Using a second computer case as an external SCSI enclosure

[Guest]

Hi All,

I have an ancient computer that's just collecting dust on my network,
and I'd like to use it as an enclosure to hold (and power) a few SCSI
devices, one DVD burner and two hard drives. It will be connected
to my primary system with proper cabling (an interior-exterior SCSI
cable adapter, etc), and the devices will be run off the exterior SCSI
port on the controller in my primary system.

My question has to to with the Sparkle (SPI) FSP300-60GT power
supply in this secondary machine. I know these supplies require a
minimum load on certain rails, although I have no idea which rails,
and what voltage is required on each.

If I use this supply to run the three SCSI devices, but don't connect the
motherboard or any other power leads, will this be enough to satisfy
its minimum load requirements?

I hope I've described my question clearly, and I appreciate any help
or info.

Thanks,

Jeff

 

[Baron]

Hi All,

I have an ancient computer that's just collecting dust on my network,
and I'd like to use it as an enclosure to hold (and power) a few SCSI
devices, one DVD burner and two hard drives. It will be connected
to my primary system with proper cabling (an interior-exterior SCSI
cable adapter, etc), and the devices will be run off the exterior SCSI
port on the controller in my primary system.

My question has to to with the Sparkle (SPI) FSP300-60GT power
supply in this secondary machine. I know these supplies require a
minimum load on certain rails, although I have no idea which rails,
and what voltage is required on each.

If I use this supply to run the three SCSI devices, but don't connect
the motherboard or any other power leads, will this be enough to
satisfy its minimum load requirements?

I hope I've described my question clearly, and I appreciate any help
or info.

Thanks,

Jeff

Short answer. Yes ! You will need to ground the PS (Green wire) to turn
it on. Or any older AT PSU with a real mains switch. In which case
you will need to load the 5V to draw about an amp.

 

[Guest]

Short answer. Yes ! You will need to ground the PS (Green wire) to turn
it on. Or any older AT PSU with a real mains switch. In which case
you will need to load the 5V to draw about an amp.

Thanks Baron. I found specs for the Sparkle supply, and it lists
mimimum loads for the +5V and +3.3V rails (1.5A and 0.2A
respectively). Minimum for all other rails is 0.0V.

http://www.powrtech.com/new_page_47.htm

Is there a way to know which rails my three devices are going to
use? I seem to remember reading that +12V is standard for most
hard disks. How would I go about loading the 3.3 and 5V rails?
Is it easiest to just connect the motherboard connector? I'd rather
not do that if possible, because it generates a lot of fan noise for
its cpu and other fans.

Thanks again.

Jeff

 

[Paul]

Thanks Baron. I found specs for the Sparkle supply, and it lists
mimimum loads for the +5V and +3.3V rails (1.5A and 0.2A
respectively). Minimum for all other rails is 0.0V.

http://www.powrtech.com/new_page_47.htm

Is there a way to know which rails my three devices are going to
use? I seem to remember reading that +12V is standard for most
hard disks. How would I go about loading the 3.3 and 5V rails?
Is it easiest to just connect the motherboard connector? I'd rather
not do that if possible, because it generates a lot of fan noise for
its cpu and other fans.

Thanks again.

Jeff

A hard drive draws from +12V (motor) and +5V (logic). The logic board
may draw 5V @ 1A. You can look up the specs for each hard drive,
on the manufacturer's web site. To be safe, you could use twice as
many drives, as are needed to guarantee the minimum loading.

These are the numbers I use, which change with time as more efficient
technologies are introduced. These numbers are now on the high side.
Modern drives could have lower numbers.

Hard drive - 12V @ 0.6A and 5V @ 1A, 12W total. Higher 12V current
for the first ten seconds. Perhaps 12V @ 2.5A for the
first ten seconds of spinup.

Optical drive - 12V @ 1.5A and 5V @ 1.5A. That is a "boiler plate" value
used by manufacturers, when they don't want to tell you
the truth. My current optical drive uses 12V @ 1.0A
measured. If the power consumption was consistently high,
the CD/DVD casing would get warm, and it doesn't seem to.

Your drives should not be drawing power from the 3.3V rail. You would
need to connect a small dummy load, to meet that requirement.

This 3 ohm power resistor, would draw 3.3V/3ohm = 1.1 amps.
3.3V * 1.1A = 3.63W. Power resistors like this, have ceramic housings
and can heat up to high temperature when operated at full power.
Forced air cooling (locate near your cooling fan), can help
keep the resistor at a reasonable temperature. I use power
resistors in my load box, for testing new PSUs. I use an
80mm fan to keep my collection of resistors (multiple ones
per rail) at a reasonable temperature. If you connect this
resistor to your 3.3V rail and to GND, it will draw 1.1 amps
from the rail.

http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=L25J3R0E-ND

This style can be bolted to a heatsink. Larger power rating
resistors are possible. If you have a surplus electronics store
in town, they may stock huge "clunkers" suitable for building
larger loads. Someone at work built such a device, using
parts from a surplus operation down the road from us.

http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=KAL25010FB-ND

The 3.3V wires are on the main power supply connector. So you need
to connect your "dummy load" to the main connector.

If you need to make a harness, for your load resistors and your switch to
ground the PS_ON# wire, you can purchase an ATX extension cable, which
will give you a power supply connector and wires. Hack the cable to bits,
and use some solder to connect the resistor to the appropriate wires.
By using solder, the thing won't come undone at an inopportune moment.

This resistor from Radio Shack, is 10 ohms and is rated for 10W
dissipation. So you don't need to go to Digikey to get a solution.
3.3V/10ohm = 0.33A, which is just a bit more than the 0.2A specified.
3.3V * 0.33A = about one watt, so this one isn't going to run quite
as warm. It all depends on whether you want to draw a bit more than
the spec or not. You can put multiple resistors in parallel, and
each would draw 0.33A. Using series/parallel arrays of resistors,
is one way of spreading the heat when building dummy loads.

http://www.radioshack.com/product/index.jsp?productId=2062291

This isn't that good a reference, and I throw this in more as a joke...
Nobody wants to see an integral symbol, their first day on the job.

http://en.wikipedia.org/wiki/Ohms_law

This is more what I was looking for.

http://physics.bu.edu/py106/notes/Circuits.html

For ATX connector pinout info, you can try these. The first is for
24 pin supplies, the second and third are for 20 pin ones. The
third spec is from the days, when -5V was still present on the
connector. I haven't tested these links lately, to see if they're
still valid.

http://www.formfactors.org/developer/specs/ATX12V_PSDG_2_2_public_br2.pdf
http://www.formfactors.org/developer/specs/atx/ATX12V_1_3dg.pdf
http://web.archive.org/web/20030424...org/developer/specs/atx/ATX_ATX12V_PS_1_1.pdf

Paul

 

[Paul]

Also, we don't know what happens when the minimum load is not met.
In principle, the regulation could be off (so the rails are more
than +/-5% off the normal value). The supply probably doesn't go
crazy. If it was me, I'd search for a supply without a minimum
stated.

http://c1.neweggimages.com/NeweggImage/productimage/17-194-031-13.jpg

http://www.enermaxusa.com/catalog/product_info.php?cPath=21_55&products_id=150

Paul

 

[Guest]

Also, we don't know what happens when the minimum load is not met.
In principle, the regulation could be off (so the rails are more
than +/-5% off the normal value). The supply probably doesn't go
crazy. If it was me, I'd search for a supply without a minimum
stated.

http://c1.neweggimages.com/NeweggImage/productimage/17-194-031-13.jpg

http://www.enermaxusa.com/catalog/product_info.php?cPath=21_55&products_id=150

Thanks Paul & all. I'm trying to do this on the cheap, using parts I
already have. I can pick up a used SCSI enclosure on eBay for
$20+ shipping, that would include a dedicated PS, but I figger why
spend the money if I can avoid it?

Specs for the Sparkle give a combined wattage rating for both the
5V + 3.3V rails.. Does that mean a load present on one of those
rails will result in a shared load on both? I'm hoping this will satisfy
the 0.2V minimum for 3.3V.

Jeff

 

[Guest]

Thanks Paul & all. I'm trying to do this on the cheap, using parts I
already have. I can pick up a used SCSI enclosure on eBay for
$20+ shipping, that would include a dedicated PS, but I figger why
spend the money if I can avoid it?

Specs for the Sparkle give a combined wattage rating for both the
5V + 3.3V rails.. Does that mean a load present on one of those
rails will result in a shared load on both? I'm hoping this will satisfy
the 0.2V minimum for 3.3V.

Sorry, that should have been 0.2A, not 0.2V.

 

[Paul]

Thanks Paul & all. I'm trying to do this on the cheap, using parts I
already have. I can pick up a used SCSI enclosure on eBay for
$20+ shipping, that would include a dedicated PS, but I figger why
spend the money if I can avoid it?

Specs for the Sparkle give a combined wattage rating for both the
5V + 3.3V rails.. Does that mean a load present on one of those
rails will result in a shared load on both? I'm hoping this will satisfy
the 0.2V minimum for 3.3V.

Jeff

It could be interpreted to mean a common transformer is used for
both rails. Or the rectifiers are bolted to a common heat sinking
plate. Some resource must be shared in such a way, as to cap the
overall combined total.

The minimum load of 0.2A is intended to make the output rail
meet 3.3V +/- 5%. Without the load, it is possible the rail could
be lower or higher than that. Since you're not using 3.3V, there
is no direct concern. Of indirect interest though, would be
if the 3.3V regulation is a primary determinant of the other
output voltages, in which case, it could cause an error in
the 5V rail if the minimum load is not present.

Xbitlabs sometimes runs a cross regulation set of curves for
reviewed power supplies. The red portion of the graphs
here, show what happens when one rail or pair of rails is
pushed to the max (asymmetric loading). Some supplies show
better cross regulation characteristics than others. If the
supply is in the red, it doesn't cause the computer to stop running,
but for devices that are sensitive to correct voltage (like
the 12V motor supply on the hard drive), sometimes the
hard drive will start clicking in response to the low
voltage. It means the motor or voice coil actuator are
having trouble with the voltage being on the low side.

http://www.xbitlabs.com/articles/coolers/display/psu-methodology_13.html

Another graph of cross regulation. Every supply is different.

http://www.xbitlabs.com/articles/coolers/display/powerful-psu_11.html

The Truepower has individual remote sense signals, and it helps a bit.
I don't know what the transformer scheme is here. It might still be shared.

http://www.xbitlabs.com/articles/coolers/display/powerful-psu_5.html

The reason this happens, is on a cheap supply, there is only
one control on the primary side of the supply. The
secondary side consists of multiple windings on a common
transformer. If one output is heavily loaded, the feedback
loop can tell the primary "more power please". The result
is, that two rails have abnormally high voltage, while
the loaded rail may be nominal or a bit low. The supply
tries its best, to balance the error on the rails, but in
some situations, it may fail to meet the overall limits
defined in the appropriate version of ATX spec.

If a power supply uses independent circuits for everything,
there is no cross regulation problem at all. That is not
typically how they build them. Sample (really old)
schematic here of one with lots of sharing.

http://www.pavouk.org/hw/en_atxps.html

In that diagram, transformer T2 isolates the low voltage controller
from the high voltage transistors on the primary. You can see
that output transformer T3 is shared, and the turns ratio
determines the relationship of the output voltages. The
rectifiers on the output side, convert the high frequency
AC from T3, into pulsing DC, which is filtered by the output
caps. The bit that doesn't get filtered, is the ripple on
the output. If the ripple amplitude is too high, it can
cause logic failures (and this is something best checked
with an oscilloscope - a multimeter wouldn't really help).
So it is possible for a power supply to be meeting the
DC requirements, but fail due to being "too noisy" on the
rails.

http://www.xbitlabs.com/images/other/powerful-psu/p7.gif

Paul

 

[firebird-jmw]

Hi All,

I have an ancient computer that's just collecting dust on my network,
and I'd like to use it as an enclosure to hold (and power) a few SCSI
devices, one DVD burner and two hard drives. It will be connected
to my primary system with proper cabling (an interior-exterior SCSI
cable adapter, etc), and the devices will be run off the exterior SCSI
port on the controller in my primary system.

My question has to to with the Sparkle (SPI) FSP300-60GT power
supply in this secondary machine. I know these supplies require a
minimum load on certain rails, although I have no idea which rails,
and what voltage is required on each.

If I use this supply to run the three SCSI devices, but don't connect the
motherboard or any other power leads, will this be enough to satisfy
its minimum load requirements?

I hope I've described my question clearly, and I appreciate any help
or info.

Thanks,

Jeff

Either MCM (MCMinOne.com) or newegg has a power supply test load for a
couple of bucks. Attach it to the 20 or 24 pin mainboard connector and
it will take care of the problem.

 

[Baron]

They are not meant to be used on a continuous basis. They get too
hot
to touch in under a minute, and every one I've seen says not to use
for more than one minute at a time.

I agree ! You could cook eggs on my 120w test load within a few
minutes... Great on a cold morning though.

 

[Eeyore]

Hi All,

I have an ancient computer that's just collecting dust on my network,
and I'd like to use it as an enclosure to hold (and power) a few SCSI
devices, one DVD burner and two hard drives. It will be connected
to my primary system with proper cabling (an interior-exterior SCSI
cable adapter, etc), and the devices will be run off the exterior SCSI
port on the controller in my primary system.

My question has to to with the Sparkle (SPI) FSP300-60GT power
supply in this secondary machine. I know these supplies require a
minimum load on certain rails, although I have no idea which rails,
and what voltage is required on each.

Chances are that the 5V and 12V loads will be fine.

If I use this supply to run the three SCSI devices, but don't connect the
motherboard or any other power leads, will this be enough to satisfy
its minimum load requirements?

I hope I've described my question clearly, and I appreciate any help
or info.

Yes, it's been done before. Just a storage subsystem.

Graham