Voltage question

So, now that winter is here I am having to check the PV voltage output every morning and evening to be sure I don’t go over the 150v max.
My observation is this: When I test the voltage without load it shows 143.7v for example. When I connect the array pigtail to the EP500Pro the voltage drops down to say 124v.
My question is this: If the EP500Pro is attached and that taxes the array’s output do I need to worry about hitting 150v coming from the array before or after the “load” is connected. Or is it that with a load there would be no worry about exceeding the 150v? Since the D300 S is not available for purchase I am looking for other stepdown transformers that will do the job of keeping my PV array from putting out more than 150v or another way completely to achieve that goal.

The highest load you will see is before any load is attached (at start up). Once under load you will see lower voltages.

Its a great question. You have to error on the side of caution and count the voltage before the array is fed to the ep500. It may only see that higher voltage briefly until it sags due to it being under load but it sees it none the less. Don’t forget that even a good voltmeter can be off a little. If it gets too close you may want to consider shading a portion of your panels to see it that makes a difference.

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You are correct. Shading a few of the photovoltaic cells with dark plastic will drop some of the output voltage. I did a few test on my panels a few months ago and found this feature. This will prevent the full Voc appearing on any MPPT input but the flip side is that it will reduce the maximum power output.