On 2/10/24 13:40, Joe wrote:
On Sat, 10 Feb 2024 16:45:29 +0100
hw <h...@adminart.net> wrote:
The cheap APC models seem to produce a lot more heat, and their
batteries don't seem to last as long. They work and they're not
really a good deal. I don't have test equipment for UPCs, but you can
feel how warm they get and see how cheaply they're built without
special equipment.
It's quite surprising how many complaints about swollen UPS batteries
there are around the Net. Given the fairly light duties of the batteries
almost all of the time, this is pretty well certain to be caused by
overheating due to incompetent charging. Batteries, particularly
lead-acid types, are not exactly new technology, and the correct
charging of them is well understood.
You have an excellent view of the problem. One of the problems with PBa
batteries is the each one of the gender has a mind of its own, and If
you don't fiddle with the charging circuit, you will never find the
optimum voltage to charge that battery to. One of the things you never
ever want to is look into a liquid acid battery and see it bubbling.
That indicates and overcharge, the bubbling is the disassociated
hydrogen and oxygen of the water component of the acid, which makes the
water go away, leaving eve stronger acid.. Two instances I can regale
you with.
1. shortly after I became the resident engineer at KXNE in NE Nebraska
in '69, the two big truck batteries that started the 150 kw Cummins
standby power failed, basically burned up from over charge. Replacing
the batteries, they boiled like crazy. So I turn down the curent from a
charger with a higher resistor, because it was banging over 2 amps into
the 2 of then to get the 24 the starter needed but that was holding
those up to around 29 volts. The next day I raised the resistor about 4x
as they were still boiling. Wash, rinse, repeat till the trickle charge
was down to around .005 amps. This was all it took for a trickle charge
for a pair of 225ah large car batteries kept clean. 8 years later I'm
bored out of my skull and had an offer to be the Chief at a station in
NM, offering a 175% raise so I took it. Those batteries were then 8
years old, and still were trying to turn that 335 Cummins wrong side out
starting it. When the weekly 15 minute exercise came up you heard the
bendix slam into the flywheel, followed milliseconds later by the first
bark, and 1 measly second later the lights were back on
2. While in Nebraska, it can get pretty cold, like -35F once in a while.
I had put an ambulance alternator in my daily driver, and made a
switching regulator for the voltage regulator but in series with the
voltage reference zener diode, I added 4 common si rectifier diodes to
use their negative temp effects to turn it up or down according to the
underhood temps. 15 seconds after a -25F start, it had the battery back
up to about 16 volts, but 20 minutes and 20 miles later it was down to
abound 12.7 volts, and on a 105F day down to around 12.3 volts. That
battery was then about 7 years old, still had its original water in it,
spun the engine faster than it idled, when the missus threw a rod. The
only thing I didn't get a chance to salvage was that alternator, the
missus sold it to a junk yard the next day before I had a chance to pull
it off.
Getting to know the battery and how to treat it could bankrupt all the
replacement battery makers. The acid SG is important, reject any battery
whose label says SG is 1.280. buy the one that says 1.260, It will be a
fraction of a volt lower, but treated right will actually live years
longer. Modern gel cell's are even more quickly destroyed by over charging.
Your trivia factoid for the day, from somebody who understands the
chemistry.
Cheers, Gene Heskett, CET.
--
"There are four boxes to be used in defense of liberty:
soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author, 1940)
If we desire respect for the law, we must first make the law respectable.
- Louis D. Brandeis
