Day Brown wrote in a message to Roy J. Tellason:
 DB>  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. 
 DB> It even cheaper for them, because there is a lot of well tested 
 DB>  designs and components for 48VDC input inverters made for 
 DB> Telco  and military applications.  A 12VDC input power supply 
 DB> would mean  that they would haveta do more engineering. ;-} 
Double the voltage and halve the current.  Since the phone systems use 48v,  
they can operate a relay or two based on something that's happening *miles* 
away.  And use some pretty small wire to do what they do,  too.
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> I can see a somewhat higher voltage,  it being easier to design 
 RJ> stuff that will handle a fair amount of power without getting 
 RJ> into absurd current levels.  It can get kinda hard to solder 
 RJ> battery cable sized wire to some of those transistor terminals, 
 RJ> too...     
 DB> You bet.  Part of my solution is to design the whole desktop to 
 DB> run on 12v input power; more specifically, select components 
 DB> that are more efficient with such power as the battery can 
 DB> provide, without having to use 4 or 8 gauge wire.  Typically, I 
 DB> get systems to run on less than 5 amps, and ordinary 12 AWG 
 DB> wire is plenty ;-)
I guess it all depends on what level of power you need and how far it's gotta 
go...
 RJ> Some of the forklift batteries I've seen are 48 volts. I'll 
 RJ> bet they'd run a computer for a *LONG* time!
 DB> Probly.  I have used pairs of 6v golf cart cells to keep the PC 
 DB> cranking for 24-30 hours.
That's all?  I would have thought they'd run one longer than that.  Still,  
you can get several different amp-hour ratings in the same size case...
And then a step up from that is the so-called "floor sweeper" battery,  also 
typically a six volt unit,  and similar in sizing and style to the golf cart 
battery,  but *bigger*.  Usually by a significant amount...
email: roy.j.tellason%tanstaaf@frackit.com 
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