On Sun, 29 Jul 2018 18:03:09 +0000, Bob Eager wrote:

On Fri, 27 Jul 2018 23:29:39 +0000, Johnny B Good wrote:

The more recent (less than 20 years old) APC SmartUPS series can be
configured via their serial/USB interface to float charge at less than
the default[1] 2.3v per cell setting, allowing you to chose a less
corrosive 2.25v per cell (13.5v per 12v SLA) setting. I'm not sure, but
I think even that ancient SmartUPS2000 of mine originally had such
provision (I could look at but I could not touch any of the settings
for some undetermined reason).

I know this has been discussed before, but can you please give a link to
a resource for doing this (for those A{C units that support it)?

I have three APC units here, and I'd be interested in doing it. My
batteries last 3-4 years depending on the unit.

I see Andy has already provided a link to a useful website. Bear in mind
that the Back-UPS series generally didn't cater at all for such external
monitoring and control. The Back-UPS Pro and the Smart-UPS models are
equipped with the proprietary wired DB9 serial port (later models used a
USB interface) required to support remote monitoring and control.

APC provide software called PowerChute. I see I have a copy of
PowerChutePersonalEdition which I downloaded (presumably for free after
registering on line) from APC's support site way back in Nov 2008. I've
also got a copy of winapcupsd-3.14.4.exe I downloaded a few days later
which is an open source APC power monitoring daemon for windows (I note
that the latest version is now at 3.14.14).

You can google for details on how to wire up the UPS end of a basic 3
wire serial interface cable once you're ready to try the remote access
feature of a suitably equipped APC UPS.

Having browsed through most of the many circuit diagrams for APC's
earlier UPSes (circa 1995 to 2004 that I'd downloaded from a Russian
website back in 2008) to track down the diagrams for that tiny BackUPS500
I mentioned earlier to verify the battery charging circuit that I'd had
to repair just 12 months or so after purchasing it from a radioham rally
trader (unused and in its original packaging for just 25 quid). I see
that the analogue regulator IC that I'd had to replace must have been a
7815 (at least originally) rather than a 7812 as I'd misremembered it.

It's highly likely that I'd simply substituted the 7815 with a 7812 and
a resistor network to lift the common pin by the required 3 volts. The
details of this repair are now marked up on a printed out circuit diagram
packed away in the original box which is now stored in the attic for safe
keeping so I can't be any more precise about the details of the repair
than that.

The 12v battery charging circuit was as crude as can be, relying on the
1.4v drop of a couple of 1N4005 diodes in series to drop the 15v
regulator output to approximately 13.6v - however, the diodes did serve
the secondary function of preventing the battery from back feeding into
the output of the 7815 chip, rather neatly fulfilling two separate
functions in the circuit. I think it was just a matter of dumb luck that
the float charge voltage ended up being 13.5 rather 13.8 volts in this
case.

Having looked at so many of APC's circuit diagrams, I have to say that
I've never seen so ****ely laid out circuit diagrams in all my life as
those (and that's even going by the crap standards of 1960s American
electronic "Schematic diagram" practice!).

I even spotted a few totally illogical wire ups of CMOS 4000 series
logic gates including one case where the output of a dual input gate was
wired to Vcc at 12v. I suppose I could have worked out what "IC2"
actually was if ICBA but life's too short to waste on satisfying mere
idle curiosity.

The one thing about all of these diagrams is that most of the ICs and
discrete semiconductors were simply labelled with an IC or U number with
no BoM listing in sight. However, in many cases I'd spot voltage and
current ratings for diodes and transistors marked against these
components even to the extent of indication Rds values of 0.028 ohms and
50v for the power FETs used in the inverter sections which, to my mind,
could only be BUZ11s (or their equivalent).

If you're trying to repair one of these older UPSes using these diagrams
as a guide, you can usually identify the mystery components on the
diagram by locating the actual components as fitted to the PCB(s) anyway,
so these diagrams aren't entirely useless in this regard (just bloody
difficult to follow and make sense of).

--
Johnny B Good