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How much power surge is there at startup? + other questions

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Anonymous
a b B Homebuilt system
February 11, 2005 11:01:35 AM

Archived from groups: alt.comp.hardware.pc-homebuilt;,alt.comp.hardware.homebuilt (More info?)

Several power-related questions:

Do ball-bearing fans and disk drives draw a lot of extra power when they
start up after the system is turned on? If so, how much, and what
effect does this have on proper sizing of the power supply? How long
does the extra power requirement last?

I recall that some disk drives that I've used in the past have some sort
of deferred startup: they wouldn't start until the first command
arrived, or something like that. The idea was to draw less power at the
instant the machine is turned on. Is this still done? The drives I
bought came without instructions, just in an anti-static pack.

And another related question: does putting a fan under load (by having
a filter in front of it, for example) increase power consumption as well
as slowing the fan down?

Finally, how does the power requirement of a PC interrelate with the
voltages provided by the PSU? Do these voltages decline even when load
is well below the nameplate capacity of the PSU, or do they drop only
when the load approaches the limit, or what? According to my
calculations, my power supply is loaded at barely a third of its
nameplate capacity, but the 12V supply is still just a tad below 12V
most of the time.

--
Transpose hotmail and mxsmanic in my e-mail address to reach me directly.

More about : power surge startup questions

Anonymous
a b B Homebuilt system
February 11, 2005 11:01:36 AM

Archived from groups: alt.comp.hardware.pc-homebuilt,alt.comp.hardware.homebuilt (More info?)

Mxsmanic wrote:
> Several power-related questions:
>
> Do ball-bearing fans and disk drives draw a lot of extra power when they
> start up after the system is turned on?

Yes

> If so, how much, and what
> effect does this have on proper sizing of the power supply? How long
> does the extra power requirement last?

It's of relatively short duration and the surge capacity of the PSU is
usually sufficient.


> I recall that some disk drives that I've used in the past have some sort
> of deferred startup: they wouldn't start until the first command
> arrived, or something like that. The idea was to draw less power at the
> instant the machine is turned on. Is this still done? The drives I
> bought came without instructions, just in an anti-static pack.
>
> And another related question: does putting a fan under load (by having
> a filter in front of it, for example) increase power consumption as well
> as slowing the fan down?

It depends on the fan's efficiency vs static pressure curve and how much
static pressure is introduced by the filter. But unless you're installing a
building air conditioning system, don't worry about it. Airflow is a
bigger issue.


> Finally, how does the power requirement of a PC interrelate with the
> voltages provided by the PSU? Do these voltages decline even when load
> is well below the nameplate capacity of the PSU,

Not if it's working properly.

> or do they drop only
> when the load approaches the limit, or what?

Might drop on overload, just before overload protection kicks in and turns
it off.

> According to my
> calculations, my power supply is loaded at barely a third of its
> nameplate capacity, but the 12V supply is still just a tad below 12V
> most of the time.

Everything has tolerances (there's no such thing as a "1 inch hole." [and
even if there was you couldn't know because your measuring device has
tolerances] It's 1 inch, plus or minus some tolerance, hole) and a 'tad',
whatever that is, is fine as long as it's within the specified tolerances.
Anonymous
a b B Homebuilt system
February 12, 2005 2:09:35 AM

Archived from groups: alt.comp.hardware.pc-homebuilt;,alt.comp.hardware.homebuilt (More info?)

On Fri, 11 Feb 2005 08:01:35 +0100, Mxsmanic
<mxsmanic@hotmail.com> wrote:

>Several power-related questions:
>
>Do ball-bearing fans and disk drives draw a lot of extra power when they
>start up after the system is turned on?

Fans don't usually make enough of a difference, relatively
speaking it would take very many to matter. HDDs though do
generally consume 2-3X as much 12V power.

> If so, how much, and what
>effect does this have on proper sizing of the power supply?

Mostly it can take the drives longer to spin up, and with a
modern system that could mean some aren't properly detected
because everyone seems in a hurry to get past the POST
enumeration and onto windows. If your PSU is sufficient
for the everyday running of the system it should have enough
reserve to spin up the drives too... though it's never a
good idea to rapidly power-cycle a power supply on and off
over and over and over.

> How long
>does the extra power requirement last?

A few seconds, maybe 2, 3, 4...



>
>I recall that some disk drives that I've used in the past have some sort
>of deferred startup: they wouldn't start until the first command
>arrived, or something like that. The idea was to draw less power at the
>instant the machine is turned on. Is this still done? The drives I
>bought came without instructions, just in an anti-static pack.

Tpical PC drives don't wait. Some SCSI can. It's not much
of an issue unless you were trying to power too many drives
from too small a PSU. ALways use a quality PSU befitting
the parts it's powering, it is not the place to try to save
an extra $20 (over cost of a lesser PSU).


>
>And another related question: does putting a fan under load (by having
>a filter in front of it, for example) increase power consumption as well
>as slowing the fan down?

Not significantly relative to the load on that power rail.
Fans really don't use much power at all, a dozen of (typical
size & speed fans) is less load than a single HDD spinning
up. Percentagewise it might be possible the fan uses a tiny
bit more power, honestly I don't know and don't think it
matters enough to find out. Fans don't actually draw the
entire amperage stamped on their label more often than not.

>
>Finally, how does the power requirement of a PC interrelate with the
>voltages provided by the PSU? Do these voltages decline even when load
>is well below the nameplate capacity of the PSU, or do they drop only
>when the load approaches the limit, or what?

They drop the voltage relative to the capacity of that power
rail which is determined by a voltage monitored by the PSU.
Typically that is at least the 5V rail and often a weighted
measurement of the 12V rail too. In other words, you should
be able to add parts and expect the voltage to remain within
an acceptable range until the unit is overloaded OR until
there is a drastic imbalance of power draw. For example if
you had a high-end workstation power supply that has 25A of
12V capacity but only 35A of 5V, and you use a motherboard
that draws a lot of 5V power but had no HDDs connected, you
might find the power supply shuts off due to sensing a 12V
rail that's drifted too high. The rail might not be over
the 10% official spec per 12V rail but some PSU are even
tighter than 10%.


>According to my
>calculations, my power supply is loaded at barely a third of its
>nameplate capacity, but the 12V supply is still just a tad below 12V
>most of the time.

Did you measure this with a multimeter or by the
motherboard sensors? MOtherboard sensors are notoriously
inaccurate, if the PSU is outputting 12.0V (exactly) the
sensors will typically register lower due to trace
resistance. Sometimes a lot lower, maybe even 11.6V if
overclocking. You really need to use a multimeter at the
connector attached to the load (which in this case is the
motherboard ATX or 4-pin connectors for 12V).
Related resources
Anonymous
a b B Homebuilt system
February 12, 2005 2:09:36 AM

Archived from groups: alt.comp.hardware.pc-homebuilt;,alt.comp.hardware.homebuilt (More info?)

In article <ppeq0118g6khlgnsh8gnoiluf6dl1brj24@4ax.com>,
kony <spam@spam.com> wrote:
>On Fri, 11 Feb 2005 08:01:35 +0100, Mxsmanic
><mxsmanic@hotmail.com> wrote:
>
>>Several power-related questions:
>>
>>Do ball-bearing fans and disk drives draw a lot of extra power when they
>>start up after the system is turned on?
>
>Fans don't usually make enough of a difference, relatively
>speaking it would take very many to matter. HDDs though do
>generally consume 2-3X as much 12V power.
>
>> If so, how much, and what
>>effect does this have on proper sizing of the power supply?
>
>Mostly it can take the drives longer to spin up, and with a
>modern system that could mean some aren't properly detected
>because everyone seems in a hurry to get past the POST
>enumeration and onto windows. If your PSU is sufficient
>for the everyday running of the system it should have enough
>reserve to spin up the drives too... though it's never a
>good idea to rapidly power-cycle a power supply on and off
>over and over and over.
>
>> How long
>>does the extra power requirement last?
>
>A few seconds, maybe 2, 3, 4...
>

I'd guess that charging all the capacitors on the mobo is
a big part of the power-on surge.


>
>
>>
>>I recall that some disk drives that I've used in the past have some sort
>>of deferred startup: they wouldn't start until the first command
>>arrived, or something like that. The idea was to draw less power at the
>>instant the machine is turned on. Is this still done? The drives I
>>bought came without instructions, just in an anti-static pack.
>
>Tpical PC drives don't wait. Some SCSI can. It's not much
>of an issue unless you were trying to power too many drives
>from too small a PSU. ALways use a quality PSU befitting
>the parts it's powering, it is not the place to try to save
>an extra $20 (over cost of a lesser PSU).
>
>
>>
>>And another related question: does putting a fan under load (by having
>>a filter in front of it, for example) increase power consumption as well
>>as slowing the fan down?
>
>Not significantly relative to the load on that power rail.
>Fans really don't use much power at all, a dozen of (typical
>size & speed fans) is less load than a single HDD spinning
>up. Percentagewise it might be possible the fan uses a tiny
>bit more power, honestly I don't know and don't think it
>matters enough to find out. Fans don't actually draw the
>entire amperage stamped on their label more often than not.
>
>>
>>Finally, how does the power requirement of a PC interrelate with the
>>voltages provided by the PSU? Do these voltages decline even when load
>>is well below the nameplate capacity of the PSU, or do they drop only
>>when the load approaches the limit, or what?
>
>They drop the voltage relative to the capacity of that power
>rail which is determined by a voltage monitored by the PSU.
>Typically that is at least the 5V rail and often a weighted
>measurement of the 12V rail too. In other words, you should
>be able to add parts and expect the voltage to remain within
>an acceptable range until the unit is overloaded OR until
>there is a drastic imbalance of power draw. For example if
>you had a high-end workstation power supply that has 25A of
>12V capacity but only 35A of 5V, and you use a motherboard
>that draws a lot of 5V power but had no HDDs connected, you
>might find the power supply shuts off due to sensing a 12V
>rail that's drifted too high. The rail might not be over
>the 10% official spec per 12V rail but some PSU are even
>tighter than 10%.
>
>
>>According to my
>>calculations, my power supply is loaded at barely a third of its
>>nameplate capacity, but the 12V supply is still just a tad below 12V
>>most of the time.
>
>Did you measure this with a multimeter or by the
>motherboard sensors? MOtherboard sensors are notoriously
>inaccurate, if the PSU is outputting 12.0V (exactly) the
>sensors will typically register lower due to trace
>resistance. Sometimes a lot lower, maybe even 11.6V if
>overclocking. You really need to use a multimeter at the
>connector attached to the load (which in this case is the
>motherboard ATX or 4-pin connectors for 12V).
>


--

a d y k e s @ p a n i x . c o m

Don't blame me. I voted for Gore.
Anonymous
a b B Homebuilt system
February 12, 2005 5:37:56 AM

Archived from groups: alt.comp.hardware.pc-homebuilt;,alt.comp.hardware.homebuilt (More info?)

kony writes:

> Did you measure this with a multimeter or by the
> motherboard sensors?

All I have is the motherboard sensors, unfortunately.

> MOtherboard sensors are notoriously
> inaccurate, if the PSU is outputting 12.0V (exactly) the
> sensors will typically register lower due to trace
> resistance. Sometimes a lot lower, maybe even 11.6V if
> overclocking.

Well, that's reassuring, in a way, since it means that the PSU is
probably at 12V even if it doesn't show.

--
Transpose hotmail and mxsmanic in my e-mail address to reach me directly.
Anonymous
a b B Homebuilt system
February 20, 2005 5:46:52 PM

Archived from groups: alt.comp.hardware.pc-homebuilt,alt.comp.hardware.homebuilt (More info?)

As an aside, power surge at startup re draw from the utility-co
is actually quite high for SMPS. An input draw 30A or even 60A
is not uncommon even for very small PSUs (120-150W), and the
really big SMPS can draw over 200A surge at turn on.

One reason why you see the electricity meter kick sharply for a
barely perceptible fraction of a second, then slow down again.
Power devices present a "real load" & "reactive load", if you
are a big company you get billed for both loads.

The only time the input surge at startup matters (mainly from
the big primary side electrolytic capacitors are charging) is if
you are using a battery &/or DC-to-DC convertor (Mini-ITX).

A lot of the Mini-ITX DC-to-DC convertor boards still have a
lot of problems with bigger boards, bigger loads & such like.
Particularly an issue with home/DIY in-car PC solutions.

So if planning a "mini-itx car PC", watch the surge issue, large
devices can cause the DC-to-DC convertor boards to shutdown.
Not fail, simply shutdown & require reset or load lightening. I
also wonder if the capacitors are a bit undersized on some.

For home PCs, it's an issue in choosing UPS - yes you may only
want a few minutes to shutdown, but the UPS must be sized ok.
--
Dorothy Bradbury
www.dorothybradbury.co.uk for quiet Panaflo fans
Anonymous
a b B Homebuilt system
February 20, 2005 6:33:41 PM

Archived from groups: alt.comp.hardware.pc-homebuilt,alt.comp.hardware.homebuilt (More info?)

A power supply that draws that much power on starting has
serious and unacceptable design problems. Even in the 1950s,
TVs had inrush current limiters so that no major current was
present on startup.

Been looking at this question with an oscilloscope scope for
a long time. Have yet to find an electronic appliance that
draws, during powerup, anything much more than steady state
current.

Incandescent bulbs: now there is a device that does have an
inrush current. Typically we design on the assumption that
incandescent bulb will draw as much as 8 times its steady
state current for a very minimal time. But electronics -
properly designed - must have inrush current limiters and not
have a large startup current.

Many who just know without first getting educated will often
assume the inrush current limiter is, instead, an MOV
installed for transient protection. Clearly it could not be.
They don't even know of a device that was standard 50 years
ago. A current limiter example:
http://www.alliedelec.com/catalog/pf.asp?FN=1206.pdf


Dorothy Bradbury wrote:
> As an aside, power surge at startup re draw from the utility-co
> is actually quite high for SMPS. An input draw 30A or even 60A
> is not uncommon even for very small PSUs (120-150W), and the
> really big SMPS can draw over 200A surge at turn on.
>
> One reason why you see the electricity meter kick sharply for a
> barely perceptible fraction of a second, then slow down again.
> Power devices present a "real load" & "reactive load", if you
> are a big company you get billed for both loads.
>
> The only time the input surge at startup matters (mainly from
> the big primary side electrolytic capacitors are charging) is if
> you are using a battery &/or DC-to-DC convertor (Mini-ITX).
>
> A lot of the Mini-ITX DC-to-DC convertor boards still have a
> lot of problems with bigger boards, bigger loads & such like.
> Particularly an issue with home/DIY in-car PC solutions.
>
> So if planning a "mini-itx car PC", watch the surge issue, large
> devices can cause the DC-to-DC convertor boards to shutdown.
> Not fail, simply shutdown & require reset or load lightening. I
> also wonder if the capacitors are a bit undersized on some.
>
> For home PCs, it's an issue in choosing UPS - yes you may only
> want a few minutes to shutdown, but the UPS must be sized ok.
Anonymous
a b B Homebuilt system
February 20, 2005 8:58:53 PM

Archived from groups: alt.comp.hardware.pc-homebuilt,alt.comp.hardware.homebuilt (More info?)

On Sun, 20 Feb 2005 14:46:52 GMT, "Dorothy Bradbury"
<dorothy.bradbury@ntlworld.com> wrote:

>As an aside, power surge at startup re draw from the utility-co
>is actually quite high for SMPS. An input draw 30A or even 60A
>is not uncommon even for very small PSUs (120-150W), and the
>really big SMPS can draw over 200A surge at turn on.

Many use a power resistor and/or thermistor to limit this
somewhat. Similar strategy might be employed where absent
in a DIY supply.
Anonymous
a b B Homebuilt system
February 21, 2005 1:34:32 AM

Archived from groups: alt.comp.hardware.pc-homebuilt,alt.comp.hardware.homebuilt (More info?)

> incandescent bulb will draw as much as 8 times its steady
> state current for a very minimal time. But electronics -

I peak (2 to 4 ms)= 14 times IRMS for a traditional 115 or 230V bulb and 20
times for an Hallogen.
Anonymous
a b B Homebuilt system
February 21, 2005 3:11:13 AM

Archived from groups: alt.comp.hardware.pc-homebuilt,alt.comp.hardware.homebuilt (More info?)

w_tom wrote:
> A power supply that draws that much power on starting has
> serious and unacceptable design problems. Even in the 1950s,
> TVs had inrush current limiters so that no major current was
> present on startup.

1950s TVs weren't using SM power supplies.

>
> Been looking at this question with an oscilloscope scope for
> a long time. Have yet to find an electronic appliance that
> draws, during powerup, anything much more than steady state
> current.

OK, so you're not good at it then.

Just some random examples

http://www.electronicsoutfitter.com/store/ZM300BAPS.htm...

ZALMAN USA ZM300BAPS - 300W Noiseless Power Supply

INRUSH CURRENT LIMIT (@ Cold start at 25 degrees C)- 115 VAC: 60A
230 VAC: 90A

http://www.plasmatvbuyingguide.com/plasmatv/gateway-pla...

Gateway 42" Plasma TV

Input current 3.3. A
Inrush current 60 A p-p/20 ms Max


http://www.necvisualsystems.com/corpus/J/P/xv2930.pdf

NEC XV29

Input current 2 A at 120VAC / 60Hz
Inrush current 50A

http://www.mcmcomputers.co.uk/product_info.php?products...

12V(4A) LCD Monitor Power Adaptor FSP048-10AV

Inrush Current............15A@115VAC or 30A@230VAC cold start at 25°C
Output Voltage............12 VDC
Output Current............0A to 4A
Efficiency................80% min. at full load


> Incandescent bulbs: now there is a device that does have an
> inrush current. Typically we design on the assumption that
> incandescent bulb will draw as much as 8 times its steady
> state current for a very minimal time.


> But electronics -
> properly designed - must have inrush current limiters and not
> have a large startup current.

Define "large."


> Many who just know without first getting educated will often
> assume the inrush current limiter is, instead, an MOV
> installed for transient protection. Clearly it could not be.
> They don't even know of a device that was standard 50 years
> ago. A current limiter example:
> http://www.alliedelec.com/catalog/pf.asp?FN=1206.pdf

And here w_tom goes into his trademark pompous ass routine.


> Dorothy Bradbury wrote:
>
>>As an aside, power surge at startup re draw from the utility-co
>>is actually quite high for SMPS. An input draw 30A or even 60A
>>is not uncommon even for very small PSUs (120-150W), and the
>>really big SMPS can draw over 200A surge at turn on.
>>
>>One reason why you see the electricity meter kick sharply for a
>>barely perceptible fraction of a second, then slow down again.
>>Power devices present a "real load" & "reactive load", if you
>>are a big company you get billed for both loads.
>>
>>The only time the input surge at startup matters (mainly from
>>the big primary side electrolytic capacitors are charging) is if
>>you are using a battery &/or DC-to-DC convertor (Mini-ITX).
>>
>>A lot of the Mini-ITX DC-to-DC convertor boards still have a
>>lot of problems with bigger boards, bigger loads & such like.
>>Particularly an issue with home/DIY in-car PC solutions.
>>
>>So if planning a "mini-itx car PC", watch the surge issue, large
>>devices can cause the DC-to-DC convertor boards to shutdown.
>>Not fail, simply shutdown & require reset or load lightening. I
>>also wonder if the capacitors are a bit undersized on some.
>>
>>For home PCs, it's an issue in choosing UPS - yes you may only
>>want a few minutes to shutdown, but the UPS must be sized ok.
Anonymous
a b B Homebuilt system
February 23, 2005 12:30:12 AM

Archived from groups: alt.comp.hardware.pc-homebuilt;,alt.comp.hardware.homebuilt (More info?)

Mxsmanic wrote:

> Several power-related questions:
>
> Do ball-bearing fans and disk drives draw a lot of extra power when they
> start up after the system is turned on? If so, how much, and what
> effect does this have on proper sizing of the power supply? How long
> does the extra power requirement last?
>
> I recall that some disk drives that I've used in the past have some sort
> of deferred startup: they wouldn't start until the first command
> arrived, or something like that. The idea was to draw less power at the
> instant the machine is turned on. Is this still done? The drives I
> bought came without instructions, just in an anti-static pack.
>
> And another related question: does putting a fan under load (by having
> a filter in front of it, for example) increase power consumption as well
> as slowing the fan down?
>
> Finally, how does the power requirement of a PC interrelate with the
> voltages provided by the PSU? Do these voltages decline even when load
> is well below the nameplate capacity of the PSU, or do they drop only
> when the load approaches the limit, or what? According to my
> calculations, my power supply is loaded at barely a third of its
> nameplate capacity, but the 12V supply is still just a tad below 12V
> most of the time.
>
When the computer starts up, every drive spins up at full speed. This
is the normal procedure to test all the drives at start-up. So all the
combined maximum wattages of each device produces the maximum load of
the PC at startup. However, usually drives go into sleep or standby
modes if they are not being used. So the maximum wattage is only needed
at startup. However, this is when the OS is loading and the hard drive
is very busy. This is when a low power event can cause damage to the files.
Anonymous
a b B Homebuilt system
February 23, 2005 6:51:08 PM

Archived from groups: alt.comp.hardware.pc-homebuilt;,alt.comp.hardware.homebuilt (More info?)

On Tue, 22 Feb 2005 21:30:12 -0600, Last Boy Scout
<eggbtr@ezl.com> wrote:


>When the computer starts up, every drive spins up at full speed. This
>is the normal procedure to test all the drives at start-up. So all the
>combined maximum wattages of each device produces the maximum load of
>the PC at startup.

No, the maximal wattage of the drives, only, is seen for ~
2-4 seconds when the system is first powered on. No other
devices are then at max powe usage unless you count the
surge in charging the capacitors but this is not significant
from a PSU capacity standpoint, so long as it starts up.

>However, usually drives go into sleep or standby
>modes if they are not being used. So the maximum wattage is only needed
>at startup. However, this is when the OS is loading and the hard drive
>is very busy. This is when a low power event can cause damage to the files.

Maximum wattage for drives is not seen after the initial
power-on, spin-up. Just because they're all spinning as OS
loads doesn't means it's a particularly high load. In fact
having a 2nd, 3rd drive spinning would be less load than
having a couple go to sleep and spin down but have the
system in a 100% CPU utilization state (due to modern CPU
deriving power from 12V rail).

Either way, it should never be an issue, the PSU should be
sufficient to power either, any possible power situation the
system can cause. This doesn't necessarily mean the max
possible spec'd draw of ALL components simultaneously as
that may not be possible, but rather the real max potential
plus a fair margin. In a modern high-performance system
this figure is still under 320W, but larger supply may be
needed only because so much power is concentrated on one
(usually 12V) rail.
!