Archived from groups: alt.comp.periphs.mainboard.asus (
More info?)
Geez -
I'm going to have to go to night school!
But I'll try to understand your reply and see if I can figure it all out.
Thanks for the thorough reply
Richard
"Paul" <nospam@needed.com> wrote in message
news:nospam-0406050744410001@192.168.1.178...
> In article <ON7oe.41071$_r1.1290860@news20.bellglobal.com>, "Richard Lees"
> <r_lees001@hotmail.com> wrote:
>
>> Slightly off-topic, but relevant to many - I hope.
>>
>> I have a power supply that was given to me. The previous owner is
>> suspicious that it may be the cause of all his PC woes (hence the free
>> gift)
>> How do I go about testing it to see if it is OK in regards to correct
>> voltages.
>>
>> It's laying on my desk at the moment. Do I have to install it in a case
>> to
>> test it, or can I test it 'on the bench'?
>> What exactly am I looking for anyway?
>> The 20 pin connector has many colored wires, Are the colours
>> significant?
>> How do I test for 12, 5 and 3 volts??
>>
>> Sorry for the newbie-like question, but It would be a shame to throw it
>> in
>> the garbage without checking it out first.
>>
>> Many thanks
>> Richard
>
> Pinout is on page 19:
>
http://www.formfactors.org/developer/specs/atx/atx2_1.pdf
>
> (pin 1) (pin 11)
> +3.3VDC +3.3VDC
> +3.3VDC -12VDC
> COM COM
> +5VDC PS_ON# <--- connect to COM to start PSU.
> COM COM <--- Plastic lock latch is
> +5VDC COM <--- next to these pins.
> COM COM
> PWR_OK -5VDC
> +5VSB +5VDC
> +12VDC +5VDC
>
> You have six voltages to test:
>
> +5VSB - standby supply for sleeping computer, also powers start up
> circuit on PSU. If not at full 5 volts, PSU may not work
> properly, as supervisor cct in PSU will not be properly powered.
> For the PSU to be completely turned off, PS_ON# should float
> near the same +5VSB voltage. When PS_ON# is grounded (to COM),
> the supply runs.
> +3.3VDC - Used by PCI/AGP cards for chip power. May be used for
> memory power, via linear regulation.
> +5VDC - Used to power Vcore switching regulator on Asus AthlonXP boards.
> Video card power, disk drive power.
> +12VDC - Used to power Vcore switching regulator on P4/Athlon64 boards.
> Video card power, disk drive power.
> -5V - Historically, used for ECL or really old tech, three rail
> DRAM memories. Maybe some kind of video card RAMDAC.
> Typically not used today. Possibly used in linear (op amp)
> circuits.
> -12V - On Asus boards, can be used for RS-232 converter chip. Also
> potentially used for op amps in linear regulators. It is hard
> to say which negative rail Asus would use on their op-amp
> circuits, as negative swings are not really required. In any
> case 0.1 amps of consumption on a motherboard is probably
> a reasonable estimate.
>
> A quick test, is to connect PS_ON# to a COM pin. The plastic lock
> latch will help guide you to the right cluster of pins. The purpose
> of a quick test, is just to check that the PSU fan starts to spin.
> That would only prove that the supervisory circuit is capable of
> turning on, in a situation where, say, a motherboard refuses to start.
>
> To quantify operation, you need a load on the PSU. One choice
> is to apply the minimum load necessary for proper regulation.
> Some supplies have minimum current loads specified on the label
> on the side of the supply. If you draw that minimum current, then
> the output is guaranteed to be within 5% of the proper voltage.
> One would hope, under those conditions, it is a lot closer than
> that.
>
> To measure the output, you will need a voltmeter. Home units are
> typically not that good, and my $100 CDN meter is good to about
> 1.5% to 2% accuracy, depending on range used. That means there is
> room for doubt in the readings, to those precentages.
>
> Drawing the minimum supply current ensures the outputs will be in
> spec. A second test would be a load test, using a representative
> load. Using a load like this, proves the power supply will be
> able to run a real motherboard - the load circuit takes the risk
> out of having to connect a real motherboard, to prove the power
> supply works.
>
> Here are some representative loads measured on systems here:
>
> A7N8X (3200+) P4C800-E (2.8GHz)
> 3 DIMMs 4 DIMMs
> +3.3V 5.5A 13.75A
> +5.0V 16 + 5.5A 0.6 + 5.5A
> +12.0V 0.5 + 0.9A 6.4 + 0.9A
>
> The added currents shown above (5.5A and 0.9A) are for a 9800pro
> AGP video card while gaming. The 6.4A for the P4, is 6 amps for the
> processor and 0.4A for the processor fan.
>
> To build a load tester, you will need a cable harness (snip up
> a 20 to 24 pin adapter cable - even a 24 pin connector can be
> used for the project, as there is only one way to plug a 20 pin
> power supply into such a connector, and have all the pins
> connected). You will also need resistors.
>
> To work out a load resistance:
>
> V/I = R_load = 3.3V/5.5A = 0.6 ohms
>
> V*I = power_dissipation = 3.3V*5.5A = 18.15 watts
> Can also be calculated as V*V/R, if only V and R are known.
>
> More than one resistor can be used to build a load. Two 0.3 ohm
> resistors put in series, would give a 0.6 ohm load. Two 1.2 ohm
> resistors put in parallel, would give a 0.6 ohm load. The
> power dissipated in each case, is now split between the two
> resistors, so two smaller resistors can be used to make a larger
> resistor. In the third example below, a square matrix of resistors
> of equal value, can be used. In that case, each resistor only
> needs to handle 1/9th of the total power to be dissipated.
>
> ----- 0.3 ------ 0.3 ------ = 0.6 ohms
>
> ---+--- 1.2 ---+--- = 0.6 ohms = R1*R2/(R1+R2)
> | |
> +--- 1.2 ---+
>
> ----+--- 0.6 ---+--- 0.6 ---+--- 0.6 ---+----- = 0.6 ohms
> | |
> +--- 0.6 ---+--- 0.6 ---+--- 0.6 ---+
> | |
> +--- 0.6 ---+--- 0.6 ---+--- 0.6 ---+
>
> (Hint - the parallel configuration may be easier to construct
> - a ladder constructed of stiff copper house wiring
> could be used to mount resistors in parallel.)
>
> There are many styles of power resistors. In the two examples
> below, one is designed for free-standing operation. The other
> one is intended for use with a heat sink (but no thermal data
> is given?). In the load examples in the table above, the 5V
> at 21.5 amp load would be the hardest one to cool, at 108 watts.
> For some resistors I've been looking at, they appear to be
> intended to dissipate the rated power without forced air, but
> if you run a fan over them, you might not burn yourself on
> them.
>
> There are some candidate resistors here. To reach our target
> resistances using these products, in some cases, multiple
> resistors are needed (in parallel) to get the resistance low
> enough. In other cases, multiple resistors are needed to get
> enough power handling capability. As the Digikey catalog
> doesn't have all possible resistor values, sometimes a higher
> power resistor must be substituted to get a necessary resistor
> value. (I.e. The selection process is a mess. I did all the
> math necessary, to build my load box, while standing in front
> of the power resistor display rack at my local electronics
> store. That is because you never know what resistors will be
> in stock...)
>
> FVT series: The FVT are fixed value resistors. Vitreous enamel
> looks to be a high temperature material, so you can burn the
> hell out of these.
>
>
http://dkc3.digikey.com/PDF/T052/1075.pdf
>
> The TMC ones (second item from top of page) have a casing suitable
> for use with a heatsink. Now, there simply isn't enough data
> here, to design with these and understand what you are doing.
> (No thermal resistance data, for example.) How many of these
> could you bolt to one heatsink ?
>
>
http://dkc3.digikey.com/PDF/T052/1076.pdf
> ==>
http://www.heiresistors.com/aluminum.htm
>
> A7N8X (3200+) P4C800-E (2.8GHz)
> 3 DIMMs 4 DIMMs
> +3.3V 5.5A => 0.6ohm 18W 13.75A => 0.24ohm 45W
> +5.0V 21.5A => 0.23ohm 108W 6.1A => 0.82ohm 31W
> +12.0V 1.4A => 8.6ohm 17W 7.3A => 1.64ohm 88W
> totals 143W 164W
>
> now select some resistor combinations...
>
> A7N8X (3200+) P4C800-E (2.8GHz)
> 3 DIMMs 4 DIMMs
> +3.3V 5.5A => 0.6ohm 18W 13.75A => 0.24ohm 45W
> (3) FVT25-2.0-ND in (4) FVT50-1.0-ND in
> parallel $9.93 parallel $19.16
>
> +5.0V 21.5A => 0.23ohm 108W 6.1A => 0.82ohm 31W
> (4) FVT50-1.0-ND in (1) FVT50-1.0-ND parallel with
> parallel $19.16 (1) FVT50-5.0-ND $9.58
>
> +12.0V 1.4A => 8.6ohm 17W 7.3A => 1.64ohm 88W
> (1) FVT25-10-ND $3.28 (1) FVT100-2.0-ND parallel with
> (1) FVT25-10-ND $11.49
>
> -5V (1) FVT25-25-ND $3.28 (1) FVT25-25-ND $3.28
> will draw 0.2 amps will draw 0.2 amps
>
> -12V (1) FVT50-50-ND $4.50 (1) FVT50-50-ND $4.50
> will draw 0.24 amps will draw 0.24 amps
>
> +5VSB (1) FVT25-10-ND $3.28 (1) FVT25-10-ND $3.28
> will draw 0.5 amps will draw 0.5 amps
>
> Total $43 for resistors $51 for resistors
> + 80mm fan for cooling 80mm fan for cooling
>
> Wiring the A7N8X example:
>
> +3.3 ----+----+----+
> | | |
> 2ohm 2ohm 2ohm
> | | |
> COM ----+----+----+
>
> +5.0 ----+----+----+----+
> | | | |
> 1ohm 1ohm 1ohm 1ohm
> | | | |
> COM ----+----+----+----+
>
> +12.0 ----+-----------+
> | | (red)
> 10ohm 80mm fan
> | | (black)
> COM ----+-----------+
>
> -5V ----+
> |
> 25ohm
> |
> COM ----+
>
> -12V ----+
> |
> 50ohm
> |
> COM ----+
>
> +5VSB ----+ PS_ON+ ----+
> | |
> 10ohm (toggle switch)
> | |
> COM ----+ COM ----+
>
> Note: This is just to give you some ideas for how to construct
> your own PSU load box. If you can find cheaper resistors, you
> will be able to use more of them, and perhaps have them run a
> bit cooler. The FVT100-2.0-ND resistor on the right hand example
> is going to get pretty hot. When using the 80mm fan, it might
> be a good idea to build a "wind tunnel" with sheet metal, to
> shape the airflow around the resistors.
>
> You will also want some place to probe with your volt meter.
> So, if building vertical ladders with copper wire, screwed down
> to a wooden base, leave enough excess wire on the ends of the
> ladder, so you can probe with the voltmeter.
>
> When testing the PSU, run it with the representative load for
> a couple of hours, and see if all voltages are still within
> 5% of the stated values.
>
> There is no point testing the "full power" rating of the
> supply, because many commonly available power supplies will
> disappear in a cloud of smoke if you do that. The idea of a
> load test, is to present a representative load, similar to
> the motherboard you will be using.
>
> The power supply test products that have LED indicators on
> them, could be using a window comparitor circuit. For example,
> if one analog comparator checks for 11.4V, and another one checks
> for 12.6V, using some logic gates, those comparators can be
> used to check that the voltage is within the "window" of
> 11.4V <= V_out <= 12.6V. Under those conditions, the LED comes
> on. If the voltage is outside the window, the LED goes off.
> You can get the same information by simply measuring the output
> with a voltmeter.
>
> P.S. I'm not responsible if you burn yourself on the resistors!
> They can get really hot (resistors rated to 350C degrees), so
> don't be poking them with your fingers. As long as there is a
> decent airflow with the cooling fan, that should prevent them
> from getting all the way to 350C. Make sure there is some
> separation between the resistor and any combustable material.
> Using bare copper wire to hook up the resistors will avoid
> the embarrassment of having the wire insulation start to burn.
> And, above all, don't run this gadget unattended - turn it off
> and unplug it, if you leave the room. Think of having to explain
> to the insurance agent about power supply testers
>
> Is it worth $100 for test gear (tester+voltmeter), to test a
> $30 power supply ? Only you can answer that. I built my tester,
> just to make sure I don't kill any expensive motherboards. My
> tester draws less current than the examples above.
>
> Have fun,
> Paul
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