On 11-04-97 Roy J. Tellason wrote to Day Brown... 
DB> The UPS designs I've seen are kinda pricey.  It is a lot  
DB> cheaper to make the power supply part if the input voltage is  
DB> 48 v DC,  which is commonly used as battery backup in Telco and  
DB> other types of critical commercial/business applications.  
 RJ> Hmm. 
It even cheaper for them, because there is a lot of well tested 
designs and components for 48VDC input inverters made for Telco 
and military applications.  A 12VDC input power supply would mean 
that they would haveta do more engineering. ;-} 
 
DB> And, then by locking in the user to some higher voltage, they  
DB> try  to lock him into using their *proprietary* batteries... in  
DB> case you want more backup time in a small, or home office.  
 RJ>  
 RJ> I can see a somewhat higher voltage,  it being easier to design stuff 
 RJ> that will handle a fair amount of power without getting into  
 RJ> absurd current levels.  It can get kinda hard to solder  
 RJ> battery cable sized wire to some of those transistor  
 RJ> terminals,  too...     
You bet.  Part of my solution is to design the whole desktop to 
run on 12v input power; more specifically, select components that 
are more efficient with such power as the battery can provide,
without having to use 4 or 8 gauge wire.  Typically, I get systems 
to run on less than 5 amps, and ordinary 12 AWG wire is plenty ;-) 
 RJ> Some of the forklift batteries I've seen are 48 volts.   
 RJ> I'll bet they'd run a computer for a *LONG* time! 
Probly.  I have used pairs of 6v golf cart cells to keep the PC 
cranking for 24-30 hours. 
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