[CentOS] Power-outage

John R Pierce pierce at hogranch.com
Mon Jul 4 17:57:43 UTC 2011

On 07/01/11 4:05 AM, Timothy Murphy wrote:
> It seems to me that it should be possible
> to have a simple, torch-battery operated

assuming 'torch' in this context means what us yank's call a flashlight, 
and that a 'torch battery' is a C or D cell, lets see how much juice we 
could get out of a reasonable setup..

According to HP's 'quick specs', the Microserver has a 150W supply, that 
nominally draws 0.63 A (from 115VAC) or 0.35 A rom 220VAC, about 75 watts.

According to wikipedia, an alkaline D cell is typically rated at 1.2 amp 
hours at 1.5 volts.   Most inexpensive AC inverters run on 12V 
(automobile power), so we'd need 8 of them to get 1.2AH at 12V or about 
14 watt*hours...   My calculations seem to suggest you'd get maybe 9 
minutes total from those 8 batteries with an 80% efficient AC inverter 
at 75 watts.   And then of course, you'd be throwing those 8 D cells 
away and replacing them with new ones.

NiCAD or NiMH rechargeable batteries aren't particularly suitable for 
this application, you'd need 10 of them as they are 1.2V, and they don't 
do well as standby power since they self discharge when idle for long 
periods.   UPS's almost always use lead-acid batteries as they are far 
more suitable for standby power applications.

A UPS is little more than a rechargeable battery, an A/C inverter 
circuit, a battery charger, and a controller for all that which also 
signals your computer when the power is failing.

john r pierce                            N 37, W 122
santa cruz ca                         mid-left coast

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