How do PSU's work?

FIRST A WARNING!!
As I think Britton30 pointed out any tampering, dismantling, or attempts at repairing these units is potentially fatal as referenced in Brinks post on a teen death. From personal experience I can say that during my uninformed years I have by sheer accident breached some of the terminals while taking these devices apart and have witnessed the destruction of the item that came into contact with the stored energy with the capacitors in thee units.
I might add that this applies to anyone dismantling microwave ovens, old TV sets or ANY device that uses capacitors in any size - even the small ones can BITE - you must treat all capacitors as charged - to ignore this warning is foolhardy and as stated potentially fatal.
Working as an RN I can attest to the power of these electrical components in that they are the actuating "item" / component in a defibrillator machine. Now we have all seen how those things work (or supposedly work - dramatised for viewers) on TV or films but in reality it does stop the heart!

However:-


Seeing there is a debate within the tutorial on PSU's I felt it necessary to start a new thread for any discussion or debate that isn't strictly general information on PSU's for average user.

So given that I do have a fairly limited and self taught knowledge in that I do know that high currents that are needed within a computer can be supplied by a rectified voltage source form a mains transformer.

However to supply the currents that we now need by purely using a dedicated transformer/s requires huge, heavy, and VERY expensive transformers, therefore it takes some very clever switched mode circuitry to be able to use smaller and therefore cheaper transformers to produce the currents that are required.

I did some researching and came up with this ref and some very interesting videos should anyone want to see what goes on in a PSU.

Switching-power-supply « « Electronic Circuits diagrams Schematics Projects*:: Next.gr

AGAIN - WARNING!!
Any tampering, dismantling, or attempts at repairing these units is potentially fatal!!

Or as the labels say, "No user serviceable parts inside". Aside from the very real electrocution hazard capacitors can and do explode. Some have a semi-liquid electrolyte and other components which will be very hot and stick to and severely burn you. There can also be shrapnel which can take an eye out and cause deep cuts in skin.

Britton30 said:

Or as the labels say, "No user serviceable parts inside". Aside from the very real electrocution hazard capacitors can and do explode. Some have a semi-liquid electrolyte and other components which will be very hot and stick to and severely burn you. There can also be shrapnel which can take an eye out and cause deep cuts in skin.

Yes I know from my old audio building days I blew a particular vacuum tube amplifier to bits when the two main ripple caps exploded showering me with and the room with snow like debris - the electrolyte you speak of really burns not only from heat but the chemical reaction on your skin.
This was caused for sake of interest by the caps being hooked up in reverse polarity by mistake. Experiments showed me after even small ones can and do explode with some violence. Those old electro's were just really a swiss roll of two thin metal plates separated by a tiny gap with electrolyte in between.
What would happen with the new ones I don't know and am not about to try LOL!!

Nice thread John, hope this discussion on PSUs continues, I find this very interesting.

Let me know if you want any of the posts from the PSU tutorial moved here.

Well Dave I was hoping westom would see the thread and come over as I find this stuff rather fascinating.

But I do think that some debate and or discussion is pretty relevant given that a lot of us do tinker with these devices and as I said it is not limited to PSU's. I took to taking out those super magnets from microwave oven's magnetrons and they have some REALLY substantial caps in them (not to mention the toxic beryllium cylinder that holds them apart) and I was unaware of the danger until much later. By the way those magnets are the ones I use stuck onto plastic pots for holding screws etc if you wondered why I was getting them.
Instead I use the super magnets out of old hard drives now and some I had for prospecting - bit safer LOL!!

I did find some caps once from an industrial main frame computer at the local dump and they had a capacities of between 1 -4 Farads not micro farads but whole ones and at some unholy voltage ratings if they had been charged when I and my son were handing them I wouldn't be sitting here typing now

if you are curious about how PSU look inside but don't want to die young, you can easily head for PSU review sites and find a ton of pics and differences between good and crappy ones, with decent explanations on what you are looking at.

They open most PSUs for the sake of it. for crappy ones you see even pictures after they failed in their 100% load tests.

This could be added to the tutorial maybe, just to satiate curious people.

As for powering stuff, I successfully used external 5V power supplies to power most HDDs and DVD drives, but for the rig and especially the graphic cards I don't think it is wise to even try. Too rapidly-shifting loads, anything not specifically designed to do it is likely to fail.

Indianatone said:

Britton30 I read your tutorial and thought it was excellent, everything we need to know. There will always be those who know more and start to go overboard but since I left work I no longer have a scope just a couple of digital voltmeters.
One suggestion to admins IMHO if you have allowed a tutorial to be created for reference purposes could it not be locked so we don't get them spoiled by people writing a ton of replies of you should do this or you should do that?

Well Indie I am glad you picked up on that and that you have some in depth knowledge I think locking the tutorial could be done but only for openly critcising the tut.
I ran some things past Gary first as I thought they were important legal if not pertinent PSU tech specs and they were basically aimed at covering his six in these days of legalistic wrangling. I didn't go in like I guess some would and spoil it just to be a pain in the neck.

I did some testing on some old PSU's I have here that I will not elaborate on my methods because you can bet your sweet life that some fool will try what I did and well you know what can happen.

Now before I go any further I have to say I did these tests at my own risk and I am NOT inferring that anyone does their own tests unless they are a qualified technician. As Indiantone has already said these devices should never be touched apart from a qualified person.

I for one would like a simple, understandable of how switched mode circuitry works and what it is/does. I have looked at Wikipedia and electronic sites and have a headache from seeing squiggly lines and diagrams.

The same paper clip test is listed on the Corsair site with no warnings or other unneeded info.