There was mention of reducing the charge voltage of an APC UPS to help reduce the stress on the batteries - however I can't find the thread (sure it was here - I think ...)
Anyway, I have several APC UPSs in need of new batteries and on looking I see only one trim-pot on the pcb - is it likely that this is _the_ one to adjust the charge voltage?
I seem to remember someone saying they had done this and I was wondering if they would be so kind as to tell how.
A google search for schematics or service manuals draws a blank (well nothing useful anyway)
Today is the 5 year battery change date for my alarm. It's got 3 boxes, each with a 7Ah SLA battery. I just tested the batteries which have come out, and one is effectively dead - its capacity is 0.25 Ah, whereas the other two are OK (almost certainly not
7Ah, but not completely dead). I checked the float voltage, and the box with the dead battery is floating at 13.9V, whereas the other two are 13.8V (which is what they all should be). I guess over the 5 years, that extra 0.1V has aged the battery faster.
Leaving my last caravan battery on 13.8v, I think caused its early demise. I now leave the PSU/ charger always on, but disconnect the battery after it has had a suitable period to re charge, then give it an occasional boost.
Its small 3aH-ish alarm SLA battery, is fed via a diode. That has so far survived 10 years. So my conclusion now, is that even 13.8v is too high with a constantly on supply.
It might be on older and bigger (several kVA) UPS's. On modern smaller ones probably not. The trim-pot is hardware mod, see recent post in a new thread for links to start you off.
It was in a thread called "Bl**dy UPS!" (aka "Bloody UPS!" - can we please stop this practice of trying to thinly veil the expletives?) which was started by Dave Plowman on the 6th of this month.
A thread, it turned out, that was about parcel delivery services rather than the more useful subject of UPSes. I and a few others commented on the misleading subject title and we managed to add a few "OT" comments on the subject of UPSes failing to do their job due to to 'surprisingly short battery service life' which raised the question of float charging voltages.
I might be able to help if you can supply the model numbers. Several years ago (about 6 or 7 is the best I can work out) I downloaded a whole bunch of APC circuit diagrams and manuals covering not only the BackUPS500 and the SmarUPS2000 I was particularly interested in but quite a few others as well.
Unfortunately, the filenames on the PDFs stored by the ftp server archive don't bear any obvious resemblence to the model numbers (hence my downloading _everything_ in sight - Grab it while you can!).
That would have been me.
I'm not surprised. I remember having great difficulty tracking down the APC diagrams collection at the time (about 6 or 7 years back, afaicr). It took quite a bit of determined sleuthing before I "Hit Paydirt" in the form of an ftp archive). Unfortunately, I don't appear to have bookmarked the ftp site.
If I were you, I'd be inclined to take a careful note of the trimpot's setting and try tweaking it whilst monitoring the battery voltage. Whilst this might result in an unwanted change elsewhere (trip voltages/currents or WHY), being able to restore it to with 3 or
4 degrees of its original setting will be accurate enough.
The trimpots are used to only make a very small percentage alteration between the extreme settings points so that restoring back to the original setting by eye will be close enough to get it within a fraction of a percent of whatever it is you're adjusting.
No, you don't reduce the charge voltage, you kill the routine that APS has in testing the batteries to destruction every fortnight. They'll last much much longer that way.
I switched the "battery test" feature off several sets of bateries ago. It did make a bit of difference but not a great amount. Having the batteries sat with 13.8 V charge voltage at 40 C is much more of a killer.
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