[kwlug-disc] UPS sized battery purchasing locally?

[John Johnson]

On 2014-06-01 18:24, unsolicited wrote:
> ... cause I wanted pure sine out ...

While not questioning your requirements I will take this as a jumping 
off point for this discussion.

The output of some UPSes is, as you noted, not a sine wave. For these 
types of UPSes the output s is generated by a rectangular pules in 
opposite polarities.
The amplitude of the pulses is usually fixed. The width of the pulses 
are modified in a Pulse Width Modulated manner such that the resulting 
power curve approaches the nominal 110 Vac.

Note, I said "power curve" as this implies both supply voltage and load 
current.

The voltage and current are specified in RMS - Root Mean Square - while 
not mathematically exactly an "average" can be thought of as such.

The nominal 100 Vac sometimes called 117 Vac or 120 Vac has a wide 
tolerance, ranging from about 90 Vac to something around 126 Vac.
I would expect that UPSes are calibrated to supply their output at the 
low end of this range.

For most equipment this synthesized ac voltage supply is perfectly OK.
(Even for a "shaded-pole" AC motor. Personally, tested and verified.)

Pure sine wave AC is important for some synchronous motors.

jsquared






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