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Tested the MOSFET (See reference below) and replaced MOSFET and everything seems to be working now. 

This unit has a 150W limit! So, if you are using 40V, the max current you should draw would be:

P=IV

I=P/V

I=150/40

I = 3.75A

Why did it Break?

Probably because I hadn't reset the knobs controlling the current to zero resistance before connecting to battery.

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