wikipages/How_PC_Fans_Work/

Thanks!

Michael

 

[Tim Wescott]

On Wed, 06 Mar 2013 09:01:03 -0800, mrdarrett wrote:

On Wednesday, March 6, 2013 8:36:22 AM UTC-8, Tim Wescott wrote:

...

(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).


Oh yeah, PC fans!

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

http://pcbheaven.com/wikipages/How_PC_Fans_Work/

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.

--
My liberal friends think I'm a conservative kook.
My conservative friends think I'm a liberal kook.
Why am I not happy that they have found common ground?

Tim Wescott, Communications, Control, Circuits & Software
http://www.wescottdesign.com

 

[Jim Thompson]

On Wed, 06 Mar 2013 10:36:22 -0600, Tim Wescott
<tim@seemywebsite.please> wrote:

On Tue, 05 Mar 2013 11:40:53 -0700, Jim Thompson wrote:

On Tue, 5 Mar 2013 10:21:14 -0800 (PST), mrdarrett@gmail.com wrote:

On Tuesday, March 5, 2013 10:01:44 AM UTC-8, Jim Thompson wrote:
On Tue, 5 Mar 2013 09:24:48 -0800 (PST), mrdarrett@gmail.com wrote:



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



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...



http://www.analog-innovations.com/SED/BoschMotor1.jpg



http://www.analog-innovations.com/SED/BoschMotor2.jpg



http://www.analog-innovations.com/SED/BoschMotor3.jpg



Three phase blower motor for Mercedes A/C system. All on one chip

except for the three big HexFET's.



...Jim Thompson

[snip]


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.

http://www.youtube.com/watch?v=CWx5ji_sFUw

"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.

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?

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

...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.

 

[Jasen Betts]

On 2013-03-06, Tim Wescott <tim@seemywebsite.please> wrote:

(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).

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.

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?

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

--
⚂⚃ 100% natural

--- news://freenews.netfront.net/ - complaints: news@netfront.net ---

 

[Ian Field]

<mrdarrett@gmail.com> wrote in message
news:43364862-70a6-4568-8335-39d101570d82@googlegroups.com...

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?

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

 

[Ian Field]

"Tim Wescott" <tim@seemywebsite.please> wrote in message
news:k9KdncChBLob7arMnZ2dnUVZ_vadnZ2d@giganews.com...

On Tue, 05 Mar 2013 11:40:53 -0700, Jim Thompson wrote:

On Tue, 5 Mar 2013 10:21:14 -0800 (PST), mrdarrett@gmail.com wrote:

On Tuesday, March 5, 2013 10:01:44 AM UTC-8, Jim Thompson wrote:
On Tue, 5 Mar 2013 09:24:48 -0800 (PST), mrdarrett@gmail.com wrote:



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



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...



http://www.analog-innovations.com/SED/BoschMotor1.jpg



http://www.analog-innovations.com/SED/BoschMotor2.jpg



http://www.analog-innovations.com/SED/BoschMotor3.jpg



Three phase blower motor for Mercedes A/C system. All on one chip

except for the three big HexFET's.



...Jim Thompson

[snip]


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.

http://www.youtube.com/watch?v=CWx5ji_sFUw

"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.

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).

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.

 

[Ian Field]

"Tim Wescott" <tim@seemywebsite.com> wrote in message
news:CsKdnW7HnZZAOarMnZ2dnUVZ_qidnZ2d@giganews.com...

On Wed, 06 Mar 2013 09:01:03 -0800, mrdarrett wrote:

On Wednesday, March 6, 2013 8:36:22 AM UTC-8, Tim Wescott wrote:

...

(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).


Oh yeah, PC fans!

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

http://pcbheaven.com/wikipages/How_PC_Fans_Work/

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.

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.

 

[whit3rd]

On Tuesday, March 5, 2013 9:24:48 AM UTC-8, mrda...@gmail.com wrote:

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.

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).

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

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.