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*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
 
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 | |

| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |

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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.

 
E

ehsjr

Jan 1, 1970
0
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
 
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...?
 
E

ehsjr

Jan 1, 1970
0
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
 
On Tuesday, March 5, 2013 10:53:50 AM UTC-8, ehsjr wrote:

....


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 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
 
J

Jasen Betts

Jan 1, 1970
0
(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.
 
W

whit3rd

Jan 1, 1970
0
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.
 
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