Leaving a server on all day

[Charles Swiger]

On Jun 8, 2004, at 4:06 PM, Bill Moran wrote:
> Charles Swiger <cswiger at mac.com> wrote:
>>
>> No need to guess, use an amp-meter.  :-)
>
> What a crazy idea.
>
> I seem to remember plugging monitors into a UPS in an attempt to use 
> the cheesy
> "load meter" lights to tell which was drawing more juice, when that 
> didn't
> show us any difference, we tried watching the power meter outside ... 
> trying to
> guess which monitor made it spin faster ...

:-)  The "smart" versions of UPSes (as in, APC's SmartUPS line) will 
often have a serial connection which not only does the "deassert DTR 
when the battery is low" thingy, but will communicate other information 
about the state of the UPS.  That will include the power consumption of 
the load measured more accurately than 5 green LEDs would be able to 
show you.

A really serious UPS, such as a PowerWare 9330, may have ethernet and 
SNMP support and will do things like tell you the power factor of the 
load, typically about 0.9 for computer stuff.  But I admit, a 20kVA UPS 
is outside of what a normal home user would want.  And the batteries 
are freaking heavy... :-)

>> I have one machine with an AMD 1800+ (1.54 MHz T'bred-B), which runs 
>> at
>> perhaps 48 or 50 C if the system is idle.  If I run something like
>> SETI at Home for a day or so, the CPU will go up to around 56 or even 57 
>> C
>> as a result of the load.  The difference in thermal output due to load
>> is very obvious.
>
> But is thermal output a reliable indicator of power usage?  Logically, 
> it seems
> like it would be, but I'd hate to assume.

Conservation of energy is a law, so any assumptions being made are 
pretty safe.

When you pump 0.5 amps @ 120VAC into a 60 watt light-bulb, you end up 
getting about 54 watts of radiant heat and about 6 watts of visible 
light.  A computer's CPU eats about the same amount of power, and sends 
a watt or so back out in terms of data signals, but most of the energy 
used by the processor to actually process data gets emitted as heat.

-- 
-Chuck