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Re: [Amps] -48 Volt Switching Power Supplies

To: amps@contesting.com
Subject: Re: [Amps] -48 Volt Switching Power Supplies
From: Ian White GM3SEK <gm3sek@ifwtech.co.uk>
Reply-to: Ian White GM3SEK <gm3sek@ifwtech.co.uk>
Date: Tue, 22 Nov 2005 07:59:00 +0000
List-post: <mailto:amps@contesting.com>
HAROLD B MANDEL wrote:
>Before running off and making a cash offer on a surplus -48 Volt 
>switcher supply from a telecom location please consider that it may or 
>may not be working.  It takes an Act of Congress to get these replaced, 
>and the one thing that qualifies for replacement is when the magic has 
>gone out when the white smoke came out the top.
>
But in other jurisdictions they can be bought for peanuts, with the 
magic smoke still inside. Part of the reason for the low price is that 
they often don't seem to be working... but see below.


>Additionally, many of these units operate from 240 volts a.c., 
>single-phase, of course

Oh good!  :-)

>
>Additionally, many of these units connect to a controller in the power 
>plant that controls the output voltage and without a controller will 
>not emit.
>
>Additionally, several models need to be connected to a string of 
>battery cells before turning on any D.C. output. This is called the 
>Reference Voltage and when a string of rectifiers are operated in 
>parallel the common  battery plant enables the central and rectifier 
>controllers to adjust the float voltage to a few hundredths of a volt 
>regulation.
>
That's right. If the PSU is a plug-in module, it almost certainly won't 
start if you simply apply mains. You'll probably need to hotwire the 
control connector to make it think it's plugged into a rack.

The answer could be as simple as shorting two pins on the control 
connector (one of which is likely to be the control ground bus). If it 
also needs a reference voltage input, it's like having an extra lock... 
you may never get in without a manual.


-- 
73 from Ian GM3SEK
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