http://www.batterybackupguide.com/blog/backup-time-of-a-ups-or-inverter-depends-on-current-or-voltage/ Thu, 17 May 2012 21:02:17 +0000 http://wordpress.org/?v=2.7 hourly 1 http://www.batterybackupguide.com/blog/backup-time-of-a-ups-or-inverter-depends-on-current-or-voltage/comment-page-1/#comment-2200 rowlfe Mon, 07 Sep 2009 23:24:24 +0000 http://www.batterybackupguide.com/blog/backup-time-of-a-ups-or-inverter-depends-on-current-or-voltage/#comment-2200 Depends on BOTH. Power is measured in watts. Watts in a battery powered circuit is current times voltage. The battery contains a fixed number of watts at full charge. As you increase the load on the battery, the voltage drops in proportion to the load, and the current increases with the load. If I have a 120 volt battery, current of 1 amp means 120 watts. If I have a 12 volt battery, it takes 10 amps of current to provide the same 120 watts. The capacity of a battery is listed in ampere-hours (alternative to watts). If the battery says 5AH, then it can supply 1 ampere for 5 hours, and likewise at 10 amps, only 30 minutes. The load on the UPS or inverter is what determines the current drawn form the battery, which also drops the voltage in proportion. With MOST computers, especially with a CRT, it is the monitor drawing the most power. The UPS only needs to power things long enough for you to power down properly and save your work. It is NOT designed to run and supply the computer for more than a short period of time, measured in MINUTES. Rarely will you find a UPS that will provide power for longer than 15-30 minutes. If it does, then it will also have a HUGE battery with a much higher cost. At my last job, the servers were supplied with a smart UPS. The UPS could last for over an hour. If power was lost, it would communicate with the server. The server software would keep an eye on the battery condition reported by the UPS and only do a shutdown if the battery reached a low voltage condition. This smart UPS also cost about $500. A replacement battery (2x12V each about the size of a larger auto battery) was about $300 of the cost. Not cheap... Most consumer devices do NOT communicate with the computer, leaving the task to you to perform an orderly shutdown. Depends on BOTH. Power is measured in watts. Watts in a battery powered circuit is current times voltage. The battery contains a fixed number of watts at full charge. As you increase the load on the battery, the voltage drops in proportion to the load, and the current increases with the load. If I have a 120 volt battery, current of 1 amp means 120 watts. If I have a 12 volt battery, it takes 10 amps of current to provide the same 120 watts. The capacity of a battery is listed in ampere-hours (alternative to watts). If the battery says 5AH, then it can supply 1 ampere for 5 hours, and likewise at 10 amps, only 30 minutes. The load on the UPS or inverter is what determines the current drawn form the battery, which also drops the voltage in proportion. With MOST computers, especially with a CRT, it is the monitor drawing the most power. The UPS only needs to power things long enough for you to power down properly and save your work. It is NOT designed to run and supply the computer for more than a short period of time, measured in MINUTES. Rarely will you find a UPS that will provide power for longer than 15-30 minutes. If it does, then it will also have a HUGE battery with a much higher cost. At my last job, the servers were supplied with a smart UPS. The UPS could last for over an hour. If power was lost, it would communicate with the server. The server software would keep an eye on the battery condition reported by the UPS and only do a shutdown if the battery reached a low voltage condition. This smart UPS also cost about $500. A replacement battery (2×12V each about the size of a larger auto battery) was about $300 of the cost. Not cheap… Most consumer devices do NOT communicate with the computer, leaving the task to you to perform an orderly shutdown.

]]>