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Micah Black

Micah Black

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Diode string - 30 of these in series should be reasonable: https://www.digikey.ca/en/products/detail/vishay-general-semiconductor-diodes-division/VS-E4TU2006FP-N3/8269295

Or these: https://www.lcsc.com/product-detail/Diodes-General-Purpose_STMicroelectronics-STTH10LCD06FP_C183000.html

We can connect all the diodes in series, but have a movable connection so that the string length can be adjusted for different numbers of solar panels.

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Current Source: Digital power supply set to 10V, 0.5A
Diode: Generic 10A-rated silicon diode (10 diodes in series).
RSH: 10k 1/8W resistor
RS: 5A glass fuse acting as the series resistance (about 30mOhm resistance).

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I tested with an e-load connected to the output, set in constant voltage mode. Also used remote sense on the e-load to get more accurate voltage measurements (not really needed at these low currents, but it was easy to do). I swept the constant voltage from 0 to 10V while measuring the voltage and current and plotted the following graph:

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These tests clearly show a maximum power point is reached with a smooth curve to the top of it, in contrast to the IV curve of a power supply that has a sharp drop at the MPP. This simulates solar panels very well and can be used to thoroughly test the MPPTs, removing the solar panels from the equation.

More Design Points

  • 1 Diode is roughly 1 or 2 solar cells equivalent depending on forward voltage. We want to be able to do up to 30V output voltage even at low currents, so we need 30/0.7 = 42. We’ll go with 40 diodes since the ones we’re using have slightly higher voltage drop. 20 diodes on each heatsink.

    • Diode spacing: 200mm x 70mm heatsink

      • Diodes about 20mm tall, 10mm wide. 20mm horizontal spacing.

  • Heatsink can dissipate 300W - user should be responsible for obeying this. Safety features could be added in the future (Arduino-controlled MOSFET with a bunch of temperature sensors, voltage sensor, and current sensor).

  • Rshunt: 0.1Ohm should be good. P = I^2 * R = 10*10*0.1 = 10W

  • Rseries: 1k should be good. P = V^2 / R = 30*30 / 1000 = 0.9W

  • Power Input and output connectors (and remote sense)

  • Thermocouple adapter:

    • K-type thermocouple to dual banana jack adapter.