[Dclug] UPS hacking; was DSL

[David C Niemi]

It is a good thought to power the device directly from batteries, and 
you're right, it would be a lot more efficient.  However, the battery 
voltage will vary so you may need a DC-DC converter or at least a linear 
regulator to turn the varying battery voltage into a steady one like the 
DSL modem will expect.

Nicads (or NiMH) are not a good choice for UPS type applications because 
they do not take well to being kept charged all the time.  For stationary 
applications like this plain old lead acid is a lot cheaper and will 
probably last longer on a "float" charge.  FYI Nicads and NiMH produce 
only about 1.2-1.3V per cell depending on state of charge.  For portable 
applications, lithium ion or lithium ion polymer is preferable, but you 
must design the circuit so they can never be overcharged or 
overdischarged.

DCN

On Mon, 7 Jan 2008, Ed James wrote:
> I wonder if perhaps a box of NiCads (or whatever) might be better?
> Seems strange to take house current to keep high-voltage batteries
> charged, and then convert their power into AC, just to convert it
> back to DC for various DC devices via the usual wallwarts.
>
> For example, 7 1.5 volt cells in series would supply 10.5 volts to run
> a 10.5 volt DSL modem. I'm thinking wallwart, thru a diode, to the
> NiCads, then NiCads to the Modem.
>
> I've seen setups where a car battery feeds a circuit board which in
> turn produces the different voltages needed by some mobos, so that
> the clunky power supply isn't even needed.
>
> Ed James

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| David C Niemi  (Reston, VA, USA)  niemi at tuxers dot net |
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