Inverter or UPS
By Joseph Parish
Last evening I had a discussion with a like minded individual who felt that he could readily use inverters and UPS units interchangeably. Although the two types of power units may share some similar characteristics they are actual two different “animal”.
A UPS is nothing more then a battery charger which when the electricity is on will maintain a full charge within the enclosed battery. These UPS units are inverters which are connected to the line voltage at all times. When the AC supply source fails the UPS will kick in and continue to providing power until its battery is completely discharged.
UPS units are fairly inexpensive but were not intended to replace an inverter. They generally have an extremely limited storage capacity and are intended merely to provide emergency power to computers until such time as an orderly shut down of your data processing equipment can be accomplished. The goal associated with the UPS is to avoid the loss of computer data when power is interrupted.
Since the peak power capabilities of these units are fairly close to their rated power they should never be employed to start any sort of induction motors. In contrast the DC to AC inverters is designed to provide a continuous power level and in addition can usually be designed for higher peak capacities in order to allow starting small motors.
Inverters are specifically designed to have low consumption when unloaded. These figures generally boarder the low wattage ranges with a built in current detector which activates the high power section during periods of high peak current. The common UPS units do not normally have such functions.
The various UPS units are frequently designed for short time operation and usually contain only a smaller battery which is just enough to cover the time needed to tie up the necessary computer work and shut the system down in a normal manner. They have no provisions for long term operation.
Frequently, an UPS will list their specifications in terms of operating time verses wattage. As an example one specification may state 1 hour @ 300W or maybe 3 hours @ 100W. Essentially what this is telling us is that according to the size of the units battery pack it will provide us with x amount of operating time after the lose of normal line power. They should not be placed in a position where they are expected to perform continuous duty as they will fail. A major feature of the UPS is that once its internal battery is totally worn down the unit will shut off.
Under unusual circumstance you could conceivably use a UPS as a source of continuous power if and only if you have a means to recharging the power source. There are a lot of variables which would come into plat when considering this arrangement such as if a larger external type battery is used the unit may perhaps overheat as a result of the continuous operation environment it is subjected to even if adequate ventilation and cooling fans were provided. Proper fusing would have to be taken into consideration as well. I suppose the bottom line here is to use an inverter where it is called for and employee the UPS for its intended purpose only.
Copyright @2010 Joseph Parish