For pickup: VAX-11/750 and RK07

Patrick Finnegan pat at
Sat Jun 6 14:59:43 CDT 2009

On Saturday 06 June 2009, Chuck Guzis wrote:
> The charging circuit is pretty crude by modern standards--an LM317K
> TO3 regulator on a large (4"x6") heatsink with a 50W zener and a
> thermostatic switch.  It could probably benefit with some upgrading
> to a "smarter" circuit.
> This UPS has been in continuous service since 1989.

There's really only 3 reasons I bother upgrading my UPSes whenever I can 
find a newer, cheap to free one:

1) Newer models seem to have a charging circuit that's smart enough not 
to overcharge nearly-dead batteries to the point at which they expand 
and blow their seals.  Cleaning batteries that have done this out of a 
UPS runs somewhere from "difficult" to "a complete mess".  And, I've 
had to clean this up several times out of UPSes I've received; the only 
good thing is that it usually makes the UPS much less expensive to 
acquire. :)

2) Higher-efficiency inverters mean more runtime out of the same 
batteries, and usually at the same time, a lighter UPS.  Considering 
how often I seem to move stuff around, lighter is definately a plus.

3) Better monitoring.  I really like the amount of information that I 
can get out of SNMP on a modern UPS's network card.

That said, if you replace the batteries as recommended (3-5 years) with 
good quality batteries, an older UPS will do quite admirably for most 
people, and can be more useful for hacking up to do different things 
(like mashing three of them into being a 3-phase inverter, which is 
somewhere on my project list, to power stuff like my IBM 3420, and 
Liebert System/3).

Purdue University Research Computing ---
The Computer Refuge                  ---

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