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- testing power cables
October 9, 2009, 8:31 pm
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what is the best way to test a laptop's power cable?
I recently used a multimeter to test the output from the adapter, there was
no power. I then tested the output from the mains (the cable that goes from
the wall to the adapter. Needless to say, there was a minor explosion as the
power arced to the multimeter pointer. That cable was evidently good! ...
but how do I avoid explosions an electrocutions next time?
Re: testing power cables
If you stick the bare tips of a multimeter lead set, into an
AC outlet of any type, there is a danger of the tips crossing,
and you will indeed have a "mini explosion".
To test cables, you can use the ohms range on the meter.
1) Disconnect the cable from the wall! We don't want any power.
The ohmmeter in the multimeter provides everything needed.
2) Use the ohms range to measure resistance from end to end. Touch a
contact on one end of the cable. Touch the matching contact
on the other end of the cable. Does the resistance read
zero ohms ? Now, move one of the meter leads to the other
contact(s) on the end of the cable. Does the resistance read
"infinity" for those ? Each wire should have continuity from
end to end, but each wire should also be insulated from the
other wires in the power cable.
Any time a measurement includes the possibility of shorting the
meter tips together, then select a different place to make
the measurement. For example, when people work inside a computer,
I tell them to clip the black lead of the meter, to a shiny screw
on the back of the computer. They can then use the red colored lead,
and probe around inside the computer with relative safety. The meter
should be placed on the appropriate DC voltage range for the
measurement to be made. By separating the meter leads, I hope to
prevent the very accident you've had. Note that inside the PC,
there is a possibility of someone shorting +12V power together,
and a similar sparking or burning could result. But not nearly
as energetic as shorting the mains!
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