• Please review our updated Terms and Rules here

Anyone have any experience adding additional batteries to a UPS system for home use? Lots of info out there but what is safe/smart?

This thread brings back fun memories of the time the 400KVA Liebert UPS we had in the basement datacenter went nuclear and exploded its battery bank.

(I'm fuzzy on the exact details, I wasn't the one who got to talk to the electrician in the aftermath, but my vague recollection was that the series of events went something like: a: street power went out and the UPS, which was technically slightly overloaded with all the crud hanging off it, took over the immediate load while the two minute(ish?) start timer on the generator outside was triggered. b: Generator started, sailed through its warmup, and the signal was sent to the cutover circuitry to feed the generator power into the UPS's input, and c: the street power came back on at exactly that second and *somehow* this resulted in a giant power surge forcing its way through the UPS and caused an instant boilover on a full rack of batteries.

Again, I totally could be garbling the why, but whatever happened it was spectacular and expensive. We're lucky nothing actually caught fire, I guess.)
 
"Problem with doing this on the smaller UPSes especially is they're not designed for continuous duty, they're only designed to run for a few minutes at most with a modest load on them."

This. I've been surprised by the lack of cooling on the smaller APC ones that usually end up cooking the batteries. My NSSI one, if I ever get around to it, has the same problem and could use a fan. My big Elgar (available to a good home) has a 120mm fan for cooling that runs pretty much continuously. And it's got a huge transformer in it. The battery charging (48V) is protected by a 50W 50V stud-mounted zener. Real stone-age reliability, there, right down to the cable lacing.
 
One thing no one else on here has mentioned, if you go down this road you'll want to use deep cycle batteries, not car batteries. When you transition from power to wall power, you want to make sure you have batteries that can survive being completely drained, which car batteries do not tolerate very well. A friend of mine used deep cycle marine batteries, effectively replacing the the regular SLA batteries and boosted the run time of his UPS by quite a bit, and to my knowledge is still using them. His base UPS is an APC 1500VA model.
 
Has anyone started using LiFePO batteries in these yet? I have a solar yard light that uses them and it's been going now for about 5 years. More expensive than lead-acid for sure, but they seem to be very rugged.
 
I've attached UPS charger/inverter boards to "incorrect" batteries before (boat batteries, motorcycle batteries), but what I am using at the moment is a Victron 12v 25a charger/tender (like you'd find in an RV to maintain the house batteries) on a deep cycle marine battery, with one of the infamous "Reliable" brand 3000w inverters (they are cheap, but you have to isolate the ground if you hook them to your household wiring because the ground is center-tapped and you'll blow it up if you bond the ground and "neutral" together).

It would be more efficient and probably a little cheaper to go with 24v, but it's easier to run my ham radio stuff off of 12v.

It maintains my communications, a couple of computers, and a little bit of LED lighting for a couple hours of power outage and through brownouts, without the hassle of dragging the generator out to the service entrance and coaxing it into starting.
 
Good thoughts here; especially that the UPS may get warm depending on the load and how long the battery runtime will be. The simpler you keep it the better. I would not advise just adding two new batteries in series (24V) to the batteries that are already in the unit. I would recommend replacing the ones in the unit with two new fresh batteries in series, or I would replace them with a larger single set in series outside the unit if you need the additional runtime. Batteries in parallel aren't great as they will try to equalize with each other and it is just not a real good configuration which is made worst by not using exact batteries in exact condition.

I ended up picking up a pair of 225AH deep cycle AGM 12V batteries (car sized!) from a guy selling them from a cell phone tower - they were $75 a piece used. They have lasted for many years (maybe 10?) being plugged into a desulfating smart charger. I use them in an underground tornado shelter with an inverter.
 
I've been that road many times.
You can add two batteries in parallel, if you keep the current low enough to avoid overheating when used for longer periods it works fine.
The mismatch in age and size will tend to cause the batteries to self-discharge more quickly when the power is removed, so if you unplug the UPS, disconnect at least one bank of batteries.
No need to worry about battery temps since you are using a low-current device and lead-acid are quite robust that way,
 
You must log in or register to reply here.
Back
Top