Expert: cleggsan - 12/19/2006

Question
I do not really understand the answer for nomber 1.Could you clarify?...from loading the output........

1.  Short circuit:  From shorted plates inside a wet cell battery.  From loading the output with short circuit load - for instance, when the device being powered has a shorted out power supply.




The text above is a follow-up to ...

-----Question-----
Questions regarding UPS

1.There are many causes can make the inverter in UPS to fail.Among them are overload and short circuit.My question is how can these two failures happen ie the main causes and the effects to the UPS?


2.How can a battery plate be shorted to the next plate.And how can a battery be overloaded?

3.For a UPS system with neutral connected to the main earth neutral,any fault at the main neutral will also cause the UPS not to function?If let say there is a short to earth failure, since UPS is connected, UPS also will 'trip'?

4.Normal output current for overload
0..1min   150%
1..10min   125%
1 sec   1000%
What does these mean?

-----Answer-----
http://www.ybet.be/en-hardware-2-12/ups.htm

The above may help with an overview of ups functionality.  Even though this is a European web site, the principles are the same and it is a good tutorial on the many types and styles of ups designs and applications.

1.  Short circuit:  From shorted plates inside a wet cell battery.  From loading the output with short circuit load - for instance, when the device being powered has a shorted out power supply.

2.  Plate shorts are when the insulating materials are worn down and the plate swells in size to the point of touching each other. These conditions happen with age - and poorly constructed plate arrangement during manufacturing.

3.  Yes.  Is there a question here?

4.  Ratings for overload; that which if you go beyond it is over the capability of the unit as it is designed to sustain such current level.

Hope this helps.

Cleggsan  

Answer
A short circuit is an overload.  The most sever overload since the load impedance is "zero".

Any load on the output of the UPS that causes the impedances to drop below the rated levels and call upon excessive currents is an overload.

Short term overloads are given in your item 4.  So anything exceeding those characteristics can cause overload failures.