Is my power supply enough?

[Skuzzy]

A lot of talk about how much power your computer needs has been going on lately.  With all the talks about lock-ups and so on, so I thought I would lend a bit of information that might help.

Most modern day BIOS roms can show you the voltage levels of the various voltages required in your computer system.
This is usually listed in the same place as the temperature for the CPU is.

If you are concerned that you are pushing your power supply, or just need to know you are ok, you can look at these line levels which will show if you need a bigger supply or not.

The primary line levels you should look at, are the +5 and +12 volt lines.  The +5 vlot line is used to drive just about every logic component in your computer, except for the CPU.
The +12 volt line is used for serial communication devices (ethernet, modem...) and the various electro-mechanical devices (mostly the hard drive).

After booting into your BIOS rom and navigating to this display, you should watch it for a minute or so.  the +5 volt line level should be a little more than 5V and the +12 volt line should be a little more than 12V.
If your +5 volt line level is lower than 4.9V and consistently stays there, you should consider a new power supply.
If your +12 volt line drops below 11.5V and stays there consistently, you may want to move your hard drive to an external case, or get a bigger power supply.  Some CD drives use the 12V line for the motor in the drive.  While monitoring the line levels, put in a CD, as it will start the motor and watch the +12 line level.  It should drop to about 11.2V and quickly recover back to 12V.  If it takes a few seconds to get back to 12V, then you are on the hairy edge of needing a new supply.

Hope that helps.

------------------
Roy "Skuzzy" Neese
President, AppLink Corp.
http://www.applink.net
skuzzy@applink.net

[Lephturn]

You can also use a program like Motherboard Monitor to monitor your voltages while you play AH.  You can set alarms to activate if the voltages get too far out of spec.  This is a good test, since you will be able to have the monitor running while actually using the computer.

You can get it here:  http://mbm.livewiredev.com/

Set your alarm thresholds as Skuzzy suggests and fire up AH for an hour or so.  

------------------
Sean "Lephturn" Conrad - Aces High Chief Trainer

A proud member of the mighty Flying Pigs
http://www.flyingpigs.com

Check out Lephturn's Aerodrome for AH articles and training info!

[-lynx-]

...Alternatively you can use the sound of you fan - if it's changing frequencies under load - good indications that this is not 300W PSU as it says on the box...  

[Skuzzy]

Can't really go by that lynx.  Most power supplies have variable speed fans these days that are driven by the temperature of the supply.

------------------
Roy "Skuzzy" Neese
President, AppLink Corp.
http://www.applink.net
skuzzy@applink.net

[bloom25]

Skuzzy, I thought I might add to your post here if I might.  

There are 2 more things that should be considered here:

1.  The 3.3V level is VERY important for the PCI and AGP cards in your system, as well as the system RAM.  If this is spiking you can bet that lockups will result.

2.  Another important, but little known issue, with power supplies is the 5V+ VSB or 5V standby power.  Many newer systems have the ability to put themselves to sleep.  Unfortuately waking from this "sleep" mode often is troublesome.  (Kind of like me in the morning.   )  The problem is usually due to the fact that the 5v VSB is only rated at .5A.  This should be a minimum of 1A, and 1.5A is even better.

3.  AMD Athlon/Duron users should check the recommended power supply list on AMD's website.  My experences are that Antec and Sparkle Power supplies have been the best.  You can also look at the sticker on the power supply, specifically look for a statement like: "The combined power of the 3.3 and 5V leads is 125W."  AMD users will want this to be a minimum of 125W, and 150W is preferred.  Basically what this is is the power that can be provided to the MB itself (and thus video card etc) via the ATX power connector.  The importance of this becomes evident when considering that a 1200 Mhz Tbird dissipates over 50W of HEAT alone!  If you add in a GF2 Ultra card dissipating 40W by itself, well, you get the picture!  

Look here guys, these are good powersupplies:
 http://www1.amd.com/athlon/npower/index/1,1712,,00.html



------------------
bloom25
-MAW-
(Formerly of the)
THUNDERBIRDS

[qts]

I think he's referring to the CPU fan there.

However, I'm a firm believer in excess, especially when you have a heavily stuffed box. If MS say 64 MB, go for 256 MB; if AMD say go for a 300W PSU, go for a 400W one. You won't regret it.

------------------
qts

[TheWobble]

Well if your a stingy turdball like me but still have very power demanding components like a V5 and a Athlon processor you only have a 250w PS ya can always go the cheap route and slap another 250w form yer old case in and use it to run your hard disks, CD-Roms, floppy, and fans..freeing up enough for the other 250 to not be burdemed...sounds odd but works very well.

[-lynx-]

I take it wobble is not drunk cuz he might be onto something - thanks, I'll try that (have a brand new AT PSU lurking about somewhere and a great AOpen case with shedload of space inside)

And yes, I was talking about the CPU fan, I can hear the change in it's whine frequency quite clearly when the machine goes "under stress"

[Skuzzy]

Not at all bloom.  The only reason I did not mention the 3.3V line, was due to the low loading of the line.  If the power supply is hitting the numbers on the +5V line, it would be difficult for it not to make the 3.3V numbers as the +5V line is the highest loaded line, after the system is up and running.  During power up, the +12V line is usually higher due to the startup requirements of the hard drive.

I can further augment as I just saw a post that I find a bit troublesome.

Folks, there are many ways to rate power supplies.  First, the rated power of the supply is only a small portion of the performance the supply can achieve.
Switching power supplies can be fast or slow.  In other words, the time they take to discharge and recharge the capacitors in the supply can vary.  High quality power supplies are usually very fast.  Low cost, budget power supplies use slower capacitors and regulators.
Also, the total rated power has nothing to do with how the power is apportioned to the various voltage levels the power supply has to deal with.
This is why you must check the voltage line levels in your system from time to time.  Why?  Over time the capacitors in the power supply will lose thier ability to store/discharge power at the required rate of your system.  This will have a huge impact on really fast systems that can dissipate power very quickly.

Dispelling another myth,....."bigger is always better".  NOT true for power supplies.  If you are using a linear power supply, then yes, this would be true.  BUT switching power supplies deliver the best power (i.e. cleanest) when they run between 90 and 95 pecent of thier rated capacity.
If you have a power supply that is running at 50% or less capacity, then you end up with dirty power delivery, as the capacitors in the power supply are constantly full and must use other paths to discharge the power  (usually ground).  This switching of the path causes spikes on the power being delivered to your system.  Small surges to your components, which over time, will cause premature failure to occur.  These small surges can also cause other anomalies, if they propogate through the system.

I could go on about the capacitance of the transistors and how they transfer that power, which leads to the propogation, but I hope this is enough.


------------------
Roy "Skuzzy" Neese
President, AppLink Corp.
http://www.applink.net
skuzzy@applink.net

[whels1]

Hi skuzzy,

i checked the 2 voltages, the +5 is at
4.91 and stays there solid, no up or down.
the +12 is 12.10 to 12.16 steady even
doing the cd thing. its a 250w PS, what would u suggestion be? i dont have any locks but do get stutters sometimes.

whels

 

Originally posted by Skuzzy:
A lot of talk about how much power your computer needs has been going on lately.  With all the talks about lock-ups and so on, so I thought I would lend a bit of information that might help.

Most modern day BIOS roms can show you the voltage levels of the various voltages required in your computer system.
This is usually listed in the same place as the temperature for the CPU is.

If you are concerned that you are pushing your power supply, or just need to know you are ok, you can look at these line levels which will show if you need a bigger supply or not.

The primary line levels you should look at, are the +5 and +12 volt lines.  The +5 vlot line is used to drive just about every logic component in your computer, except for the CPU.
The +12 volt line is used for serial communication devices (ethernet, modem...) and the various electro-mechanical devices (mostly the hard drive).

After booting into your BIOS rom and navigating to this display, you should watch it for a minute or so.  the +5 volt line level should be a little more than 5V and the +12 volt line should be a little more than 12V.
If your +5 volt line level is lower than 4.9V and consistently stays there, you should consider a new power supply.
If your +12 volt line drops below 11.5V and stays there consistently, you may want to move your hard drive to an external case, or get a bigger power supply.  Some CD drives use the 12V line for the motor in the drive.  While monitoring the line levels, put in a CD, as it will start the motor and watch the +12 line level.  It should drop to about 11.2V and quickly recover back to 12V.  If it takes a few seconds to get back to 12V, then you are on the hairy edge of needing a new supply.

Hope that helps.

[PJ]

I recently upgraded my old P3 600/BX440 to a P3 1ghz and a D815EPEA mobo and was having all sorts of instability so I dumped the 235watt PSU and bought myself an Enermax 330watt; result,complete stability at last. Just my 2pence worth.

[Sky Viper]

 

Originally posted by whels1:
Hi skuzzy,

i checked the 2 voltages, the +5 is at
4.91 and stays there solid, no up or down.
the +12 is 12.10 to 12.16 steady even
doing the cd thing. its a 250w PS, what would u suggestion be? i dont have any locks but do get stutters sometimes.

whels

 

<Dusts off the old USN Avionics Braincells>

The problem with what Skuzzy is indicating is that he is strictly considering Voltage and not current.
Some power supplies maintain steady voltage by design. So, even when the current drops, the Voltage reading will remain steady on the Bios or Software monitor. These PS are so designed to help prevent lockups due to digital components having a low voltage supply.  Digital components are generaly less current dependant.

The problem with these types is that they don't necessarily supply enough current to maintain stability while running several high current devices.

Basic Electronics:
P=I*E or Power= Current * Voltage.
E=I*R or Voltage= Current * Resistance.
By maintaing Constant E (Volts) and increasing R (HDD access, Joystick inputs, sounds played etc...) you are forcing "I" (Current) to decrease.
Example:
12V  2ohms(R) = 6 AMPs(I)
Move a joystick and 2ohms becomes 3, 12V stays, and 6A becomes 4. Now the PS has to make up for that 2A draw.  You won't see this on most BIOS Voltage monitors.

If the PS is large enough, then the power is in reserve so to speak.

If you have problems such as lockups or stutters at 250W, it may be worth it try a 300W supply.

Bottom line:
Nothing is a better measure than a stable system.

------
Whels, your stutters may also have other causes.  It helps to know what kind of stutters you mean.

Ex. I use your sounds, and when I put the gear up in my Hawgs, I get a split second stutter while the sound file loads. Slow HDD access, large file not yet in memory etc.

Viper

[-lynx-]

 

Basic Electronics:
P=I*E or Power= Current * Voltage.
E=I*R or Voltage= Current * Resistance.
By maintaing Constant E (Volts) and increasing R (HDD access, Joystick inputs, sounds played etc...) you are forcing "I" (Current) to decrease.
Example:
12V 2ohms(R) = 6 AMPs(I)
Move a joystick and 2ohms becomes 3, 12V stays, and 6A becomes 4. Now the PS has to make up for that 2A draw. You won't see this on most BIOS Voltage monitors.

If the PS is large enough, then the power is in reserve so to speak.

Uh-oh - that's wrong I'm afraid. The formulas are correct it's their application that is somewhat flawed: additional devices draw more power, not add resistance. That is, they sit on a power bus in parallel, not as a chain - I wish I knew proper English terms for it but I hope you get my drift  

Each device has internal power consumption based on it's power output. If a PSU is able to supply enough power for all devices - the voltage is maintained. If you "ask" for more power than it can provide - the voltage drops and all bad things happen.

Eg: your puter draws 200 watts of power in a 5V line (all you devices "eat" 40A of current at 5V - Power=Voltage*Current). If your PSU is rated to supply at least 40A at 5V - everything is fine. Then you add a V5 5500 and the PSU is no longer able to provide enough power to drive the beastie - the voltage drops. It's that simple.

To say that you have "a 300W PSU" means not a lot either - everything depends on what the PSU is able to supply (powerwise) at each voltage and how much your system is drawing at those voltages. For example, you may have plenty of powew left to run few more 5V things but all those extra fans spread inside you case like cancer   draw all awailable 12V power - you plug another HD in and the whole system starts hic-cupping...

[This message has been edited by -lynx- (edited 04-18-2001).]

[Sky Viper]

 

Originally posted by -lynx-:
 

Basic Electronics:
P=I*E or Power= Current * Voltage.
E=I*R or Voltage= Current * Resistance.
By maintaing Constant E (Volts) and increasing R (HDD access, Joystick inputs, sounds played etc...) you are forcing "I" (Current) to decrease.
Example:
12V 2ohms(R) = 6 AMPs(I)
Move a joystick and 2ohms becomes 3, 12V stays, and 6A becomes 4. Now the PS has to make up for that 2A draw. You won't see this on most BIOS Voltage monitors.

If the PS is large enough, then the power is in reserve so to speak.

Uh-oh - that's wrong I'm afraid. The formulas are correct it's their application that is somewhat flawed: additional devices draw more power, not add resistance. That is, they sit on a power bus in parallel, not as a chain - I wish I knew proper English terms for it but I hope you get my drift   (Image removed from quote.)

Each device has internal power consumption based on it's power output. If a PSU is able to supply enough power for all devices - the voltage is maintained. If you "ask" for more power than it can provide - the voltage drops and all bad things happen.

Eg: your puter draws 200 watts of power in a 5V line (all you devices "eat" 40A of current at 5V - Power=Voltage*Current). If your PSU is rated to supply at least 40A at 5V - everything is fine. Then you add a V5 5500 and the PSU is no longer able to provide enough power to drive the beastie - the voltage drops. It's that simple.

To say that you have "a 300W PSU" means not a lot either - everything depends on what the PSU is able to supply (powerwise) at each voltage and how much your system is drawing at those voltages. For example, you may have plenty of powew left to run few more 5V things but all those extra fans spread inside you case like cancer    (Image removed from quote.) draw all awailable 12V power - you plug another HD in and the whole system starts hic-cupping...

[This message has been edited by -lynx- (edited 04-18-2001).][/b]

HEHE...yeah..."Chain" = "Series".

And, it's not flawed.  

Viper

[Skuzzy]

Viper, the current draw is the most critical compnonet of power delivery, never saud it was not, but the BIOS does not show the power being delivered, only the voltage levels.
Now, understand the components that display this level in the BIOS are leading edge triggered devices.  That is, they only show the voltage level of the leading edge of the signal.
This edge will always be higher than the trailing edge of the signal, unless the power supply is reaching its capacity or over its capacity to deliver the current needed. At the point of saturation, the leading edge of the signal will not surge, but will in fact start to slope up slower.
This will be shown as a lower voltage level by the BIOS utility.
That is why you can use the BIOS voltage levels as a good guide to know when you are close to saturating the power supply.

------------------
Roy "Skuzzy" Neese
President, AppLink Corp.
http://www.applink.net
skuzzy@applink.net