The Nomura MPPTs evaluated by the team have a fairly unique design compared to most other solar car MPPTs. Instead of having each MPPT designed to output the full battery pack voltage, Nomura MPPTs are designed to only output up to 37 V and must be stacked in series on their output sides in order to charge the battery. This configuration is advantageous because it enables each MPPT to have a smaller string of PV cells on its input side, making the entire array significantly more robust against uneven lighting. Moreover, due to the large surface area of the SunPower cells being used on MSXII, the total stackable cell voltage for the entire car is quite low and would only support around 2 strings for traditional MPPTs.
However, this also posed some interesting and potentially confusing questions about how MPPTs in a "stack" coordinate together to output the correct pack voltage. After some testing with 3 Nomura MPPTs, this article has been written to document our best understanding of how they work to hopefully reduce confusion about these devices moving forward.
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