mailing list archives
Re: Black box that allows just an A or B DC feed
From: "Barton F Bruce" <barton () gnaps com>
Date: Mon, 9 Jun 2003 14:28:24 -0400
You just need two suitably large diodes. Big ones need heatsinks.
You will find some of the rack-top fuse panel makers that include diode "OR-ing" their main A and B feeds. No
switchover time at
all. The power is just there.
Pretty sure Telect has some. Beware of Hendry. Good stuff, but savagely overpriced unless you are buying Bell class
quantities and a
huge percent of neat options in the catalog seem to never have been built! They offer every weird combo anyone might
want, and then
build when they see the order. You WILL wait if it isn't a popular item on some distributor's shelf.
The Canadian NoranTel folks are VERY responsive and make a nice 1U 200 AMPS per A/B feed panel that has up to 50 amps
for each of 4
A/B outputs as well as a pile of grasshopper outputs for smaller up to 15 AMP loads. The unit we get does not have
diodes, but if
they don't have something suitable, these folks are very responsive to new products fast.
There may even be some fuse panel vendor with those diodes on the individual outputs., but I don't remember any.
Even worse than that single input device is the sleazy device that LOOKS as though it has dual inputs but is actually
with the 2 connections bussed together with no blocking diodes (and no woarnin to customers...) and when wired as 2
will gleefully backfeed A to B or B to A depending on what died. This is no problem if a fuse/breaker to just this
device dies, but
when a main A or B feed dies (either to the rack or worse to a BDFB/CDBD) everything else on that panel is now being
the clueless device.
Cisco's CERENT 15454 SONET ADMs will try this for you and the result is typically just losing the 15454 needlessly when
a main fuse
feeding it blows because its own fuses can't carry the rest of the rack/room/<whatever> that it is trying to backfeed
and the wrong
one of those 2 fuses to the 15454 may well go first. And a SONET ADM is not what you want to have die - especially
We have been seriously considering making a small diode-or device just for the darn 15454s. Main fuses don't go often,
have been known to intentionally kill an A or a B feed for safety during maintenance when they are "sure" everything is
Just warn them about 15454s so they can kill the correct backfeed path first.
NB that the fuse panel with diode OR-ed main inputs does fix the backfeed liability, but does not give you the backup
individual device fuses for the single input device.
----- Original Message -----
From: "james" <hackerwacker () tarpit cybermesa com>
To: <nanog () nanog org>
Sent: Monday, June 09, 2003 1:38 PM
Subject: Black box that allows just an A or B DC feed
*This message was transferred with a trial version of CommuniGate(tm) Pro*
I have a device that only has one DC power input. Is there a box that
can accept an A & B DC leg, keep both isolated, & and feed my
device with just A or B ? ie, if the A or B leg fails at the co-lo
this blackbox will switch to what ever leg is up. Quickly, I hope !
Or are there other ways to solve this issue ?
Routing and Security Administrator
jamesh () cybermesa com
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