What are the cons of using an external battery charger for charging my UPS's external batteries while the UPS is on?

I have an inverter/UPS with external battery. I am tired of constant PC reboots caused by power fluctuations in my area.

I have tried finding a solution to the restart issue, but did not get enough solutions posted here: http://www.tomshardware.com/answers/id-3537573/rebooting-power-fluctuations-connected-ups.html

I have 2 PC's; one of them keeps rebooting at power fluctuations. The UPS is working fine.

I am thinking of buying an external battery charger for the external batteries of the UPS.

The UPS will be switched on 24x7. It will get 12 v DC from a charger while the main power supply is available or battery in case of power outage.

Like this:


UPS's mains will be switched off, so UPS will be on 24x7.

Before buying an external charger I would like to make sure that this is a feasible solution. What are the cons of doing so?

1) Will the UPS heat up? (UPS has internal fan to pump out hot air)
2) Will this reduce battery life? If so, by how many years ? (The battery is 1 year old)

The battery I'm using is an exide tubular battery 180ah: http://www.powerwale.com/store/exide-inva-tubular-it-500-plus-150ah-battery/77315

The charger I have in mind is: https://www.amazon.in/12Volts-10Ampere-Alkaline-Automoblie-Inverter/dp/B01C00JDY6?tag=googinhydr18418-21

Currently the UPS runs on battery when the power goes down for 12 hours continuously.

Any thoughts?


The PC only reboots if it is using 100% CPU, i.e. doing some CPU intensive work.

So it looks like when the PC is at 100% load and power drops, the PSU is unable to hold the power for too long, hence reboot.

  • 1
    Why? A UPS should already reduce the power fluctuations. If it is not, it's likely that you're not using the right kind of UPS for the job. Why not get a UPS that actually fulfills your requirements?
    – Seth
    Oct 10, 2017 at 6:15
  • one PC works correctly one reboots., who's at fault ?
    – user176344
    Oct 10, 2017 at 6:16
  • 12 hours? This question is not suitable for SuperUser. Try ServerFault.com. (Maybe NetworkEngineering.SE) What you mention is well beyond typical home equipment. You may want to read about daisy-chaining UPSs. (Simple answer: don't do it.) As requested, those are my thoughts.
    – TOOGAM
    Oct 10, 2017 at 6:17
  • You changed the power supply on your computer and its still broken. As such either the hardware itself might be faulty or you changed your workload. Does your UPS offer you any data on what happens if your PC reboots? Like do you see a dip in voltage supplied by it? Did you check the temperatures of your components? Some of your components might also have aged depending on how long you've had that system. In addition you will see faster degradation if you run consumer components 24/7. You followed the advice on the other thread like the person mentioned I guess.
    – Seth
    Oct 10, 2017 at 6:25
  • @Seth maybe 450watt PSU is not enough ? as both PSU i checked are 450 watts, workload is same, which hardware is faulty ? motherboard ? . UPS does not offer any data, just few LEDs. PC is 2 years old, and UPS is 1 year old. so i am not sure, which componenet is aged. thanks
    – user176344
    Oct 10, 2017 at 6:42

1 Answer 1


The issue you are most likely having is a crappy UPS, with a slow switching speed - slow enough for one of the power supplies to not like it. (If you get a quality new power supply on the device that is not handling it, that could solve your problem).

What you are planning on doing is likely a bad idea (I don't think you have the knowledge to pull it off, and its dangerous).

Bypassing the built in battery charger is unlikely to help you - it is more likely to damage the batteries and won't solve the presenting problem. You will almost certainly find that your UPS is a Line Interactive UPS - if you want to avoid switching times, you probably need to get an Online UPS. These are higher quality devices which don't have a switching time, but cost more to run and are more expensive.

One of the things about Line Interactive UPS's is that they are designed with cheap components, and you will find that it is not designed to run continuously on on battery power.

Also, if your equipment typically pulls more then 120 amps - which is very little for 2 servers - the charger you have won't keep up, and will drain the batteries over time.

You would also be working on equipment which converts safe 12 volts into much more dangerous voltages - often way more then the 240 volt output. You are breaching the safety of the case. This is a recipe for disaster.

  • 2
    On his TomsHardware post he describes that he changed the PSU from the "working" system to the one that is having issues and the issue persists. So I'd assume it's unlikely that a new PSU is going to fix the issue. I agree with everything else.
    – Seth
    Oct 10, 2017 at 8:27
  • online UPS is last option for me., will changing PSU solve it ? like from Corsair VS450 to Corsair VS 550/650. Thanks, one more thing, what is the reason for this happening now, i mean it worked great from last 1 year, but from last 3 months, i am facing this issue.
    – user176344
    Oct 10, 2017 at 9:12
  • The specced switching time for your UPS is 15ms - thats 3 times higher then typical for a line interactive UPS and the core of your problem. If you were an expert you would probably find a dodgy capacitor is the issue starting now. (could be in mb, PSU or UPS). The Corsair VS UPS's are budget upss so will not have large (=expensive) caps to buffer for the switching time. A larger one could help (bigger rating so better caps), but probably won't...
    – davidgo
    Oct 10, 2017 at 18:29
  • Your 2 psus are on the very edge (slightly over) what the UPS can provide. The UPS is specced at 880 watts, each PSU can draw up to about 540 watts (450 watts output at 80% efficiency) - so 1100 watts - so the UPS is to small to handle maximum load. Getting a larger Corsair VX PSU could push this slightly further do not a good choice. Getting a more efficient (= more expensive with usually better components - say 450w 80+ gold) will reduce max power draw and probably have better caps to handle slow switching - but the UPS is still under specced.
    – davidgo
    Oct 10, 2017 at 18:37
  • only one PC works at a time, i dont use both PC at the same time. please check updated question. looks like issue only happens when PC is doing some heavy computing.
    – user176344
    Oct 27, 2017 at 9:00