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I did not add any load to the 5V or the 3.3V Rails. I only used the 12V. Since this is a Single Rail Power Supply all the 12V wires terminate to a single supply rail.

Your heat up is slower than mine and I believe that we have essentially the same setup. One thing that is a long shot that came up last week concerns the Max PID value set on the EEPROM. It should be set to 255 for max power.

That was a good deal on the Copper Plate. I didn't even think of looking at Amazon.

I ordered the copper plate from amazon, cut it down and machine turned it to make it look better ( it was quite scratched right out of the box ). It was really easy to re calibrate, just a matter of adjusting the z height and rechecking each tower but none of the tower end stops needed adjusting as the entire bed came up the same amount. I haven't really printed anything large yet to check its effects on warping, but i can tell you that now with an IR temp probe I am measuring roughly a 2 degree C difference from center to the outside edge. A huge improvement over stock which could vary up to 20 degrees C.

Ambient temperatures?