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Hi, I am trying to upgrade a computer Power Suply to provide from 20amp to 30/40 amps. I was checking the transistor (NEC-K2485) on one of the Power Suply, that I guess I have to change in order tu burst the amperaje. I was looking thgroug the internet, but get lost in the process. Can anybody point me in the right transistor. Again I want to increase amperage from 20----->to30/40, thankz

Just buy a higher current PSU.

Your unspecified Power Supply Unit (PSU) is almost certainly a switch mode PSU (SMPS).

Upgrading an SMPS is far more complex than just beefing up the switching transistor.

:)

Hi, thanks for answer, now, I dont understand the (unspecified), what shoul I specify on a COMPUTER power suply, do you know the box inside a regular PC (computer that provide power to the whole system (mother board,hard drive, etc, etc. , well let my try to understand, here, should I mention all the electronics components inside, like the transformer, big capacitors, etc, etc, kind crazy, eh, well this Power suply most of them, provide voltages 3.5, 5.2, 12.2 at aprox 20Amp, thats the most important feature on them, now. If you check my question, I speify the most important TRANSISTOR on most of them, (it changed depending on the branda and Wats) but basicly the same specs. Thisone apparently is the magic one that turn the electricity to 20amps. Finnally, I am a NUB, and I dont know a lot about electronics, and if I am trying to do this is becouse I dont have enought resorces to buy a higher current PS. A frien of my toll me that changing this transistor, will do the work, He fail on getting me the right transistor reference. So, again I am looking for somebody who could helpme taking the time to analize my question and point me in the right direction to do the change. Anyway, thankz again for your imput.

I used the term "unspecified" because you did not give a part number or generic type (linear / switched mode) for your PSU.

You would be wasting your time drawing the internal circuit diagram and trying to find all the part numbers of a commercial PSU.

Uprating such a PSU is much, much more than fitting a higher current transistor.

Just because other apparently similar but higher output PSU's have a different transistor, you cannot assume that is the only thing that is different.

You have to change several of the capacitors, several of the inductors - one of which will be a safety rated high frequency flyback type of isolation transformer - probably MOSFET driver IC's and hardest of all you will have to redesign the frequency compensation to ensure the PSU is stable with the new transformer and inductances.

If you were an experienced PSU designer, you just might consider buying the bits for a suitable design based on the PC PSU specs and semiconductor manufacturers applications notes but unless you were going to make thousands you would probably spend too much in R& D.

I'm sorry but as a newbie to electronics this project is not for you.

Just buy a higher current PSU off ebay or Amazon or the like.

Your other option is to think very hard about why you think you need another 10 to 20 Amps and then think of ways to avoid it.

Hi, again, and thankz for the time to explain me what was going on, and in fact I fell so dumb now that you explainned to me, cz indeed, and that confirmed my initial concern when my friend toll me it was just a quick unsoldering and soldering of a 3 pins Mosfet. I was so amaze that he said that I couldnt beleive it, but I beleive it, so thats why. Now since this is really a dumb idea, I still need a Power Suply that provide-5.5/12V at 30/40, see is for Radio Control, and I am experimenting with brushless mottors and Speed Controllers, they certainlly work at 20amp but not enouhg current for reaal lifting, as you know this kind of mottor are designed to perform at that range of amperage, I have a Lipo Battery that I am using, but every charge only last 15 minutes, their nice for flying, not for testing, and I am alway afraid that is gonna catch fre or explode... Anyway, Im gonna stop the looking for a Transistor, and star looking for a Power Suply, but, what exactlu should I look, would you pelase point me, I wont botter no more after this. Thankz again.!!! Oh BTW I have buld TRICOPTER, I have expend so much money and time on it that I am abaut to give up, It is not flying as it is so hard to set up, (Radio, Control board...but, since I am a Mental person (Depression/ansiety disorder), this is a good therapy to keep me bussy. Thankz again.

@Sancho_P, @arduinohacker, @CarlSawtell,

Anyone on CL know about how to connect up PC PSU's to use as a bench supply?

Try googling for:

how to use a PC PSU as a bench supply

or

how to convert a PC ATX PSU to a bench supply

or similar search terms.

Here's on example of stuff that turns up this way:

http://www.wikihow.com/Convert-a-Computer-ATX-Power-Supply-to-a-Lab-Power-Supply

Beware: PSU's run from mains voltages. Internal capacitors may store voltages capable of delivering a lethal shock long after the unit has been disconnected from the mains.

Unless you are absolutely sure of what you are doing, do not attempt to modify any such unit.

Thhankz so much!, btw, I wont touch those capactors..:)

Be very cautious to misuse such power supplies:

The high voltage cap (primary side) is a killer.

The unit needs a minimum load to control voltage, may not work w/o load.

The rated power assumes an average load on all outputs.

They are short circuit protected, but 30A (or even 12A) are a very high current in electronics …

For testing strong 12V DC motors I’d prefer an old car battery (and simple charger), but take care:

• 200A are a really high current …

Regards, Sancho