How to Build a Laptop Adapter Tester for 20V 90W With Voltage and Load Current Display

I'm trying to test a bunch of laptops adapters that are supposedly not working. I have done quite a lot with multimeters and probes but is there any device that would just allow me to plug the adapter and read output voltage and current without and with a load? Or if I have to build it what would be the best way to go about it? Normally laptop adapters go up to 20 V and 90 W max.

Hi Steve

Use a light bulb or build a resistor load Using Ohms law equivalent to 90w or what ever the output power is. That’s how we used to test switch mode power supplies on TV's same way

A couple of car halogen headlight bulbs connected in series would suffice in certain instances

P = V x I or P = I^2 x R or P= V^2 / R.
I = P / V or I = (P / R)2
V = (P x R)2 or V = P/ I
R = V2 /P or R =P / I^2

using above equations to solve for R (Your dummy Load )

You want the load to be just under specified output power otherwise the over current protection will kick in if you exceed maximum load but you can normally tell as you will hear "Click, Click, Click " Of the swps “Switch mode power supply” as it trips due to either over current or over voltage

See this page if stuck
http://www.electronics-tutorials.ws/dccircuits/dcp_2.html

Hope this helps

MD Harrington

www.harrington.force9.co.uk

If you are stuck for a calculator I’ve attached Derive Dos version only, but will help you to solve for V , I or P and then you can plug in the values of what you know and calculate the unknown Wont take you too long to figure this out couple of hours or so


Runs on XP I don’t know about other windows OS You will have to try it out and see

Very good for solving other Math’s problems as well

See attached

Hope this also helps you

Mark

www,harrington.force9.co.uk