XMT 300 PC Main Power Unit

The XMT 300 PC power supply features a bright blue enclosure that highlights Miller’s The Power of Blue slogan.  Did I mention this thing is huge!  The unit is designed to sit on the floor and that is where most people will leave it.


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The fiberglass case is divided into an upper and lower half that bolts together in the middle.  Miller thoughtfully included two industrial-grade carrying handles on top.  I was able to move the unit around by myself and set it up on the desk for our photo shoot but since it weighs a full 80 lbs you might want to ask for help when moving this bad-boy.


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The main power On-Off switch is located in the upper right corner on the front panel for easy access.  The front panel contains several controls not normally seen on a PC power supply.  The two dials in the middle allow tweaking the power supply’s output voltage and current.  The main +12V rail output voltage can be adjusted from 10 to 16 volts using the smaller of the two dials on the left.  That is a huge span!  I strongly suggest you set the output voltage between 12.0V and 12.5V.  Anything below 11.0V or above 13.0V could potentially damage your PC.  The extreme adjustments are for advanced users only and are normally used in conjunction with cryogenic cooling (liquid Nitrogen or dry ice/acetone).


The larger dial in the middle allows setting an upper current limit for the power supply.  This is a safety feature, which can help minimize property loss and casualties should something go wrong in the wiring or components inside your PC.  Since the Miller PSU incorporates a single, monster +12V rail, there is no 240 VA limit as there are with many of the typical high capacity PC power supplies that have multiple +12V outputs.  The original idea behind having multiple +12V outputs was to limit the potential energy available on any user accessible components to 240 VA (12V x 20A).  Doing so will minimize the size of the fireball and the amount of molten material that could be ejected from an arc-flash event if a short circuit happened to occur.  I wouldn’t want to be in the immediate area if the Miller XMT 300 PC’s full 375A output were somehow discharged instantaneously across a dead short!


I have to admit, some of these new high-output power supplies make me a little nervous when I’m testing them at their full rated capacity.  I had a 1kW unit blow up on me several months ago at full load.  Now I wear safety glasses and keep a fire extinguisher close at hand during testing — I’m serious.


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Looking around to the back of the big Miller XMT 300 PC power supply we see a very heavy duty power cord and numerous louvers for air cooling the internal components.  The XMT 300 PC is designed to operate from either 3-phase or 1-phase AC power.  This is good as very few if any residential customers will have 3-phase power in their homes or small offices.  I used a 1-phase dryer outlet in my basement that is rated for 30A at 240 VAC for testing.


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