Completed Project Can I modify the output voltage of a laptop adapter from 18.5V to say 7V or 13.6V or variable o/p?

Thread Starter

Rahulk70

Joined Dec 16, 2016
498
I have an old 18.6V 6.5A adapter from an old HP docking station. I tried to open the adapter and saw an small pot inside it, tried turning it but the out just remained constant and there was no change. How can I change the output with minimal components. I had previously tried with an LM2596 Buck converter to step down the voltage unfortunately I accidentally shorted the leads and it blew up. So, my first option would be to get a similar buck conv with a 75W or 100W capability(around 5A) or I need to get the above mentioned fixed voltage or a variable one by adding say a pot? Also is it safe? I've seen people mentioning its dangerous trying to modify ATX PSUs.
 

takao21203

Joined Apr 28, 2012
3,695
yes its good advice to use ready made module its a hassle to build these yourself I did for some while but when I just need voltage converter theres no need to invest an hour or two.

Modifying of course is possible you have to find the feedback path you end up with reduced current capability but its certainly possible with most switching supplies. I wouldnt recommend modify ATX power supply the PCB traces are as such you will find it difficult to replace parts and the whole thing still working relieably and there are unexpected deviations of the circuits employed compared what you can find on wikipedia.

Moreover these are designed for symmetric loading so if you only load one channel you may find the voltages sagging or the whole thing blowing up in the worst case. Low currents (i.e. not on full power) are no issue.

I have used laptop brick for a LCD flat panel the original adapter was missing so I used a small ready made buck converter.
 

Thread Starter

Rahulk70

Joined Dec 16, 2016
498
yes its good advice to use ready made module its a hassle to build these yourself I did for some while but when I just need voltage converter theres no need to invest an hour or two.

Modifying of course is possible you have to find the feedback path you end up with reduced current capability but its certainly possible with most switching supplies. I wouldnt recommend modify ATX power supply the PCB traces are as such you will find it difficult to replace parts and the whole thing still working relieably and there are unexpected deviations of the circuits employed compared what you can find on wikipedia.

Moreover these are designed for symmetric loading so if you only load one channel you may find the voltages sagging or the whole thing blowing up in the worst case. Low currents (i.e. not on full power) are no issue.

I have used laptop brick for a LCD flat panel the original adapter was missing so I used a small ready made buck converter.
Thanks. So, I guess its safer to go with ready made modules.Which is the best buck converer for getting the max current from this laptop adapter (6.5A max). Do you think XL4005 or 4015 will be a better choice? Most of the high wattage (300W) ones are usually boost converter I saw on ebay or amazon. Do you know any good buck converters with higher power capability?
 

Dodgydave

Joined Jun 22, 2012
9,072
Any atx or laptop psu can be made variable or modified to give a different voltage output, the easiest way is to remove the opto-coupler as this makes it give out full voltage, then using a ready-made buck converter chip like LM2596, on the output to make your own Variable voltage.
If you choose this method, increase the Voltage rating of the output capacitors on the atx/laptop.

Otherwise your looking at altering the feedback loop to the opto-coupler to achieve a variable voltage.
 

Thread Starter

Rahulk70

Joined Dec 16, 2016
498
Any atx or laptop psu can be made variable or modified to give a different voltage output, the easiest way is to remove the opto-coupler as this makes it give out full voltage, then using a ready-made buck converter chip like LM2596, on the output to make your own Variable voltage.
If you choose this method, increase the Voltage rating of the output capacitors on the atx/laptop.

Otherwise your looking at altering the feedback loop to the opto-coupler to achieve a variable voltage.
I've used an LM2596 in the past and accidently shorted its leads and the IC immediately blew up. Moreover I need a converter that can handle more current.Was planning on an XL4015 or XL4005. Do you happen to know the difference between them? they looked almost identical to me in specs.
 

Baelin QC

Joined Mar 30, 2020
1
I have an old 18.6V 6.5A adapter from an old HP docking station. I tried to open the adapter and saw an small pot inside it, tried turning it but the out just remained constant and there was no change. How can I change the output with minimal components. I had previously tried with an LM2596 Buck converter to step down the voltage unfortunately I accidentally shorted the leads and it blew up. So, my first option would be to get a similar buck conv with a 75W or 100W capability(around 5A) or I need to get the above mentioned fixed voltage or a variable one by adding say a pot? Also is it safe? I've seen people mentioning its dangerous trying to modify ATX PSUs.
If you are trained to know what you are doing then ATX conversion is simple as i made one as 1st class project for multiple voltages to have available at same time to supply multiple circuits, but stay safe and when unsure inform yourself with qualified help
 

Thread Starter

Rahulk70

Joined Dec 16, 2016
498
If you are trained to know what you are doing then ATX conversion is simple as i made one as 1st class project for multiple voltages to have available at same time to supply multiple circuits, but stay safe and when unsure inform yourself with qualified help
I'm aware about the high voltage risks associated inside an ATX PSU. I do work with vintage tube related electronics so I'm quite used to working around high voltages and comfortable with it. But in the end I got one of those High wattage boost DC-DC converters and made a power supply. It was mainly to charge some 6V & 12V Lead Acid SLA batteries I had.
 
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