I had to finish the work and needed some power source. Luckily I had a Dell power supply, but unfortuantely the dc jacks where different.
Having a look at the power supplies I found out that they are very close in specification.
Lenovo (DCWP CM-2 135W);
- 20V DC
- 19.5V DC
I thought that the 0.5V and the 5W difference of the power supplies should not be a problem ... but the dimension of the power jacks where. The Dell jack did not fit into the Lenovo socket.
While you work on such power supplies, even if this is low voltage dc, there is high current. Shortening the dc jack may lead to demage of the power supply and can even cause fire because of generating heat. Be careful, double check every step. Be as much precise as possible.
Step 1: Comparing the Power Supplies
The voltage is nearly the same. Also the power that both power supplies are able to spend is nearly the same. Polarity of the pins is also the same.
When looking for the connector type of both power supplies I was not able to find a standard describing them. It seems to me that Dell and Lenovo are using their own connector design.
Step 2: Connector Construction
http://en.wikipedia.org/wiki/Coaxial_power_connector . The standard mentioned here does not support the high current and the relatively high dc voltage that Lenovo uses (see also http://en.wikipedia.org/wiki/EIAJ_connector ).
The plug is built by two metal tubes that are separated by insulation matterial. The pipes offer big surface to conduct. There is a small pin in the center of the jack. I think that this pin has no meaning for the electrical functinality of the connection. I think it is just a guiding pin with no electrical connection.
The socket is mainly built out of plastics, to support the jack. Inside the socket there are small clips that conduct to the tubes when the jack is plugged in. There are two clips for each tube to offer the best conduction possible. One pair of clips conduct to the inner tube the other pair to the outer tube.
Step 3: Modifying the Dell Power Supplies Jack
I made small slit into the jack's tubes. This way they became somehow flexible like a strong spring.
To cut the slit I used a Dremel tool. The slit need to be cut all the way down the tubing. It need to end some millimeters inside the base of the jack. Be careful not to cut the guiding pin.
After cutting the slit needs to be cleaned somehow. Some chips may be left from the cutting. They should be removed with sanding paper. I used type 180 and type 240 paper.
Check the slit carefully for any defects and chips after sanding it.
Step 4: Usage
Do not twist the jack while plugging it in or when it is plugged. The slit inside the tubes may scrape of some plastic of the socket of the notebook.
The modified jack is still useable in Dell notebooks too.
I used the Dell power supply for a whole working day to finish my work without problems. I am using it from time to time at a customer site, leaving it there and using my original power supply at home.
You should always be aware of the fact that you are dealing with high current here. Leaving chips inside the jack may lead to short circuit and may destroy the power supply. The current may be able to burn of chips but may cause fire by doing so. If you notice a strong smell or unusal heat on the connector turn it off immediately.