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?
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. :-(
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.
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Jerry G. =====
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?
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.
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.
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.
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")
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.
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.
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