[rescue] DC Voltage distro
adh at an.bradford.ma.us
Wed Sep 22 14:53:36 CDT 2004
" From: patrick at mail.zill.net (Patrick Giagnocavo)
" On Wed, Sep 22, 2004 at 02:00:37PM -0400, Sandwich Maker wrote:
" > " From: patrick at mail.zill.net (Patrick Giagnocavo)
" > "
" > " Aside:
" > "
" > " The old telco batteries are 2V batts and thus you need at least 24 of
" > " them for 48VDC. Or just 6 for 12VDC.
" > nit: 2v is a -cell-. a -battery- of cells makes a 'battery'.
" Maybe internally it is composed of a series of 2V cells wired in such
" a way as to be a battery?
telco tend to be single cells, and they made some really big ones -
2000a iirc, something like 2' dia x 3' tall.
balancing a parallel stack isn't easy since cell voltage changes with
charge, electrolyte density, temp etc. in a series stack, all the
current goes through every cell.
10ka batt plants are not unknown. but that's paralleling entire 48v
stacks, probably through some sort of power monitor. 
anecdote: when i worked at attbl, a craft person told me of the time
he dropped a crescent wrench onto the bus bars of a big metro co while
working on the overhead track. it should've been clipped to a
lanyard, per safety regs...
the wrench melted in half. the 48v bus didn't even glitch.
he was lucky. he could've caused a -very-nasty- batt explosion, just
from the current surge.
he kept the melted handle end on his belt as a safety reminder for
many years after.
 batts were supposed to hold up for 4h. the genset to take over,
in a medium co, was a 3600hp diesel.
Andrew Hay the genius nature
internet rambler is to see what all have seen
adh at an.bradford.ma.us and think what none thought
More information about the rescue