» A look at standby or off line power protectors «

The Off Line or Standby UPS, also know by the acronym VFD

As mentioned earlier in the article, is it a 'level 3' UPS, just protecting against surges, power sags and power failure.

In simplest terms, this is little more than a battery that takes over when it senses a power cut or surge. This topology is considered 'single-conversion' because at any point in time, power is only being converted once (AC to DC, or DC to AC). In normal operation, a small amount of power is being converted from AC to DC to maintain battery charge.

The 'Off-Line' part refers to the fact the inverter is off and not always in circuit; there is no built-in static bypass switch. These type basically comprises of a small filtering circuit for spikes and surges and an 'off-line' inverter. Typically the voltage flows straight through, within a tolerance of around 25 percent. Above or below this and the microprocessor switches over to the battery to supply the output for the load. This switching time is referred to as transfer time and can be anywhere from 10-20ms, perhaps even better on high-quality models. Some have varying degrees of extra protection on top, which is always a benefit.


Advantages

Low purchase cost
Good efficiency, in terms of power use.

Disadvantages

Only protects against power problems 1-3.
Poor output voltage and frequency regulation.
Short duration back-up time, typically under 5 minutes.
Generally poor or limited monitoring support.
Battery life reduced by frequent switching to battery mode.
Only really useful when you have a solid and consistent mains supply.

Where to use

Smaller, non critical units like home computers or non critical office computers, faxes, speakers etc.

What to look for

Get a line interactive instead.

Personal recommendation:

Get a line interactive instead.