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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