Friday, October 17, 2014

20 Volt DC Expansion

Now that we have covered 5 and 12 volt DC power applications over USB and Ethernet, this post will be about 20 volt DC expansion. This voltage is very common for laptops and Chromebooks/Chromeboxes. It is important to note that some name-brand manufacturers will have a third 'sense' wire in the power cable, to ensure that a no-name or incorrect wattage power supply is not used with their systems.

A good example is my Dell Precision 6500, which has a comparatively large (and more expensive) power supply for a standard-sized laptop/dock. A more-common Dell laptop power supply has the same plug, but I am warned that the wattage is not sufficient if I use anything other than the 210 watt unit that is designed for it. At 20 volts, that wattage means more than 10 amps of current, a phenomenal amount that I do not have the answer as to why the laptop needs so much (the battery, with nice LED level indicators, has always lasted me about two hours of use away from the dock).

I have an extra supply, that had its cord cut by my boss of the time, thinking that the unit was bad. As you've learned by now, I then think of ways to put it back into use. You should also know that I have too much of my Dad's blood in me, and that we never thrown an item away in the hope that we can fix it later.

My ASUS Chromebox in the office is also 20 volts DC, a power supply that is half as large. It has a very-common 5.5mm x 2.5mm (the same dimensions of the power plug for older Roku units) plug for power, without any 'sense' line. In addition my Lenovo 11e Chromebook and my wife's Lenovo convertible laptop/tablet also have 20VDC power supplies, a fifth of the size of that of my Precision. I have an adapter plugs set that I should have covered in earlier posting, in that they have the common 5.5mm x 2.1mm jack inputs, and convert it into all of the plugs I will use on this project.

Here are the pictures:


  1. The first picture is beginning the project, the second shows the Dell cable I am using to restore the original functionality. The third picture is various connections I have to more easily test the voltages from the barrel connections on the cables. In the third picture you see the dock power supply, twice as large as the "portable" power supply (which is still only a third of the size of my closed Lenovo 11e Chromebook. The fifth picture shows the plug adapters, I am able to adapt to the ASUS Chromebox, Lenovo plug, or what Dell uses (without the 'sense' wire). The last picture is the finished power supply.

  2. I do recommend having a good voltmeter, and checking your work a few times for correct polarity and the absence of shorts.

  3. Note that I did make sure the new cable can supply enough power for my Precision dock. The larger supply is rated as 19.5VDC at 10.8 amps. For the smaller supply I repaired, it is rated as 19.5VDC at 12.3 amps. That provides at least 1.5 amps more leeway, and I am certain the current draw of the Precision in the dock, and the additional power for my ASUS Chromebox will easily be below the rating of the repaired power supply.

  4. My adapters for the power connections that Lenovo uses came in today. The voltage/ammeters are still in-transit. I'm going to do voltage and current draw tests as I go through having everything powered on together.