# Supply voltage drops AFTER connecting to device [closed]

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?

## closed as off-topic by Leon Heller, JYelton, Chetan Bhargava, Daniel Grillo, Matt YoungAug 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
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• Is the plug polarity correct? (What happens to the voltage of the computer?) – George Herold Aug 28 '14 at 19:53
• 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. – arjun Aug 29 '14 at 12:16

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.

• 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. – Matt B. Aug 28 '14 at 20:15
• I like the reset-able poly fuse idea. – George Herold Aug 29 '14 at 2:00
• 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. – arjun Aug 29 '14 at 12:17
• i tried to use the adapter this morning, and somehow it started working again. but i guess it will happen again – arjun Aug 29 '14 at 12:19
• 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. – arjun Sep 14 '14 at 11:15