Uninterruptible Power Supplies

A UPS is the best solution for any major sag, brownout, or complete power outage. 

There are many different kinds of UPS', but we are going to focus on the main Types according to the IEEE.

Off-Line UPS

Also known as a Standby UPS.  this unit is a battery a switch, a charger circuit and an inverter.  The unit feeds the power directly from the wall to your load.  their is no isolation and no voltage regulation, except for switching to battery.  Every time the voltage goes outside a set parameter, the unit will switch and then the battery will feed the load through the inverter.  This is a very low end box, and because it switches to battery frequently you will find that the battery life is not as long as some other types of UPS'. 

We do not ever suggest using a Off-line UPS to feed a critical load, but an off line unit DOES have its place.  These units are cheap to build, so they are cheap to buy.  They make great back up power units for non critical computer systems that just need cheap runtime.  We at South Bay Supply use off-line UPS' to back up POS systems, so you will have the ability to finish a sale even if the power is off.

Be sure to look at the output of the different UPS' as that can effect what units you choose.

Line Interactive

The line interactive UPS is the mid-range UPS.  This unit is a hybrid standby type unit that still has a switch, batteries, charger, and inverter, but it also has some voltage regulation.  This is generally through the use of a autoformer that will buck or boost the voltage.  The benefit of this is that the input voltage window is set wider, so the unit does not go to battery as frequently.  This means that the battery will traditionally last longer than the batteries in a off-line UPS.  The Line interactive units also tend to have much better communication and software options that can be utilized.

Look for a unit that has a true sine wave output and one that has


The Online UPS is also called a true online, a power conditioning UPS, or a double conversion UPS.  Look closely at the UPS you are buying and look for the term double conversion. 

Some UPS vendors do market what they call online type boxes that are really a hybrid line interactive that has two inverters and two strings of batteries, but it is NOT online/  The reason that the IEEE calls these units online is that the unit converts the AC voltage coming from the wall into DC power that feeds the inverter, and the charging circuit.  The DC is then converted into AC going through the inverter.  Because the inverter is always feeding the load, and the inverter is always on it is called an online unit. 

The benefit of the online unit is that it has no switch time, and it has a perfect sinewave output because the inverter is always feeding the load.  This is the only type of unit you should use for a critical application (with a few exceptions of course). 

Most of the units that South Bay Supply specifies and sells are true online UPS'.  These units are designed to give you clean, uninterrupted power to your load.

The Red Headed Step Children

The IEEE has a few units that fall between the cracks, these are the units that are hybrids of the more traditionally units, that have pros and cons, but are not main stream UPS'.

Ferro-Resonant UPS - This UPS is a line interactive UPS that has a large Ferro Resonant Power conditioner as its core.  These are absolutely great units in industrial areas where there are a preponderance of relays on the output of the UPS.  A great example would be waste water treatment plants, where there are so many valves, pumps, relays, etc. that tend to eat up many other UPS'.  The drawback to the Ferro is the huge amount of heat that Ferro's tend to throw off.  As we all know heat is the enemy of a battery, and a UPS has lots of batteries in it.  For the right situation a Ferro is definitely the way to go.

Delta Conversion Online UPS - This is NOT an online UPS.  This is NOT a line conditioning UPS.  The Delta Conversion Online UPS is a great design to try to get better standard power coning through a line interactive type box.  This is also a great way to get much better efficiency, as the unit is not doing a double conversion.  This box has its place, but not if you have a critical load that needs clean reliable power.  If you want backup power for your computer room, and you want to go the step above line interactive, this might be the option for you.

Click here to see the UPS Vendors and Products that we carry.

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