Greetings Posted December 7, 2013 Report Share Posted December 7, 2013 (edited) Got a problem with my UPS. It's got two dry 12V 7.2Ah batteries connected in series so it's working on a 24V system. Recently I've noticed it won't hold my PC during a power cut for more than about 30 seconds. I assumed this was something to do with the batteries. So I replaced one of the batteries with a 85Ah 12V car battery. This didn't help at all (why?). I then checked the charge and all the batteries - both 12V 7.2Ah which I assumed were dead and the 85Ah are showing over 12V charge. Despite this, the UPS is shutting down. This would suggest to me that the problem is elsewhere? Does anyone on here know how a UPS works and what component might be broken? Or perhaps both batteries need to be replaced? edit: further troubleshooting: - Charging at 26V - Will cope with 300W power use for a few seconds - During those few seconds charge drops quickly from around 24V to 21-22V and the power supply switches off. Would 21-22V be insufficient to power any appliance connected to the power supply? If so, how is one supposed to use the full charge of the battery if a 10% drop in voltage already deems the whole thing useless? Edited December 7, 2013 by Greetings Quote Link to comment Share on other sites More sharing options...
monkeyseemonkeydo Posted December 7, 2013 Report Share Posted December 7, 2013 Our mains voltage is 230V so a 24V supply wouldn't do much if a standard PC was plugged into it... Quote Link to comment Share on other sites More sharing options...
Greetings Posted December 7, 2013 Author Report Share Posted December 7, 2013 Our mains voltage is 230V so a 24V supply wouldn't do much if a standard PC was plugged into it... Do you even know what a UPS is? Quote Link to comment Share on other sites More sharing options...
*gentlydoesit Posted December 7, 2013 Report Share Posted December 7, 2013 (edited) No but anything with a battery backup has a charge/switchover circuit, and it sounds like the fault may be there. I'd go with the voltage drop being due to load, it the m/A that will give it its longevity during use Edited December 7, 2013 by f**megently Quote Link to comment Share on other sites More sharing options...
monkeyseemonkeydo Posted December 7, 2013 Report Share Posted December 7, 2013 Ah ok, inverter included in the circuit- the way you described it you were seeing 21-22V at the outlet which would never cut it. Quote Link to comment Share on other sites More sharing options...
Kevinfor Posted December 7, 2013 Report Share Posted December 7, 2013 (edited) Been a while since I messed about with computer stuff but I'm pretty sure 300W is nowhere near enough to run a modern computer. Silly me forgot what a UPS is.... A UPS is NOT meant to keep your computer running for very long, 30 sec sounds like a good UPS as the purpose of a UPS is to give you enough time to safely save what you're doing. Edited December 7, 2013 by Kevinfor Quote Link to comment Share on other sites More sharing options...
Martin Reynolds Posted December 7, 2013 Report Share Posted December 7, 2013 Been a while since I messed about with computer stuff but I'm pretty sure 300W is nowhere near enough to run a modern computer. Silly me forgot what a UPS is.... A UPS is NOT meant to keep your computer running for very long, 30 sec sounds like a good UPS as the purpose of a UPS is to give you enough time to safely save what you're doing. 300w is plenty to run most off the shelf computers to be honest. Also, even single battery ups's will run computers for 20/30+minutes. Greetings, what ups is it? All the ones i work with have USB/Serial interface, so you'd beable to connect it to your computer that way, and look into why its not working properly. Quote Link to comment Share on other sites More sharing options...
Danny Posted December 7, 2013 Report Share Posted December 7, 2013 I'm guessing the UPS has some battery management circuitry and changing the battery for something non standard has probably confused it. Quote Link to comment Share on other sites More sharing options...
Greetings Posted December 7, 2013 Author Report Share Posted December 7, 2013 (edited) 300w is plenty to run most off the shelf computers to be honest. Also, even single battery ups's will run computers for 20/30+minutes. Greetings, what ups is it? All the ones i work with have USB/Serial interface, so you'd beable to connect it to your computer that way, and look into why its not working properly. It's a Fideltronik, local produce as far as I'm aware. I would have thought 300W is enough too. I tested it on a 240W+60W lamp. I'm aware it's supposed to give me just enough time to switch the PC off and in current condition it's ok for that. However, it'll do it once and then need a few hours to recharge. Our generator takes about 15s to start and during bad weather it might start/switch off a few times each hour. This means the UPS needs to keep my PC running for at least 1-2 minutes per hour. According to manufacturer specs, it's a 700VA 420W and it should keep the PC running for 110min at 100VA, down to 6min at 700VA. Apparently using a car battery is ok but I think I'll try to get replacement gel batteries and see if that helps. According to some info I found, the batteries should supply a minimum of 13.5V. In my case the voltage very quickly drops to about 11 per battery and the UPS fails. Would such quick discharge not indicate bad batteries? Edited December 7, 2013 by Greetings Quote Link to comment Share on other sites More sharing options...
manuel Posted December 7, 2013 Report Share Posted December 7, 2013 24x7.2 = 172.8wh ? So surely even if the inverter was 100% efficient you would only be getting 34minutes at 300W ? Also - if you only replaced one of your batteries and the other was pretty knackered as well, the voltage would drop fast as the bad ones voltage collapsed and the ups would probably cut out to protect itself from over discharge. From what you say about how often the ups is having to supply a significant amount of energy, it's likely that you are going to go through batteries at a fairly decent rate ? Quote Link to comment Share on other sites More sharing options...
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