[TriLUG] reason not to mix batteries in UPS

[Christopher Baldwin via TriLUG]

If you want more things to learn, and potentially a bad idea - I have a APC
Back-UPS RS 1500, with reasonably fresh batteries, that won’t charge. Most
likely a bad capacitor, but I don’t have the skills (or time) to fix it.
Different battery chemistry, some soldering, and maybe lots of magic smoke
- free to a good home :P

-Chris

On Mon, Jan 9, 2023 at 10:21 AM Joseph Mack NA3T via TriLUG <
trilug at trilug.org> wrote:

> On Mon, 9 Jan 2023, David Burton wrote:
>
> > Joe, the LiFePO4 batteries are a different chemistry (only 3.2v per
> cell),
>
> Thanks. Didn't know that. (Just what I need - another battery chemistry to
> learn)
>
> > and should have much better lifespan than the 3.7v per cell Li-ion and
> LiPo
> > "lithium" batteries commonly used in things like mobile phones.
>
> from
>
> https://en.wikipedia.org/wiki/Lithium_iron_phosphate_battery
>
> "
> Because of the nominal 3.2 V output, four cells can be placed in series
> for a nominal voltage of 12.8 V. This comes close to the nominal voltage
> of six-cell lead-acid batteries. Along with the good safety
> characteristics of LFP batteries, this makes LFP a good potential
> replacement for lead-acid batteries in applications such as automotive and
> solar applications, provided the charging systems are adapted not to
> damage the LFP cells through excessive charging voltages (beyond 3.6 volts
> DC per cell while under charge), temperature-based voltage compensation,
> equalisation attempts or continuous trickle charging. The LFP cells must
> be at least balanced initially before the pack is assembled and a
> protection system also needs to be implemented to ensure no cell can be
> discharged below a voltage of 2.5 V or severe damage will occur in most
> instances, due to irreversible deintercalation of LiFePO4 into FePO4.[36]
> "
>
> > However, it doesn't look like this Howell battery
> > <
> https://www.amazon.com/dp/B095K38M6C/ref=redir_mobile_desktop?_encoding=UTF8&psc=1&ref=ppx_pop_mob_b_asin_title
> >
> > is a good choice for a UPS.
>
> Unfortunately no.
>
> The wikipedia page says you get a lot more life than with the standard
> LiCo battery in cell phones. So maybe I would get more than 2yrs from a
> LiFePO4.
>
> One of the reviewers complained about the batteries being made in China.
> However all the LiFePO4 batteries are being made in China.
>
> > If you size your UPS large enough to provide a full hour of runtime from
> > the battery, that would be adequate for your application. 12V × 7A = 84W.
> > If we optimistically assume 80% conversion efficiency by the inverter,,
> > that gives us 0.8 × 84W = 67W usable. So if your load is more than that,
> > your UPS will probably not be able to support it, with that Howell
> battery.
>
> I'm not trying for an hour.
>
> We have two types of power outages here, about 1 sec, where all the house
> clocks reset to flashing 00:00 or else out for hours. I have 4 UPSs. In a
> power outage, the whole house is beeping. If power goes out for more than
> a minute I have to assume that it's going down for a while and I start an
> orderly shutdown. With the UPSs having batteries of random age, between
> 0-2yrs, at least one of the UPSs is near end of life, so I can't wait too
> long. I did a pull-the-plug test on a new set of batteries, to find I get
> about 15mins of power.
>
> Really then all I get for my UPSs is to ride through the 1 sec power
> outages. Any more than that I have to shut down.
>
> Joe
>
> --
> Joseph Mack NA3T EME(B,D), FM05lw North Carolina
> Don't upgrade a working machine - it won't work any
> better - it could work worse; it may not work at all.
> Homepage http://www.austintek.com/ It's GNU/Linux!
> --
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