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Another type of UPS
Authored by: rpost77 on Oct 11, '05 09:44:28AM

One type or UPS you missed out on in your description is the Online or Double Conversion type. These are the most expensive type of UPS you can buy but are (in my opinion) the best type of UPS to go for. You can buy consumer sized Double Conversion type UPS's and you will find that most of the industrial UPS's used (for computer centres etc.) are of this type.

An Online type UPS works by converting the incoming AC to DC power and feeding the batteries. The DC power is then converted back to AC via an inverter to deliver an AC feed to the connected devices. The benefits of this are:-

1) The input and output stages of the UPS are separate so whatever happens at the input end (voltage sag, spike etc.) is kept totally out of the way of what is being delivered at the output end (the output end is always a constant voltage fed via the inverter from the battery circuits no matter if the input is way under or way over voltage) - surge suppression etc. is kept separate from the output feed - AVR type UPS's or buck-and-boost UPS's work differently in that the voltage is under or over compensated for as it tranverses the UPS circuit.

2) The output is a true sine wave output which is 'healthier' for any connected equipment. Most other UPS types do not deliver a true sine wave but a modified sine wave (on a 'scope looks square instead of a flowing line). Although a modified sine wave won't neccesarily harm your equipment, there are arguments that say some sensitive devices don't cope so well with them and it can 'stress' circuitry and lessen a devices lifespan.

3) There is no switchover time when the incoming AC power fails. As the output is fed from the DC float (batteries) via an inverter and thus separated from the AC input, when the AC input fails there is no time period for 'switching' required as in AVR types etc. Although the switching times of other types are fast (milliseconds) there is still potential there for this to cause an interruption to connected devices.

I personally use a Double Conversion type UPS (Sola 610 1KVA - sold as Best 610 in the US and now owned by Powerware - I live in Australia).

When it is time for my current UPS to pass to the UPS graveyard I will be buying another Double Conversion type (I feel the extra expense is worth it for the power quality I get for all my sensitive (expensive!) electronic equipment that is connected).

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UPS Safety and Costs
Authored by: parr on Oct 12, '05 07:37:19PM
A couple of more suggestions, to help you spend your money wisely (and keep it).

1000 to 1200 Watts are required to provide adequate power for many desktop computers. To provide that power the 12 Volt batteries in many medium sized UPS units have at least a 100 AMP fuse! 12 Volts x 100 Amps = 1200 Watts. 100 Amps running through a wire or shorted circuit board can melt or catch fire to many fire "resistant" materials including the case plastics.

After seeing two separate UPS units spontaneously combust due to their internal electronics or batteries shorting out. For fire safety reasons I now only use UPS units in metal cases.

liebert makes nice dual conversion UPS units, In the short term they are some of the more expensive units, but they will make up for it in reduced battery costs and replacement hassles, because of their dual conversion design. They eliminate the cycling of Charging vs. ON Battery stress that many of the lower end UPS units have. Batteries in Liebert UPSs typically last about 5 to 7 Years. Batteries in simpler designed units typically last 2 to 2.5 years. At $75 to $100 bucks a battery change, recycling issues: battery = (LEAD + hydrocloric acid), hassle factor and not to mention the peace of mind. The few extra bucks up front is worth it.

Also remember to test the batteries in your UPS at least yearly.

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