Posted on by selcukozbayraktar

DC Power Supply using a notebook adapter

A GOOD DC POWER SUPPLY USING A SCRAP NOTE BOOK CHARGER

DC Power supply is an indispensable part of any design. Notebook adapters are cheap, of good quality, compact and with output power ratings around 80W. You can even find several of them in the hidden corners of the house, scrapped from old notebooks. It would be great if I could use them for my designs. But unfortunately they have weird output voltages like 16V, 22V etc. whereas I need 5V, 9V and 12V.

I opened some of them to look if there is any chance to change their output voltages, but nope. They are all optimized for their design output and compacted into a tight package.

KEEP AWAY FROM TERRIBLY BAD PERFORMING POWER SUPPLIES

Other alternatives are cheap DC Power Supplies that can be purchased from the shop at the corner, like this one below:

It is a 10A 5V DC Power supply with nice specs on the paper. But when I attempted to use it to drive stepper motors of my CNC, funny things happened. My CNC either fainted or became crazy. Finally I decided to check supply voltage with an oscilloscope.

And bingo ! I found out following picture:

These spikes that reach to +- 7-10 Volts can not be detected with a multimeter. This power supply is radiating parasitics to the connected devices and into the air !

I don’t mean all of them are bad, but this is a warning so that each of them should be checked carefully before connecting them to your circuit.

MY APPROACH TO OBTAIN A GOOD DC POWER SUPPLY

So I decided to find a way to use notebook adapters in my projects, whenever I need lots of amperes, such as driving stepper motors.

NoteBook adapter

Advantages of this approach:

  • These power supplies are well designed and tested. Their CE marking is serious.
  • They are compact, well sealed (IP 55 and mostly better)
  • They are powerful, they typically deliver 3 to 5 Amps, over their rate voltage. (50-100W)
  • They are cheap due to high volumes, you do not need to buy them, you can find scrapped ones every where. Look around your home, friends homes and work place.

HOW TO OBTAIN HIGHER OUTPUT CURRENTS USING CHEAP DOWN CONVERTERS

So, we come to solve the problem of output voltage. I tried successfully following switched mode step down converters.

2596 based DC/DC converters. Adjustable on top, the one with fixed output at bottom.

These are very cheap devices that can be found on Ebay, Aliexpress and Bang good. But this case we have another problem. These modules are based on popular 2596 chips that can only delver 15W with heat sinks. To overcome this  barrier, I split my load in smaller parts so that each of them does not exceed this limit.

In my case my CNC controller drives 3 stepper motors, and now, each of them can be separately fed from the same notebook power adapter.

Three down converters on a heatsink to drive 3 stepper motors

Above: Three down converters mounted on a heatsink to drive three 3A stepper motors. Main 19V power supply can be seen the white one on right.

I connected three adjustable downconverters at the output of Notebook Power supply. And each converter supplies one of the stepper motors happily.