Be carefull! (another sight on power supply issue)

[Ruslan]

I've seen so many questions like "what Power supply should I use - 250w or 300w?", so in the end I decided to post my own opinion on that question.

Few days ago I saw assembled PC by one well-known PC brand company with followed spec:
Chaintech microATX socket A MoBo(don't know exactly model,though)
Thunderbird 700 with ordinary cooler
ATI 128PRO AGP board
128Mb PC133 DIMM
7200 Fujitsu HDD
Sony CDRW 40x
rest- standard equipment except for ... case!
I really was tempted to see pretty good Daewoo microATX brand case with ... guess what - 112w(!?!)power supply! Unbelievable, but system worked stable as rock!

I have already knew, what Duron systems (and I made same ones,BTW)can work stable with 250W power supply,... but 112w!!??... This triggered me to post that topic...

My father-in-low working as repair tech and
now specialize in repairing power supplies.
Here some tips,what we found togever with him recently...

Have You ever noticed, what THE REAL DIFFERENCE beetwen 200,230,250 or 300watt PSU? No? Why one system works perfect with 250W,while didn't work with 300w?

The real difference beetwen Power supplies
(lets assuming,ATX ones and from same manufacturer) are types of powerfull high voltage and MOSFET transistors and types of diodes Shottky, used for output voltage channels. And also high-voltage capasitors,used for invertor.

I've seen some "250w" PSU, what couldn't provide even 120w without overheating.
Followed comparison table(statistic data)can help You to identify Your power supply REAL POWER.
---------------------------------------------
200watt power supply:
---------------------------------------------
1.High-voltage capacitors - 2pcs x 220Mkf,200v
2.Inverter transistor type - 2x 2SC2335 or similar, 500v,4a, 40-55w heat dissipation
3.Output diodes - 1x20a,30v 2-in-1 shottky diode (for +12v output power)
1x20a,30v 2-in-1 case TO-220
Shottky diode for +5v output
4.MOSFET power transistor - IRFZ34,2SK1388 or similar - for +3,3v output. 30-40V,29Amp
---------------------------------------------
230w:
---------------------------------------------
1. 2x 330Mkf,200v
2. 2x 2SE13007 or similar - 500v,5A,60w
3. 1x 20a,30V 2-in-1 plus 1x 30A,30V 2-in-1 Diode
4. 1x IRFZ44N or similar - 40A,55V
---------------------------------------------
250W:
---------------------------------------------
1. 2x 470 or 680Mkf,200V
2. 2x 2SE13007 or more powerfull transistors - 500v,5A,65W
3. 2x 30V,30A 2-in-1 shottky diodes.
4. 1x IRFZ48N or similar - 45A,55V
---------------------------------------------
300W:
---------------------------------------------
1. 2x 680 or 1000Mkf,200V
2. 2x 2SC2625 - 500V,10A,100W
3. 2x 40A,30V 2-in-1 Shottky Diodes
4. 1x 65A or above ,55V power MOSFET transistor.
---------------------------------------------
Rest of components usually same for all types of PSUs.

Output power also depends from size of all heatsinks. If You've got PSU with very small heatsinks, You'll get big problems in future.
Powerfull transistor for standby mode (2SC5027 or similar, 1000v,3A) should have own or at least shared heatsink - this help You to avoid futher problems (I've seen so many MoBos destroyed by that piece of s^^^t!).
Another issue... Cheap PSU usually doesn't have electromagnetic filters soldered. You can see them through holes for ventilation. Go figure...

But there is another big problem... Usually all computer cases covered by warranty, so You usually cann't get inside PSU without voiding warranty.

So,If You don't know,what inside Your PSU,
buy 300Watt power supply. At least, You'll be somehow ensured from possible headaches.

I hope, what my topic help You sort it out.
Good luck!

------------------
Ruslan Khyzha

[J741]

Usually, the issue with power supply problems is not so much the total output power capability, but the combined output capability of the +3.3V and +5V lines. These two lines are used to power the motherboard and CPU.

If you examine the "recommended power supply" list on AMD's website for the 1200MHz Thunderbird when used with an motherboard that conforms to the "ATX" specification, the combined power rating (+3.3V and +5V) ranges from 125W up to 300W, With the average semming to be around 180W-200W

So check the sticker on the outside of your power supply for the combined power rating of the +3.3 and +5V lines. If it's less than about 180W, and you have stability issues, I would consider changing it.

If your power supply's information sticker lists current instead of a power rating remember the formula P=IV, that is power (Watts) is the Current times the Voltage. So a +3.3V line capable of outputting up to 20A would provide 66W of power, and a +5V line cabable of outputting 20A would provide 100W of power, for a combined power capability of 166W.

- James.


[This message has been edited by J741 (edited February 11, 2001).]

[NeuromancerIV]

You two make very good points here with this.
The biggest customer issue I run into regarding PSUs are people who come in to buy a Socket A board, and a Socket A CPU then want to buy our cheapest case w/PS($40.00 USD which is unstable with socket A cpu's we've noted) is explaining to them AMD's reccomendations regarding PSU's specs, We finally had to institute a policy of only selling 2 particluar (well, regularly in stock casesthat is) cases for customers with Socket A MB/CPU's to avoid these kind of instability issues. (Yes one would hope the average customer who wants Socket A stuff, would have done some research 1st, but often in my area, this is not the case.

[Ruslan]

[quote]<font face="Verdana, Arial" size="2">Originally posted by J741:
Usually, the issue with power supply problems is not so much the total output power capability, but the combined output capability of the +3.3V and +5V lines. These two lines are used to power the motherboard and CPU.

If you examine the "recommended power supply" list on AMD's website for the 1200MHz Thunderbird when used with an motherboard that conforms to the "ATX" specification, the combined power rating (+3.3V and +5V) ranges from 125W up to 300W, With the average semming to be around 180W-200W

So check the sticker on the outside of your power supply for the combined power rating of the +3.3 and +5V lines. If it's less than about 180W, and you have stability issues, I would consider changing it.


Very good points,J741! Really, I forgot to mention this very important info...
Actually, both +5V and +3V regulators are located on same shared heatsink... So,now imagine, how that small enough heatsink can dissipate 125-250Watt of power?I think it rather will looks like little fryer
Ooohh yes,fan... But fans also have different speed of rotation, might be ball bearing or sleave bearing (respectively expensive enough one or cheep one).


If your power supply's information sticker lists current instead of a power rating remember the formula P=IV, that is power (Watts) is the Current times the Voltage. So a +3.3V line capable of outputting up to 20A would provide 66W of power, and a +5V line cabable of outputting 20A would provide 100W of power, for a combined power capability of 166W.
</font><hr></blockquote>

Saying for example, about 3,3V ,20A or 5V,30A manufacturer of electronic components usually means MAXIMUM output ratings for short period of time,for example, 1 minute. And some of noname PSU manufacturers also saying about short term MAXIMUM output rating (230,250 or 300W)Sometimes You even can see such sticker on the one side of PSU's case. But computer works for long periond of time! Brand-name manufacturers of PSUs are usually saying about CONTINIOUS maximum power output ratings. Feeling difference? I think, it's the one of main reasons,why sometimes seemed less powerfull power supplies from brandname PC works better, than seemed more powerfull (according to stickers),but from uknown manufacturer.

Fortunatly,ordinary PC doesn't consumes so much power...

Another issue... If You're suspecting, what You have PSU-related problems, check "hardware monitor" in BIOS. If You're see CPU voltage constantly changes in wide enough range - You definatly have problematic power supply! Cheap PSU usually means cheap capasitors,no EM filters,less powerfull components and so on...

And what I wanted to say in my topic - don't
let to be cheated! If it possible - go inside PSU and check all components! At least You can check some component's presence,i.e. EM filters and heatsinks through holes for ventilation before buying it.

Don't hesitate to ask me about any hardware-relayted problem, if something isn't clear for You...

May be, someone else have something to add/or correct me?

[bdunn]

This is common in lower end name brand computers. Most folks don't add that much in terms of hardware so the MFRs use the cheapest supply they can get away with that provides enough to fire up whats on board. In a fully integrated system you can figure out the exact power consumption of each device and add a little bit just in case. Nine out of ten users won't know the difference.

[AlienDyne]

Priceless advice (as always) by Ruslan!

[kato]

Wow ruslan,

you've covered it all in great detail. I just might add two very small and general rules I live by with power supplies:

1.) How much does it weigh? If it's heavy, then chances are it has the components you were mentioning and is shielded well and also has some heavier heatsinks. Almost all the light and "flimsy" PSU's I've come upon recently (250-300W) were crap and suited for only pentuimMMX and K6's despite claiming to have enough juice for Athlon's and PIII's.

2.) Stick with a good company until they prove your loyalty is misguided. I've found enermax supplies to be great, and I reccomend them as much as I can. I know they are solid, and by using them I avoid the headaches I might incure by choosing the cheapest AMD reccomended supply I can find that week.

[Kaipora]

i like Enermax too, but people have been talking about Sparkle recently. anyone work with the PSU's. how about some opinions?