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From: Don Y <blockedofcourse@foo.invalid>
Newsgroups: sci.electronics.design
Subject: Re: Cascading UPSs
Date: Fri, 10 Jan 2025 16:52:12 -0700
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On 1/10/2025 3:14 PM, Carlos E.R. wrote:
> On 2025-01-08 07:05, Don Y wrote:
> 
> ...
> 
>> It seems that the UPS makers must rely on battery sales for their livelihood,
>> given the number of discards I find.  And, they have virtually *no* recycle
>> value (batteries are ~20c/lb and the rest of the unit is worth < $5 for the
>> minimal electronics, transformer and steel case)
> 
> Some units kill batteries faster than others.

APCs tend to drift, over time.  So, they end up charging to a cell
voltage that is too high and "cook" the batteries.  Because the
reference drifts, the software doesn't know what is happening
to the batteries.

Also, folks who replace one (or two or three) instead of ALL of the
batteries in the pack just accelerate the problem.

Even if the user IGNORES the "replace battery" alert, the software should
still take steps to prevent dumping charge into a battery that is now
toast (causing it to swell and get stuck in the case).

> It happens when they leave them permanently charging, theoretically to 100%. 
> Others fully stop the charger and leave the battery alone for hours. With this 
> method, unless there are mains failures, the battery last 5 years instead of 2

One can argue that the batteries should be recharged as quickly as
possible -- to be able to provide the stated carrying time if another
outage occurs in, e.g., < 10 hours.  OTOH, a gentler approach might
increase longevity at the expense of risk in the short term.

The fact that the device is powered on "forever" means it SHOULD be able
to learn about the environment in which it has been deployed.  But, these
devices tend to have dinky little MCUs running the show... as if they
were just bits of (dumb) hardware.

[It is sorely tempting to reverse engineer the code in one of their
controllers just to see how naively it has been implemented!]