Hacking UPS

I have a 650VA APC UPS (Back-UPS Pro 650)
that has worn batteries (occasionally, it starts to
beep and the red battery light comes ON) .
The UPS is there to ride through brownouts and
outages lasting usually less than 10 seconds (have
quite a few of those) so if the batteries are less
than perfect, I don't care as long as it can last for
10 - 20 seconds.

So, how does the UPS's circuitry determines if
the battery is going bad? Is it simply a voltage
measurement, or something more sophisticated?
How difficult would be to modify the UPS to
lower the treshold for a bad battery?

Alternatively, how would the unit work if I were
to connect a marine or car battery instead of
the manufacturer supplied battery?

TIA

 

Generally, just fine.
If you put a much bigger battery in, you have to be careful of
overheating due to the extended runtime.

Old car battery from scrapyard is a really cheap way.
Altering thresholds won't do much.

 

It will probably work. Beware though with the sealed batteries. An APC
UPS will shut down when the batteries are completely worn out.

 

Mainly for safety reasons you should be using the proper battery. The UPS
checks the battery by analysing the current load by pulsing it, and reading
back the decay factor.

If you start messing around by trying batteries that are not properly rated
for it, there will be very little dependability. Also, if you put a battery
with too high an amp hour rating, it will not get charged properly, and the
result may be in damaging the UPS.

As for protecting your investment, it is a bit skimpy for my taste that
someone would not at least put in the proper battery in to their UPS.

--

Jerry G.
=====

I have a 650VA APC UPS (Back-UPS Pro 650)
that has worn batteries (occasionally, it starts to
beep and the red battery light comes ON) .
The UPS is there to ride through brownouts and
outages lasting usually less than 10 seconds (have
quite a few of those) so if the batteries are less
than perfect, I don't care as long as it can last for
10 - 20 seconds.

So, how does the UPS's circuitry determines if
the battery is going bad? Is it simply a voltage
measurement, or something more sophisticated?
How difficult would be to modify the UPS to
lower the treshold for a bad battery?

Alternatively, how would the unit work if I were
to connect a marine or car battery instead of
the manufacturer supplied battery?

TIA

 

Just be sure to put it in a plastic battery box, car batteries, particularly
old ones are notorious for spilling leaking fluid if tilted, jostled or
overcharged. Can make a real mess of carpet and subflooring real quick. A
sealed deap cycle marine gel cell would be ideal.

 

It should charge just fine, it'll just take longer to fully charge.
Lead-acid batteries aren't particularly sensitive. The proper battery for a
UPS can be pricey, I have an old Trip-Lite that uses an odd size and it
would have been around $100 to replace it, so I installed a pair of somewhat
smaller surplus gel cells and it's been working flawlessly for several
years. I say go for it and experiment, just use common sense with the wiring
so you don't burn the house down.

 

Hi Jerry,

This brings up a whole other question: Are there any low cost UPS that
do use external 12V or 24V batteries? Or where you can add capacity by
external connection? I know there are industrial ones but most are way
out of price range for PC use. This would be nice to ride out longer
outages without stopping work on the PC.

We have an inverter 'mini suitcase' that is used for the fans of a wood
stove in case power goes after we just put a load in the stove. This
inverter with battery isn't a UPS but just a trickle-charged standby
unit. Kept on the shelf just in case, like flashlights, bottled water
and other emergency gear. It does, however, allow the connection of a
large 12V battery for extended runtime.

Regards, Joerg

 

I have several modded APC Smart UPS's

Add rear contacts fused and parallel to the internal batteries.
Then you can add any batteries you like as long as the voltage matches the
originals. If you are extending the runtime, very good if you fit a fan to
the grill inside, to cool the ccts inside.
I have a smart APC 1500. It will run at 90% load for 8 hours. No problems at
all.
P.S I use 4 x exteral Chloride 100AH in a seriel parallel combo to give the
needed 24v nominal.

 

Thanks for all who replied. I looked up the pricing on
replacement batteries and found them kinda high for the
capacity I'd get. Obviously, if I install external batteries,
they'll be installed in a way that even if they leak, they
can't cause much damage (crawl space ;-) . I'll also put
in a fan that will turn ON if it the UPS is running on battery
power, or charging the batteries.

BTW, how do these sealed batteries degrade? Is it sulfating,
or something else? Is there any way to reverse it to some
degree, like charging it with a slightly higher current and/or
voltage, or pulsing it? Again, if the batteries are not 100%
and I only get half of the runtime -- I don't care. But waking
up in the middle of the night because my UPS is beeping
can be highly irritating. :-(

 

That, of course, depends on the UPS. Some just
watch the potential at the battery REGARDLESS
OF LOAD. Others apply a fixed (known) load and
note how the battery voltage changes. Others
*measure* the load and note the rate of change
of battery voltage. Etc. The Back-UPS 650 Pro isn't
a particularly "high end" unit so I wouldn't expect
much sophistication, there. I'll have to look at the
schematic to see what facilities *are* available to
determine battery state...

Again, it depends on the UPS and the battery chosen.
Let's assume we stick with the same battery *technology*
(i.e. lead acid) so you don't have to address differences in
charging techniques, discharge characteristics, etc.

Typically, the rate a battery is charged is related to the
capacity of the battery. C/10 and C/20 are common
rates. The higher rate obviously leads to greater
*perceived* convenience though usually is tougher
on the battery itself.

One of the risks you run when replacing a battery with
one of a different capacity (physical volume is a rough
parallel to actual capacity -- for a given number of cells)
is that the charger is probably designed with the
*assumption* that a particular battery (capacity) is in place.
Replacing it with a smaller battery could lead to excessive
heating (in the battery) as the battery is now being charged
at a "higher than typical rate". Replacing it with a larger
(capacity) battery could lead to lengthier charge times.

In either case, if the UPS monitors the charge cycle actively,
it can erroneously deduce a battery failure ("Why is this
battery taking so long to charge?" or "Wow! That battery charged
awfully fast! I wonder if that's just a surface charge...")

Using a "car battery" always poses the risk of outgasing which,
if not vented well, can be a fire hazzard. Also, you have to
worry about leaks, spills, etc. as these are not gelled electrolytes.
And, of course, maintenance if the cells are not "mainetenance free".

I had a 3500W unit that ran off 120VDC. I considered using
a set of (10) auto batteries as a cheap way of getting "capacity".
Of course, 10 batteries aren't likely to fit in the living area.
And, with the high charge rate that the UPS used, I was
fearful of putting them in the garage -- 10 batteries potentially
venting into an enclosed space with open sources of ignition
(think gas water heater, automobile, etc.) seemed like an
insurance claim waiting to happen!

So, the only real alternative would be to locate the batteries
outside the garage and run 120VDC through the wall. Then,
run AC from the UPS into the house to support the loads.

But, that means building a shelter to keep the batteries out of the
sun, rain, etc. And, protecting against wildlife chewing on
the wiring, etc. Way too much work!

So, I now use lots of little UPS's. Since outright *outages* here are
rare (a bigger concern are the "2 second wink-outs" you mentioned),
a 500VA - 650VA unit by each critical load is quite adequate.
And, when the machine in question is powered off, there is no
need for the UPS to run at all! (A 3500W UPS wastes a LOT
of power just *idling*!)

The Back-UPS 650 Pro *wants* an 11AHr battery (based on volume).
But, a nice 7AHr will do just fine for you (though you will have to
"pad" it a bit to prevent it from flopping around inside). At most,
that should run you $15 - $18. I think you can even buy the 11AHr
battery for around $20 ("off brand").

What is an outage -- even a 2 second "reboot" -- worth to you?
If it is NOT worth $18, then why are you bothering with a UPS
at all?? (sort of like the folks who spend $50 on a tape backup
system -- that they only use once a month -- and then complain
when they have had a crash and discover last backup they made
is "unreliable")

<shrug>

--don

 

One of the 12 cells of your batteries was overcharged - and is
destroyed. Unfortunately you can not replace this cell in a sealed lead
acid battery. Other methods of repairing it are not possible.
Batteries in UPS degrade mostly because the cells are not balanced.
All are connected in series, and over time the voltage over the cells
is getting different - because of little mechanical or chemical
differences in each cell.
You can increase the lifetime by lowering the charge voltage. Normally
this is 2.3 volts per cell (or 27.4 for 12). Lowering this to 2.27 will
reduce the available capacity a little, but the lifetime a lot.
But the problem is - how can it be changed in the UPS?

Another way would be a balancing circuit for each cell (ensure that
each cell has no more than 2.3 volts). But with the sealed batteries
you have no access to the connectors of each cell.

Sulfating is another issue, but this takes much longer at room
temperature. I have a torch with a sealed lead acid battery that I
charge once a year. It is still ok! The sulfating is also regularly
removed by the test cycle of the UPS (if there is any) or some drop
outs.

M.

 

Thanks for the great replies!! Very enlightening.

I'll take apart the misbahaving UPS and check the
batteries. If there's one that's a lot worse than the
other 3, I'll probably replace it. If it's just a little
worse than the others, I'll try to get a smaller (like
1/3 - 1/2 capacity lead-acid) and parallel with it.
If all are equally bad, I might just need to bite the bullet.

I know that replacing/paralelling one is not a proper
thing, but if Matthias is right, the UPS probably has
1 bad and 3 OK batteries. When I have 3 bad ones,
I'll replace them all. I have another one of the same
UPS, so I might use those extra batteries left
over when all old ones are replaced.

I'll also look into a few other things when the UPS
is open, like slightly decreasing the charging voltage,
or making it more tolerant to marginal batteries.
Assuming I can reverse engineer,or understand the
circuit, which could be very difficult if it uses too much
custom, or VLSI ICs.