PSU External Mounting?

[kb1flr]

I have an old e-machine mini tower with a microATX form factor
motherboard. I would like to replace the 120w PSU with something in
the 250w+ range, but the ATX compatible PSU's are much larger than the
existing cases will allow. I could simply get an ATX case and move
everything or mount the PSU eternally and route power in through the
hole left by the departing PSU.

Does anyone see any grounding issues in this plan? Near as I can tell,
all grounding of components in the case tie together and ground is
through the AC ground connected to the PSU. In fact, I don't believe
that, electrically, the PSU must be connected to the case at all,
since the ground is through the ground wire, not the PSU case.

Are my observations incorrect? What are the pitfalls?

Best Regards,
Rick

 

[Dave C.]

I have an old e-machine mini tower with a microATX form factor
motherboard. I would like to replace the 120w PSU with something in
the 250w+ range, but the ATX compatible PSU's are much larger than the
existing cases will allow. I could simply get an ATX case and move
everything or mount the PSU eternally and route power in through the
hole left by the departing PSU.

Does anyone see any grounding issues in this plan? Near as I can tell,
all grounding of components in the case tie together and ground is
through the AC ground connected to the PSU. In fact, I don't believe
that, electrically, the PSU must be connected to the case at all,
since the ground is through the ground wire, not the PSU case.

Are my observations incorrect? What are the pitfalls?

Best Regards,
Rick

Ummmm . . . a new power supply is most of the cost of a case/power supply,
which is usually sold as a set. If your case costs more than your power
supply, you either bought the wrong power supply, or a really expensive
case. My point? Just go to www.mwave.com or your favorite vendor and pick
up a new case AND power supply. The pitfall of mounting the power supply
outside the case is that the fan used to cool the power supply ALSO draws
air through the case. Thus, your system won't be cooled properly unless you
add at least one more case fan, located roughly where the power supply
SHOULD be (and build some kind of custom mount to create the necessary
'vacuum' seal). Plus, most power supplies won't have electrical connectors
long enough to allow mounting the power supply outside the case. Overall,
it looks like a real headache. Just buy a new case and power supply.

BE CAREFUL, though. Pre-built systems often use more than one proprietary
part. If you are determined to still use most of the components from the
E-machine, make SURE they will fit the new case you purchase first. You've
already discovered a problem with a non-standard power supply. Make sure
there are no other nasty surprises in that E-machine BEFORE you purchase a
new case.

I'd probably just start over, anyway. But if you want to salvage what
you've got, a new case and power supply is the way to go, after you've
verified compatibility with all your other components. -Dave

 

[w_tom]

Two different grounds. Chassis ground is different from
motherboard (and power supply black wire) ground. Both
grounds share a single point connection for reasons such as
static electric, avoid ground loops, eliminate software
crashes due to ground noise, etc.

Power supply case must be boned to chassis AND power supply
DC ground (black wires) connected to motherboard.

Another problem might be created. Typically, a power
supply's electrolytic capacitors connect to motherboard by
such short wire as to not create separation problems. But a
long wire connection could put too much separation between
power supply electrolytic and motherboard (increased
inductance). Only way to say, for certain, is an
oscilloscope. Probably will not be a problem if wire remains
short. But demonstrated are two things often not understood
by computer people: different grounds and wire becomes an
electronic component. Question is whether that difference is
significant - a function of wire length and quality of
connectors.

Might be easier to find a new microATX supply; same form
factor now outputs more power. However you know potential
pitfalls. It does not hurt to both try and learn.

 

[netreaper]

http://www.directron.com/matxps.html

Two different grounds. Chassis ground is different from
motherboard (and power supply black wire) ground. Both
grounds share a single point connection for reasons such as
static electric, avoid ground loops, eliminate software
crashes due to ground noise, etc.

Power supply case must be boned to chassis AND power supply
DC ground (black wires) connected to motherboard.

Another problem might be created. Typically, a power
supply's electrolytic capacitors connect to motherboard by
such short wire as to not create separation problems. But a
long wire connection could put too much separation between
power supply electrolytic and motherboard (increased
inductance). Only way to say, for certain, is an
oscilloscope. Probably will not be a problem if wire remains
short. But demonstrated are two things often not understood
by computer people: different grounds and wire becomes an
electronic component. Question is whether that difference is
significant - a function of wire length and quality of
connectors.

Might be easier to find a new microATX supply; same form
factor now outputs more power. However you know potential
pitfalls. It does not hurt to both try and learn.

 

[JT]

I have an old e-machine mini tower with a microATX form factor
motherboard. I would like to replace the 120w PSU with something in
the 250w+ range, but the ATX compatible PSU's are much larger than the
existing cases will allow. I could simply get an ATX case and move
everything or mount the PSU eternally and route power in through the
hole left by the departing PSU.

Does anyone see any grounding issues in this plan? Near as I can tell,
all grounding of components in the case tie together and ground is
through the AC ground connected to the PSU. In fact, I don't believe
that, electrically, the PSU must be connected to the case at all,
since the ground is through the ground wire, not the PSU case.

Are my observations incorrect? What are the pitfalls?

Best Regards,
Rick

Don't forget airflow. If you are stuffing enough into that case that you
need a much bigger power supply, then you will probably have trouble
getting the heat out of that small case. Will have to add a fan to make up
for the loss of the power supply fan. There are also the mechanical and
esthetic considerations of having a mess of wires running into the case.
Cheaper and better to just get a new case that is adequate to the job.

JT