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Subject: Re: Power options
From: Laurent Giroud (laurent.giroud_at_libertysurf.fr)
Date: 2004-04-18


> > Physically speaking, it doesn't matter how fast or slow you
> > speed up the disk. It takes the same energy. Faster spinup
> > means higher power for a shorter time.
> > The energy depends on the disk RPM (this is why 4200 RPM
>
> It would be even worse to have a slower spinup. As Jörg
> explained, the amount of energy needed to accelerate the disk
> platters itself does not depend on how fast it is done. But in
> real-world physics there is always friction, and if you would
> have a slower spinup the disk would spin longer, rising the
> enrgy loss generated by friction.

Are you sure that this would lead to a greater (mecanical) energy consumption ?
I seem to recall that friction is function of speed, so a lower speed would lead to a lower friction. But I might be wrong, there, as my last physics courses are far behind me :)

I think Jörg is indeed right when he says that the amount of mecanical energy required to spinup the disk will be the same whatever the acceleration, since it's integrated over the time required to reach full speed.

However, (beware, this is nit-picking) the drain on the batteries might vary depending on the acceleration.
-> do batteries better react to a high power drain over a short time or a lower one over a bigger time ?

Even if the total amount of electrical energy delivered to the disk until full speed would be the same, the drain on the batteries might be different depending on whether they are more efficient in delivering rapid bursts or constant small flows of current.
But then, we are not sure at all that there's a way to have a slower spinup so this is certainly not a big issue to discuss ;)

Regards,
Laurent
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