[Cube] Power supply replacement.

[James Deamara]

Hi all.

If anyone is interested, here is what I've come up with so far.

Given a worst case parallel circuit load configuration (that is, one in which
each internal device within the cube forms a parallel circuit where the total current
is divided in proportion to each devices conductance).  Without the need
to power a monitor thru the apple display connector on the video card should
reduce the current requirement of the external power supply by about 4A (as 
noted in the cube specs)...assuming that the DC-to-DC converter board has load 
sensing (and any good, modern DC-to-DC board should). Hence, as long as one
does not need, or ever will need, to use a monitor (apple display) that 
requires power from the video card (as is the case with me) one can
write off 112W (28V x 4A) from the rating of a replacement supply.  Thus, on
the high end, one would probably need a 112W (224W - 112W) power supply to 
run the cube.  Assuming that we would need to "fake out" the DC-to-DC board
by keeping the input voltage at 28V, this translates into a power supply of
112W, 28V @ 4A at the high end.

A low ball estimate might be gathered from the apple specs.  That is, 5W for 
each USB port, 12W for firewire, probably 15-20W for disk and cdrom drives 
(I have lower power laptop drives in my cube), and probably 20-30W
for the processor and MB. That's about 57-72W, which translates into a PS
of 57W, 28V @ 2A or 72W, 28V @ 2.6A at the low end.  Keeping in mind that the
DC-to-DC board probably has load sensing and this figure would probably
be very close to what is needed at a minimum, since all these devices don't
run all at once, all the time.

Since I don't want to spent alot of $$ to keep an aging machine alive, I 
think I'm going to try to rebuild the power supply with the low end estimate.
A good candidate looks like the "Mean Well PS-65-27" switching PS from Jameco Electronics,
(http://www.jameco.com/webapp/wcs/stores/servlet/ProductDisplay?langId=-1&storeId=10001&catalogId=10001&pa=201946&productId=201946).
It even appears that it will fit into the original apple PS enclosure.

I'll keep you posted on any further progress I might have.

James.


----------------------------------------
> From: jdeamara at hotmail.com
> To: cube at listserver.themacintoshguy.com
> Date: Thu, 29 May 2008 01:37:15 +0000
> Subject: [Cube] Power supply replacement.
> 
> 
> Hi All.
> 
> Has anyone out there ever replaced or attempted to replace a cube power supply?  I'm not talking 
> about replacing it with a stock PS off ebay, I mean replacing it with a similarly rated PS (i.e. similar 
> current, voltage, wattage).  Does anyone know approximately how many watts a cube consumes without running 
> an apple monitor thru the video card?  224W (28V at 8A) seems rather steep for a cube without a monitor.
> Looking at the original specs from apple it appears that this higher voltage and current was basically needed
> to run the crt monitor.
> 
> James.
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