Computer power supplies and motors

[nfmisso]

CD, DVD and hard drive motors - information from an ex-hard drive designer.

CD drives, DVD drives and some early PC hard drives use stepper motors to position the head(s). Stepper motors respond to a digital pulse train, moving one step for each pulse, most are multi-phase motors, meaning that they have more than one set of windings that need to be energized in a particular order to go one direction, and a different order to go the other. It is practical the trace the board electronic on early drives and determine where to break in to provide your own commands. Newer ones are more intergrated, and this is not practical.

The spindle motors are three phase brushless DC motors. They operate on varying voltage like standard DC motors, and in addition, the current must be switched between the appropriate phases as the motor position changes. Older drives have hall sensors on the motor to determine position, the newer ones use a bemf detection scheme to determine when to switch phases. Applying straight DC to a brushless DC motor will cause it to oscillate back and forth, like applying AC to a DC motor does. They can be driven open loop by three phase variable frequency AC. They are designed to spin in one direction only. The newer fluid bearing hard disk drive spindle motors will pump out all of thier lubricant if spun in the wrong direction.

[rrinker]

You won't be able to do anything with a stepper motor without a drive circuit. They need to be 'pulsed' to step. The head motor in a floppy drive works the same way, the gearing is such that the head moves the proper distance with each step, there is no feedback that tells the drive that the head is over a certain track. This is why floppy drives can get out of alignment, 5 steps SHOULD be track 5 but it's really ending up around track 4.5, so it won't read the disks, and any disks formatted and written in the bad drive don't work in another one. I don't think a stepper motor can handle constantly applied voltage, in general.
Now the tray open/close motor, the gearsm and the rack associated with that sure make useful parts. The spindle motor is probably also a stepper, although it might just be a regular motor with a tachometer output, as CD rotational speed needs to vary as the head moves in and out.

[Anonymous]

Thanks for the information. My biggest problem so far has been that I keep getting distracted in the planning but so far am having a lot of fun. Some computer technicians and I took apart an old 5X CD drive yesterday and looked at the parts. There are 3 small motors, several reduction gears and a well made slide rack (it holds the laser. The computer guys said that one of the moters was a "step motor" and apparently goes to a particular position based on the voltage it receives. I'm not sure what this is good for but I think it will be interesting to experiment with.

PS: I too have access to more old computer stuff than I could ever use.

[rrinker]

In model railroad terms, yeah, they sure do generate a lot of power. I wondered why I always saved the power supply when I got rid of an old ocmputer - well, I have a closet full of workign computer power supplies that are useless in a modern computer. But think of this - a Tortoise draws ~15ma when stalled. A 15 amp power supply will run 1000 of them! Even with 2 decks, my home layout will NEVER have 1000 turnouts!
Now to order up some big power resistors...

The only thing I'm disappointed with is that 12v isn't enough to feed a DCC booster - a computer power supply would be PERFECT otherwise.

[jwmurrayjr]

The ATX power supply makes a dandy PS for the layout. Here's one that I converted for mine. I got a lot of good info from the Murray State link that rrinker posted. Especially about mounting the load resistor. Andy has a very nice solution. The resistor stays cool.

Here's my PS with taps for 3.5vac, 5 vac and 12 vac.



Here's a little blurb on how I did the conversion in an MRR context.. A link to Andy's site is also included on my site.

http://www.trainweb.org/silversanjuan/Page3/Page16.html

If you don't have an old PS to convert they are available on eBay and other places for very little (Sometimes $5 or so). They produce a lot of power.

[cacole]

I have used three different types of computer power supplies successfully for lights, crossing signals, sound modules, and to power DCC boosters. If your power suppy has a schematic of the motherboard's 20 pin connector, there are two connections that can have a jumper placed across them to bypass the load sensor, because this jumper gives the power supply the same reading it would get if it was connected to a motherboard and had a load on it. All you have to do is connect the sensor lead to ground. I have never tried using a motor out of a disc drive, but some possible uses for these would be animation.

[cwclark]

they are going to have to have a significant load on them all the time..in other words, they won't work unless you have enough equipment drawing a current from them so that they won't shut down due to low load...I'm using one for a 5v power source to operate my train detection circuits...I have built the circuits already but I haven't hooked it up yet because i haven't built enough of the searchlight targets yet....in theory they should work...go to www.gatewaynmra.org There is an explanation for the computer power sources there under "electronic projects" that will explain why you have to have such a big load on them to work Chuck[:D]

[rrinker]

Yes, you can do this, but a computer power supply is a switchign power supply and generally will not work without a load on it. Here is a web site that shows you how to modify the power supply to work for powering lights or whatever you want to power.

http://web2.murraystate.edu/andy.batts/ps/powersupply.htm

Having it connected to 100 GoW bulbs does not constitute a load, you need a resistor as in the example.

[Anonymous]

I'm pondering setting up an HO layout and am intrigued by the idea of using power supplies from old computers and motors, gears, tails, etc from old disk and CD drives. These parts seem to be of high quality and are available free from tons of old computers.

Does anyone have any experience with this?