PSN-L Email List Message

Subject: Re: Gas Generator recommendations
From: Karl Cunningham karlc@..........
Date: Tue, 08 May 2001 13:35:29 -0700

Cap --

In a computer, the majority of the power consumed is at 5 volts.  As an 
indication, a 200W AT power supply I have has the following output rating:

+12V  8A     -12V  0.5A
+5V   23A    -5V   0.5A

Dropping a 12-volt battery to 5 volts with a linear regulator feeding 10 
amps would dissipate 70 watts in the regulator alone -- more than what's 
required to power the entire computer.  A switching supply is necessary to 
gain any savings over an inverter.  And the 12-volt nominal battery voltage 
would probably have to be regulated before feeding it to the computer's 
12-volt line.  All in all, this is no small task unless you're in the power 
supply business.


At 11:24 AM 5/8/2001 -0400, you wrote:

>Hi Travis,
>I like your idea and plan on eventually building a similar backup system.
>What I would like to know is how can I go about eliminating the 12V DC/120V
>AC inverter in your system. Since the computer ultimately runs on DC power,
>how can I just run it from the 12V batteries? Then a charger with an
>automatic cutoff when the batteries are fully charged, could be connected
>permanently to the 12 V batteries so they are always kept fully charged. If
>the 120V AC mains go down as is happening in California, the computer would
>not know it happened because it is running off the batteries. They will of
>course run down eventually but that problem can be taken care of with a
>generator. I have an 800 Watt Honda 120V AC generator that also has a 12 V DC
>output that could be used to keep the batteries charged until the mains came
>back on. I hope somebody can tell me what to do inside my computer to convert
>it to run on 12V DC from the batteries.


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Larry Cochrane <cochrane@..............>