How close dare I go towards my Solar Controller's max Voc? (1 Viewer)

[Lizbiebrowne]

Looking to fit a 400 W solar panel to my van and connecting it to my Voltronic MPP 430. The panel has a Voc of 46.7 V and the MPP 430 specifications say the maximum Voc should be 50 V. Is this too close for comfort? There another 400 W panel with a Voc of 37 V and I wonder if it would be more sensible to use this one.

 

[autorouter]

The panels will have the maximum voltage when the batteries are full and the panels are cold, which is most likely on a winter afternoon. If the panel is flat on the roof (ie not tilted) then the winter sun won't develop the panels full voltage. However I still think it's a bit close to the limit. Best to ask Raul, I think. The controller's maximum voltage is a hard limit, not to be exceeded. Unlike the amps limit, where the controller just wastes power without damage if the amps limit is exceeded.

 

[Raul]

At -10C in a morning, with a temp coefficient of 0.3% per deg C your panel will see 53v plus. Look at your panel data, it should give a temperature coefficient. The bigger the coefficient, the larger the voltage swing on cold. The stc data is at 25C.

 

[Lizbiebrowne]

The temperature coefficient is negative, -0.27%/ C. Does that change the analysis?

 

[Raul]

The temperature coefficient is negative, -0.27%/ C. Does that change the analysis?

Yes a bit, it will be 51.113v at -10C. So from -8 down you risk burning the controller.

The 46.7voc is at 25C deg.

0.27x 35C= 9.45% 46.7v + 9.45%= 51.113voc at -10C

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[autorouter]

The temperature coefficient is negative, -0.27%/ C. Does that change the analysis?

It's all relative to the voltage at 25°C. Above 25°C the voltage decreases. Below 25°C the voltage increases. That's because the temperature change from 25°C is negative, the temperature coefficient is negative, so when multiplied that makes a positive voltage change.

 

[Lizbiebrowne]

Yes a bit, it will be 51.113v at -10C. So from -8 down you risk burning the controller.

The 46.7voc is at 25C deg.

0.27x 35C= 9.45% 46.7v + 9.45%= 51.113voc at -10C

It's all relative to the voltage at 25°C. Above 25°C the voltage decreases. Below 25°C the voltage increases. That's because the temperature change from 25°C is negative, the temperature coefficient is negative, so when multiplied that makes a positive voltage change.

Thanks Raul and autorouter for the calculations and explanations, I'm glad I asked the question. I will buy the one with the lower Voc: with a Voc of 37.2 C and a temperature coefficient of -0.275%/ C I'm going to have to find some extreme conditions to damage the controller, around -68 C I calculate

 

[Ridgeway]

Plan B: upgrade your controller and sell the old one ?