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Re: Harddisk clicks -> System freezes/reboots

Ric Moore:
>>> Tim, back to ohm's law, wouldn't low voltage also make it run hot???

Tim [answering about Ohm's law]: 
>> No.  Voltage and current are inter-related.  If a power supply is losing
>> the ability to "supply," the current will go down.  Correspondingly, the
>> voltage will reduce at the same time (due to lack of supply).

> In switching mode supplies (which is all there is on PC's these days),
> the problem with low voltage is that the switching transistors tend to
> stay on longer.  At some point the cores can saturate, and in that case
> low voltage = high current.  It is one of the big drawbacks to switch
> mode supplies.

I was under the impression that Ric was asking about low voltage
affecting the hard drive rather than the power supply.

Specific to Ohm's law, voltage going low would mean the current would,
too.  But the other situation you refer to (reluctance, oscillator
circuit design, etc.) is something else (not to do with Ohm's law).
While current consumption may go up within the power supply circuitry,
it wouldn't be *supplying* more current to the rest of the computer, at
the same time as supplying less voltage.

Oscillator design were never my strong point, they were badly taught and
my interests were elsewhere (usually things *NOT* oscillating).  ;-)  I
don't recall doing much LC theory with them, it was usually RC.  As a
matter of fact, I've got to resolve just that point in some equipment,
here.  A video effects mixer that's oscillating somewhere that it
shouldn't, so the pedestal clamp is going nuts.

So regarding Ric's question, if he means the hard drive getting hotter
if the current went down.  Probably not.  But then if some of the
circuitry latches up (gets stuck) when not properly powered, maybe it
could get hot.  But I'd hazard a guess that you might have a component
burn out, at the most, on the drive, but the rest of the drive wouldn't
get hot.  Much of the heat generated by a drive is the air resistance
against the platters as they spin.  With the servo that shuttles the
head back and forth adding to it.

> How's that for a design challenge?

Agreed that there are some challenges involved, but it's only a power
supply.  Switch mode power supplies are an old design idea.  It
shouldn't be that hard to make a good one for someone who's fluent with
them (i.e. the manufacturers who make thousands of them, yearly).  How
many more years of computer systems do we need before we can get one
with a decent power supply?  ;-)  There's certainly less complexity in
them than in the rest of the computer system.

(Currently running FC4, in case that's important to the thread)

Don't send private replies to my address, the mailbox is ignored.
I read messages from the public lists.

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