[ale] OT: question about replacing batteries in a APC UPS

[Mike Harrison]

Courtney asked:
> What and how do the testers reveal ?

  Disclaimer: This is potentially dangerous, don't touch anything metal, 
  don't wear shoes with metal tacks in the heels.. don't.. (it's a long list)


  Good question. Set to AC Volts, (Alternating Current) you can test an 
  outlet as follows:
       
     The outlet should have 3 plugs.. 2 slots, one larger than the other
     and a round hole:

             [ |
              o      
     The larger slot on the left is 'neutral' the smaller one on the right
     is 'line' or 'hot' and the small circle is 'ground'. 

     In a perfect world. 'hot' has a sine wave of approximately 117 volts 
     calculated as a 'root mean square' average of alternating electrical
     potential. You want to make sure it's there, and that 'neutral' is 
     at 0 volts, as is ground.

     So with your el-cheapo voltmeter, stick the probe tip black lead in 
     the 'neutral' and the red lead into 'hot'. You should get 110 to 120 volts AC.
     
     Then move the red lead into 'ground'. You should get 0 volts. Maybe 0.5volts. 
     but it should be 0. Ground and neutral (in most systems) tie into the 
     same place back at the breaker panel.. they should have the same 
     potential. 

     Then move the black lead to 'hot'. You should get 117 volts. If not, 
     your ground is open, not grounded. Very common problem in houses. 
     The purpose of the ground wire is safety. The metal chassis of a 
     device uses the ground wire as a redundant path back to the breaker 
     box. If there is 'leakage' via EMF from high voltage electronics
     or transformers or.. (lots of things), it should drain down the
     ground wire. If it is 'open', a shock potential from the device may 
     exist. Grounds are also a catastrophic failure protection means. 
     If a power supply 'melts down' and shorts to ground, the current 
     should travel back to the break panel at close to 0 volts, and if the
     current level is high enough, allow the breaker to trip. 

     Last test: paranoid mode. If you have something that is grounded 
     handy, like a metal copper pipe that goes into the earth, large metal 
     structural supports.. etc..  - Measure between it and the Ground and 
     Neutral and make sure it's 0 volts or really really close to it. (.5volt?)
     and measure between the natural earth ground and 'hot' you should get 
     110-120 volts.

So.. If all is good, you have a properly wired electrical outlet, there is 
one good 'idiot check' you can make on your UPS:

     Set your meter to Ohms. A measure of electrical resistance. 

     With your UPS unplugged, put the black lead on the round pin. 
     then put the red volt meter lead on any metal on the case. 
     It should be under 1 ohm. Now move the red lead to the round
     plug hole on the outlets. Same thing. 1ohm or less. 

     On some UPS's you MAY be able to do this with 'hot' and 'neutral' on
     the outlet to the cord plug end for hot and neutral, depends
     if it's using a relay for power pass through and what it's position
     is when 'off'. 

Plug your UPS in and turn it on. Repeat the first set of steps for the 
outlets on the UPS.

Last test. turn off the power to the UPS, but keep it plugged in (so 
ground is still attached) so that the UPS is running on batteries. 
It may work better if something is plugged in and running off the UPS
as many of them require a load. Then do the tests again. You will get 
something approximating 110-140 volts from neutral to line on the UPS, it 
depends on the quality of the site wave your UPS generates. It may read 
high if there is no load or a very small one, and/or it produces a squarer 
waveform than normal line power.

----------------

Honest disclaimer: I've done these tests and more.. but I usually 
just plug them in and see if they work. :)  - I did check out the wiring in my house
when I bought it for proper polarity of the pins, and good grounds.. 
and again when I put in the generator and UPS's.. but I'm insane.