question

Use Voc or Vmpp value for design of panel output strings to MPPT 250|100.

I am an amateur designer just wanting to understand

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Voc and make sure you also take into account the increase in voltage as temperatures drop. The MPPT input voltage ratings are a hard limit and damage will happen if you exceed it. Isc is also critical.

Best is to do the calculations using the calculator at Victronenergy.com

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Grateful for the answer. My understanding was that VOC was measured with no load in the circuit. In the design the panel strings are connected to 100 metres 10AWG copper cable with two separate islation switches before connection to MPPT 250|100. The VOC of the panels = 5 X 49.75v yet the VMpp is 5 X 41.8v. Is this complete circuit only measured as OPEN?

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Voc stands for Voltage in open circuit. So yes. It represents the highest no load voltage the panels generate under standard conditions, one of which is 25C (77F). When batteries are fully charged, the MPPT shuts down the load on the panels. As far as the panels are concerned, it looks like an open circuit, so voltage rises because there's no load. But the MPPT still sees the panel voltage on its input terminals.

(Vmp or Vmpp is Voltage at maximum power.)

With these 5 panels in your strings, you're on the limit for the controller. When temperatures drop, you're very likely to exceed it and blow the controller. Please use the calculator to correct your design.

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kevgermany ♦♦ ·
Thank you for the information.
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