How to recover a crashed laptop hard disk (windows NTFS)

Erica Eshoo wrote:

It is science but the advice is abstracted from many electrical engineering disciplines, and couched in laypersons terms. First - DC motor theory: the motor in the drive that spins the disk has whats called 'inrush current'. High inrush occurs because at startup, the motor does not generated enough back EMF to equal the nameplate voltage rating of the motor, and for a few tenths of a second, it (the motor windings) looks close to a short circuit to the power supply. Technically, at the location of a short circuit, the current will go to infinity (or as much as the power supply can deliver) and the voltage will go to zero. The current in the motor windings or fields cutting through a magnetic field is what produces the torque that causes the rotor to spin. Power supply theory: Now, if the power supply that is powering the motor is relatively small (e.g. low wattage), in the startup phase of the motor when the 'short circuit' is present, the power supply may not be capable of supplying the current that is needed by the motor so that it can develop the necessary torque to start rotation. The torque that is developed must overcome the friction caused by the bearings, etc and move the mass on the shaft (armature plus disk)in the motor. Power supplies may have additional circuit protection devices that limit the current, as well as under and over voltage protection. These as well will limit the power (current x voltage) that the power supply can output, thus not allowing the motor to produce the necessary torque to produce rotation.

The implication that a power supply 'pushes' power into a device is incorrect, and a laymans attempt at explaining electrical circuit theory. IMHO, it is quite a 'reach' to suggest that getting a larger wattage power supply can fix the problem, although it can work. The same effect could be obtained by taking some of the load OFF of the smaller supply (e.g. disconnect bus loads, DVD/CDs/floppies, etc, or even pull memory out of the MB (leave all but minimum).

John

Reply to
John Hudak
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Does not aplay, since these motors are not connected to power directly, but through a sphisticated motro controller circuit, that, among other things, limits startup current.

Again, does not apply for a PC PSU, unless it is very close to failing. A HDD draws up to 30W on startup, that should overload no PC PSU.

What is completely missing is that if the PSU is this weak, it is close to death in the first place.

Arno

Reply to
Arno Wagner

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