[TriLUG] reason not to mix batteries in UPS

[Joseph Mack NA3T via TriLUG]

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!