On Fri, 12 Oct 2012 10:14:58 +0800, who where wrote:

A bit off-(thread)-topic, but I have a $20k+ communicatios test set
that uses Gates cylindrical sealed lead-acid cells in the battery
pack.

Sounds familiar. I have an IFR-1500 that uses those Gates cells.
They're really made for alarm system use, not for a power hungry
1980's service monitor. It would kill off 6 batteries every 2 years
or so. I have up, removed the internal batteries, and run it off a
big gel cell when needed.

The inbuilt charger design was such that these sets seem to
kill packs ina couple of years. Tiring of this recurrent cost, I
rejigged the charging circuit some 12 years ago, and haven't had a
pack die since. Sample of one isn't generally considered
statistically significant, but this is to me.

Good idea. Incidentally, IFR power supply design is just plain weird
and difficult to repair. Mine have been down for many months because
the AC section of the power supply won't play switcher. So far, I've
replaced literally everything that could possibly cause a problem
without results. I'm running it on the DC section which fortunately
still works.

Measure the charge current at various discharge levels and
I suspect you'll find that many UPS's are trying to squeeze the last
bit of power out of their batteries in order to give longer runtime.

Just as laptops do ...

The joy of specmanship. If I'm lucky, and can find a way to reduce
charge current or float voltage limit in software, I can usually
extend the battery life. However, that's often impossible without
inside information or reverse engineering. I see far too many laptops
eat batteries due to overheating and overcharging in laptops that have
never been run on battery power.

They also tend to recharge rather quickly, in order to deal with
repetitive power failures.

Yes, almost universally.

I've often wondered if there's a recharge time spec for UPS's. A few
quick Google searches didn't find anything. I can see why the UPS
manufacturers would want to recharge quickly, but they should at least
give the customer the choice between fast recharge and long battery
life.

I had a running battle with APC over this issue on some of their
products. Note the pile of rack mounted (forgot the model number) APC
UPS's piled up on my deck:
http://802.11junk.com/jeffl/pics/home/slides/BL-house3.html
There were many many more that were ummm... recycled because the
batteries got hot, bulged, and eventually leaked electrolyte all over
the equipment. This UPS used four 12V 7A gel cells in a 24V
series/parallel combination.

I have been called on to "service" quite a number of failed soho UPS'
of varying sizes from 150W to 4kW, mostly APC. The electronics are
almost universally fine - except for one with dead FETs in the
inverter, the failure mode in every single one was batteries. When I
bothered to check the charge regime, it was found to implement the
above rules 1 and 3 on how to kill UPS batteries.

Yep. I've had similar experiences. I don't see many big UPS's but
overcharging is epidemic on small UPS's.

Rhetorical question:
Why are there no UPS's that use Li-Ion batteries?
Spoiler:
http://batteryuniversity.com/learn/article/how_to_prolong_lithium_based_batteries


--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558