I'm testing out some APC Smart-UPS models: the SMT750IC (2023 and 2024) and the SMT1500IC (2024). APC claims that these units have a recharge time of about 3 hours, presumably to reach around 90% capacity. However, my observations indicate that the charging times are significantly longer. For the SMT750IC, it seems to charge roughly 1% every 6 minutes from 75% to 90%, while the SMT1500IC charges 1% every 8 minutes from 55% to 90%. This means the 1500IC took over 4.5 hours to charge from 50% to 90%, and the 750IC was only marginally faster. Given these results, I wonder if I'm overlooking something. Is it possible to have three faulty units?
7 Answers
You’re right; the times listed by APC are likely just estimates and can fluctuate quite a bit.
What voltage are you using: 110 or 220? That can also affect charging times. There might be limitations on how much current the APC allows based on its settings, or the batteries could be older than the unit expects, affecting performance.
Charging times for lead-acid batteries aren't linear; they follow a curve as they approach full charge. Have you considered how many deep discharge cycles your batteries have gone through? Their age might also be a factor in charging performance. Also, doing a quick search on "lead acid charging profile" could give you a clearer picture of what to expect.
Just to add, the charging profile can vary significantly depending on the battery's condition!
Don't stress too much about it. Lead-acid batteries often charge slowly, usually around a C/10 rate. Typically, you don't want to discharge them below 50%, and much less ideally, so they might be accounting for that in their estimates. Also, a lot of that charge time is spent in the topping phase, which can feel slow.
From what I've gathered, they usually indicate a 'typical' charge time in their datasheets. With so many variables affecting battery charging, it's tough to outright declare it a false claim. They're probably just working off a general formula for battery size and input wattage. Plus, charging times are often overlooked in real-world scenarios where the UPS is under load, so it can be misleading on paper.
APC’s numbers are just rough estimates, much like getting a contractor’s quote for home repairs. The actual time could vary significantly based on the conditions and battery specs.
Just checking—was your testing done without any load on the UPS? It’s crucial because that can heavily impact charging times. Marketing figures are often given under ideal conditions, which we rarely replicate in real usage. I actually want to try unplugging two identical UPSs, one minimal load and the other more heavily loaded, to see the difference firsthand!
That's a solid idea! Maybe I'll put a space heater on one to check how that affects it.
Totally! I've noticed substantial differences based on the load.
Good point! I'm curious about how many cycles they've been through too. Older batteries can definitely slow things down.