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UPS & Car Battery
Name: prosenjit Date: October 22, 2006 at 19:45:05 Pacific OS: Windows XP Prof SP2 CPU/Ram: 1.7 ghz, 256 mb ddr ram Product: 845 glad (intel)
Comment:
I want to connect a 12 volt 120 AH lead-acid car battery with my existing 500 VA UPS, for very fast switch over and long backup time during power failure, i also have an inverter which i want to use for charging the car battery. Question is will the UPS able to draw required power from 12v battery to run my PC. I am trying to do so because my inverter is not so fast as the UPS in terms of switching over but back up is 15 muintes only where inverter and this battery backup time more 3 hrs, 17" AOC monitor, 1.7 ghz p4 cpu
Name: Tubesandwires Date: October 22, 2006 at 20:56:07 Pacific
Reply:
The battery in your UPS has a tiny usable capacity in comparison to that 12v car battery - about 12.5 AH - about 1/10th as much - the car battery would have no problem powering the UPS. In fact if the battery in the UPS is 12v and lead acid you could connect the car battery directly to the UPS and have a huge amount of time it would run on the battery alone. If you wanted to have the battery 100% charged all the time, the invertor would have to have enough amperage output to keep up - at least 4.2 amps. A car battery charger connected to the 12v battery would work too, but you may have to add a filter to it to prevent it from injecting noise you can hear at the computer.
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Response Number 2
Name: Tubesandwires Date: October 22, 2006 at 21:08:42 Pacific
Reply:
If you wanted to have the car battery 100% charged all the time with the AC to the UPS off, a hypothetic situation, .....
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Response Number 3
Name: SkipCox Date: October 22, 2006 at 22:29:07 Pacific
Reply:
Please report back with the results of a gassing battery and/or battery explosion in your home...in other words, forget this project.
Skip
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Response Number 4
Name: wizard-fred Date: October 23, 2006 at 03:10:32 Pacific
Reply:
Actually there is another problem. Unless the backup power is a small fraction of your 500va it would probably fail by overheating before your storage battery gets discharged. If you take a good look inside the UPS you will find the heat sinking is very poor with almost no ventilation. What you propose has been done by people with photovoltaic cells charging storage batteries. They increase the heat sinks and use forced air cooling. You will also have to derate the power as it is rated only for the original backup time. Forget the inverter, when you are onbackup, you won't have AC to charge the battery.
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Old computer needs a job
