How hard would it be to build an atx power supply?

[ivwshane]

I'm sure designing a power supply is a lot harder than actually making one.

But after playing with a couple of ATX power supplies and looking at their interiors I don't see anything that would look to overly complicated.
If someone has decent soldering skills, how hard could it be?


The reason I ask is because quality power supplies have sky rocketed in price over the past couple years and even high priced ones don't guarantee quality. And I've also been accumulating spare psu from old computers I'm looking to put them to good use.

Based off of what I have read a good ATX power supply has three maybe four characteristics:

Efficiency
stability
high output on the 3 and 5v lines

and maybe quietness.

Given those requirements what dictates those characteristics in a power supply (besides design, which I know plays a big role)?

 

[f95toli]

The problems is that designing a good switching power supply is very difficult, it is much more complicated than designing "classical" power supply using recitifers and big capacitors.
Unless you have a good knowledge about high-frequency analog design and access to the right software (for simulations) I doubt you could build something that was BETTER than a commercial design.

 

[Navid]

Originally posted by: ivwshane
Based off of what I have read a good ATX power supply has three maybe four characteristics:

Efficiency
stability
high output on the 3 and 5v lines

and maybe quietness.

Given those requirements what dictates those characteristics in a power supply (besides design, which I know plays a big role)?

There are trade-offs between those requirements. For example, it is not easy to keep it quiet at low efficiency. It is not easy to increase the output power and keep it efficient at the same time.

Another matter for the manufacturer's to struggle with (which is your only advantage) is manufacturability. They need to keep their yields high while keeping their production costs low. They need to make money after all or they will go out of business. So, they have to make some compromises on all those requirements you listed in order to lower their costs and raise their yields.

You, on the other hand, can spend a lot of time and hand pick components and tweak everything to optimize everything to what you desire. So, yes you can do it and make a good power supply for yourself. But, going into business and running a company that makes and sells power supplies is a different story!

 

[ivwshane]

So what components of an atx ps can I modify to make it better? Or is that even a possibility? Would replacing the capacitors with lower impedance do anything?

 

[sjwaste]

Sounds like it's an issue of what your time is really worth (unless you just want to do this for fun, I don't put a price tag on time spent doing that). I mean, if you're going to spend 12 hrs researching, another 8 to build, even if your time is only worth 10 bucks an hr you don't come out on top. I'm sure a $2-300 PS can have some guarantees on quality.

 

[Navid]

One popular mod is to quiet down a noisy power supply.

Keep in mind that a problem with a power supply can cost you a lot! A power supply that goes bust and over-volts can damage many of your computer components.

So, I strongly advise against modifying a power supply unless you are aware of all the risks (not to mention safety risks) and are OK with them.

 

[ivwshane]

Yeah I'm aware and completely ok with the risks.

I have lot's of spare computer parts to sacrifice

 

[Mark R]

To be honest, there isn't much you can tweak without breaking something.

Easiest things to mod are fans - replace the stock fans for quiet, low speed fans, you'll have to reduce the maximum rating of the PSU to stop it burning though

Other moddable things are:
Input reservoir capacitors - bigger caps mean more energy in reserve if the mains power drops out. ATX PSUs must keep a 0.016 s reserve at full load - double the size of the caps, and limit your PSU to one-third power, and you've now got 0.1 s of reserve (that's potentially useful). But, too big and you risk burning the mains filter/rectifiers.

Limited tweaking of the output voltages:
Most older ATX PSUs don't individually regulate all 3 main rails - they tend only to regulate the 3.3V independently, with the 5V and 12V coming off the same regulator. Adjusting the various voltage dividers should enable you to tweak the voltage rails slightly (though don't expect the PSU to work well, if you make big changes). You won't be able to change the 5V/12V ratio (that's fixed by transformer turns ratio, and won't be tweakable).

You can change the output filter caps if you want, but can't imagine that you'll do anything useful. They'll already be low impedance, going for ultra-low impedance is unlikely to improve performance unless you also adjust the feedback loop compensation. Feedback loop design is not easy, and it's essential that it's done right otherwise the PSU won't work properly (potentially resulting in damage to the PSU).

Make sure you are fully competant working with mains voltage equipment. Remember that the input reservoir caps charge to over 300V (over 350 V in an active PFC PSU).

Tweaking pretty much anything else is going to be impractical. Power rating, efficiency, etc. all highly dependent on the PSU design and specifications of the parts - often in a complex way. E.g. replacing the regulator transistors with more powerful, lower resistance ones, could actually worsen efficiency (because of their lower gain/higher gate charge).

The transformers in the PSU will almost certainly be custom made for that specific design, so you won't be able to 'mix and match'.

 

[ivwshane]

Thanks, that's the kind of info I was looking for.

So the answer to my question seems to be no, there isn't anything definitive that you could modify on a powersupply to improve it's quality.


That's too bad, I was hoping to start playing around

 

[Jeff7]

Power supply companies have thousands of dollars to spend on R&D, while paying professional engineers to design these things. No offense, but based on your questions, I'd say that you have neither.

If you want to have fun with some dangerous electricity, build yourself a small Tesla Coil. I built one that produces around 75-100KV for less than $100.

 

[ivwshane]

Which is why I asked questions

 

[dkozloski]

One avenue you don't see explored much is to build a power supply that is outside the case and remote. You can build it as large, noisey, and hot as you like but it is now a simple matter to shield yourself and the computer from these elements. Think outside the box(case) so to speak.

 

[maluckey]

I re-capped a dead PSU and am still using it three years later. The original died in six months. I didn't change the design, just the caps though. I decided to use Black Gate of similar ratings since I had lots left over after toying with my stereo amp project.

I went slightly larger on the input, and used several smaller caps in parallel on the output side, but of similar value in total. I'm not sure it would be worth the cost if the caps weren't seriously discounted. The performance is good, and it runs at higher temps than before without a problem.

 

[trend]

I wouldn't really change out the caps on a PSU (to lower, high capacity)... adding some nice size caps could help you turn your psu into a 'smart' psu (smart taken from 'smart' ups... a smart ups being a ups that adds large caps to clean out the nasty ac in).

heh, i am just talking crazy like... really tired, but cannot go to sleep :/

 

[dwcal]

This might sound obvious, but one possible mod is to install better heatsinks. This goes well with a fan mod to reduce noise, and more cooling is always good.

 

[maluckey]

You could set up a cascade on the input side to clean A/C noise. Wouldn't be too hard, though likely not worth the $$$ as a good Sparkle PSU unit is less than a hundred bucks.

The issue is than PSU's are soooo cheap that to make it worth your while you would have to do something radical, like a UPS/Line Conditioner/Silent/Neon Lights and a coffee maker PSU with enough juice for a TEC Watercooler setup to run off of it.

 

[ding5550123]

I am sure you have to get your hands on a really good transformer. That's all i know about PSU's. Considering i've never opened one


I don't even know so don't listen to me

 

[ivwshane]

Originally posted by: maluckey
You could set up a cascade on the input side to clean A/C noise. Wouldn't be too hard, though likely not worth the $$$ as a good Sparkle PSU unit is less than a hundred bucks.

The issue is than PSU's are soooo cheap that to make it worth your while you would have to do something radical, like a UPS/Line Conditioner/Silent/Neon Lights and a coffee maker PSU with enough juice for a TEC Watercooler setup to run off of it.

Have you seen the prices recently? They keep going up for no good reason!!

Fotronsource makes some pretty inexpsensive power supplies that out perform more expensive ones, yet "high end" high priced power supplies continue to come out:|

 

[Future Shock]

PSUs expensive? Well, considering what a PC Power and Cooling supply has always cost, I don't think that they have gone up. But there is more competition in the higher end, no doubt, so the average price probably looks higher.

Frankly, I used to use all PC P&C Silencer units, for well over a $100 each (and this goes back a few years). But today's supplies are so good that my main PC is powered off the Antec PSU that came with my $90 Antec Aria case.

The problem, IMHO, is that the PSU industry has really oversold the need for VERY large, high capacity PSUs. Everybody and their brother now thinks they need 500W PSUs, and they also need to have lights, and they also need to be really quiet. OK, I agree on the last item, but I am pushing a fairly decent PC (see sig) with the 300W supply that came with the Aria. Unless you are running a server with 5 harddrives, dual CPUs, etc. or a gaming system with SLI and overclocking, you probably don't NEED 500W. But those higher wattage units sell very well, and for very high prices...

Future Shock

 

[dkozloski]

It's all part of the macho based "who has the biggest one?" peeing contest.

 

[Witchfire]

I've modded more than a couple of PSU's in the past, but that was always for vmods. As far as improving quality... well, you could go through any/all caps & resistors & replace w/ ones of the same value but tighter tolerances (i.e.- replacing all 5% resistors w/ 1% variants), but as was said previously, you'll spend more doing it yourself than you ever will buying a quality PSU in the first place. Took me half of forever to figure that out.. all it took was plugging in my PC Power & Cooling 510 SLI for the first time & looking at the Health Stats in my BIOS... ROCK SOLID!!! None of the rails vary a BIT. My vmodded Antec 550 was good, but it never got readings that solid.

Now the part about building your own? Given enough time, research, trial & error, Yeah, you could do it, and maybe even make one as stable as a PC P&C model, maybe even more powerful. But managing to cram it all in the space occupied by a PSU would be murder.

I agree with Future Shock about the industry getting wrapped up in wattage wars. Most people will never need a TRUE 500 watt PSU, it's just the whole ePenis thing. Hell, I imagine most are just slapping different stickers on existing units that state higher ratings. Most manufacturers rate their PSU's at 25 degrees Celsius, which will NEVER happen. 40 or 50 is a better bet. the typical '550' watt PSU is actually little better than 300 wats at those temps. I definately see a need for a universal rating system, until that happens, all ratings are arbitrary.