How To Add Another Battery In Ups, I want to add another 12V battery in UPS

hi,
can any body tell me, how can i do this safely?
I have a 600va ups for my pc and it gives just 10 min backup, I use cpu and a 15" tft, even though backup time is very short,
So, I am planning to add another 12V leadbattery with current ups, I have decided to connect the new battery with parallel connection to the existing ups battery, means bat1 positivt to bat2 positive and bat1 negative to bat2 negative. I think I should not connect the baterries in series, because it will make a 24 volt batery, as the ups circuit is made to handle 12V only so 24v may hurm the circuit. Am I right?

What is suggested, series connection of battery or parallel
please guide, thanks in advance

Correctomundo.

This presumes your existing UPS battery is 12V. Not 6V or 24V or whatever.

You should be aware that the charger in the UPS may not be up to charging both batteries and may fail at some point.

TOK

Also make sure the heatsinks for the mosfets are actual heatsinks and not just a solid block of aluminum.

basically the idea behind the solid block is that by the time the fet heats up to about 100 Celsius, the battery is dead. if they are solid blocks you don't need to change them, just add a fan.

Well, to be fair, the solid block is a heatsink, they'll absorb a fair bit of heat. Just not a good heat dissipator.

yes Gorgon, you are right, but I want to give it a try, just want to see how it functions, do I really get longer backup time?

This post has been edited by ganesh_guwahati on September 10, 2011 09:18 am

hi, johansen
I see that in UPS circuit, there are 2 big blocks of aluminum working as heat sink, each block is connected to 2 transistor (may be mosfet, as you said), and also I can add a fan to keep them cool,

I want to make the battery connections in such way that, during charging or discharging circuit should not burn out.

I have only heard rumors of increased battery capacity causing the recharge circuitry to burn out, never witnessed it.

Ganesh - I got your PM. There's no need to send people PMs to answer clarifications. You can just answer project details in the thread, that's what it's here for.

To reply, yes, if it's 12V, then you are probably safe just adding it in parallel as you planned.

yep ...
i would be more concerned with the heat rise over the longer haul due to increased capacity by the addition of another battery .

when the unit was designed , it was figured for "X" amount of charge/run time based on the capacity of the battery in WH or AH .
... before things got too hot , the battery would either be fully charged or discharged to the point of the unit becoming non-functional .

What about intermittent brownouts?

The fact that someone owns a UPS generally means they're rather mission-critical stuff. So, if power's coming on and off, you'd think they'd be designed for that, not just one single cycle. You'd think. Not that that has anything to do with how they're built.

A UPS is designed to provide power for very brief periods.

If power is off for a few seconds to a couple of minutes, you can keep running the equipment. Otherwise, it simply gives you time to safely power everything down.

"Mission-critical" systems (military, hospitals, etc.) generally use backup generators if they plan to keep operating.

HI AwesomeMatt,
being new to forums, by mistake I've send you PM

my query was very simple, but the answers are very critical,
don't worry, I like to do experiments
no matter, if I failed I will lose an ups and a battery

and very soon I am going to experiment this and I think after this we can close this thread/post

thanks for all the valuable suggestions
bye

Try it with the extra battery, but keep a close eye on the UPS for overheating, both during power outages & in the first hour of recharging. It may be best to do this with the cover off the first time, so you can determine if any individual components are overheating.
Anything that gets too hot to touch is too hot for safe operation.
Just make sure you remove power from the UPS before touching anything inside. This includes both line power & battery power.

it shouldn't be a problem. here is my setup


two large 135Ah batteries connected to my 1400va UPS. my UPS is a 24v system so my batteries in series. power cables are made from old car booster cables plugged into the old battery cables in the unit. (there are no batteries in the unit anymore, just the two sitting next to it).

with a rough increase in battery capacity of 100Ah and the fact that the setup has been running for about 3 years like this, i doubt you will have any issues. I get two hours of USE on my computer if the power fails. If I shut down the monitor and standby the PC i get more time.

I think the chargers in these things are float chargers with current limiting. mine doesn't complain at all. If anything the unit would flash a bad battery code and shut down the charger if there is too much current draw as it may think the battery has shorted or a cell has gone belly up.

I have a 400W 24V input UPS that I use with a couple car batteries,and it is fine. Didn't overheat,and the charger didn't blow up.

*shrug* Worth a shot,just keep an eye on it the first time you use it.