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I have a 19V 2.1 amp (power mentioned is 45 watt) laptop adapter connected to a 19V 2 amp laptop (in description power mentioned 10.2 watt).

When I plug the adapter, the multimeter shows the rated voltage, 19V. But when I connect it to the laptop, it does not charge. Then when I remove it and check the voltage, it does not even show 1 V; somewhere around 200mV.

What and where is the cause?

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closed as off-topic by Leon Heller, JYelton, Chetan Bhargava, Daniel Grillo, Matt Young Aug 29 '14 at 14:31

This question appears to be off-topic. The users who voted to close gave this specific reason:

  • "Questions on the use of electronic devices are off-topic as this site is intended specifically for questions on electronics design." – Leon Heller, Chetan Bhargava, Daniel Grillo, Matt Young
If this question can be reworded to fit the rules in the help center, please edit the question.

  • \$\begingroup\$ Is the plug polarity correct? (What happens to the voltage of the computer?) \$\endgroup\$ – George Herold Aug 28 '14 at 19:53
  • \$\begingroup\$ the inlet for the laptop is very small. so i took a diff adapter and sliced and joined with a small pin. the adapter had red and white wires and pin had red and black wires. joined black and white, red and red. \$\endgroup\$ – arjun Aug 29 '14 at 12:16
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What is the cause? and where is the cause.

Impossible to know based on the information given. It could be any number of reasons. Most likely, you're triggering a resettable fuse in the power adapter due to an over-current situation when you plug it into your laptop. Possible causes could be:

  1. The power adapter's plug has reverse polarity relative to the laptop.
  2. The power adapter is faulty and is shorting internally.
  3. The laptop's power receptacle is faulty (maybe a piece of metal is jammed in there or a pin is bent).

Also, your power numbers are a little funny. A power supply rated at 19V and 2.1A has a maximum capacity of 39.9W, not 45W.

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  • \$\begingroup\$ And a power supply rated 19V 2A gives 38.0W not 10.2W. If it is really only a 10.2W power supply then it's only putting out one fourth the requirements of the laptop which expects a 45W (or 39.9W) power supply. Possibly the laptop is tripping a fuse in the second adapter simply by trying to draw more current than it can provide. \$\endgroup\$ – Matt B. Aug 28 '14 at 20:15
  • \$\begingroup\$ I like the reset-able poly fuse idea. \$\endgroup\$ – George Herold Aug 29 '14 at 2:00
  • \$\begingroup\$ The power adapter's plug has reverse polarity relative to the laptop. - the inlet for the laptop is very small. so i took a diff adapter and sliced and joined with a small pin. the adapter had red and white wires and pin had red and black wires. joined black and white, red and red. i guess the outer portion is negative and the inner portion positive for the pin. \$\endgroup\$ – arjun Aug 29 '14 at 12:17
  • \$\begingroup\$ i tried to use the adapter this morning, and somehow it started working again. but i guess it will happen again \$\endgroup\$ – arjun Aug 29 '14 at 12:19
  • \$\begingroup\$ I found a funny behavior with my adapter. If the laptop is off and I connect it, it starts charging. But if I turn on the laptop first and then connect the charger, it wont charge. I have to first turn it off, connect and then turn on laptop. \$\endgroup\$ – arjun Sep 14 '14 at 11:15

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