Voc, Isc & Overvoltage Protection

Are Open-Circuit Voltage (Voc) and Short-Circuit Current (Isc) the max output a solar panel can produce?

What is the best way to protect a device from overvoltage?

When it's colder the voltage will increase. This can be calculated with the temperature coefficients on the panel labels.

The best over voltage protection is planning. If the PV input has 150 volt max and your region gets down to -5 in the winter, it's math time. That's how you protect the inverter/charge controller.

Isc is not the max output, it's the maximum output under test conditions. I believe you're supposed to use STC for calculations, and then scale by 125% as the buffer for exceeding those conditions (EG, bright day with zero obstruction of sun + cloud lensing to give you some bonus).

Regarding the temperature planning - can you use the same outdoor design temperature data as HVAC professionals do? And which one do we typically use for PV? Note that for HVAC the consequence of getting it wrong is not as bad as blowing out your PV inputs.

Theoretically speaking, I guess somebody could come up with a voltage-triggered, self resetting smart fuse with FETs rated to sufficient voltage. But then if this thing fails, you have no protection, so you're back to planning.

To prevent over voltage, assemble the panels to stay under 80% of max. 250 volt controller should be fed with Voc of 200v or less.

The

400bird said:

When it's colder the voltage will increase. This can be calculated with the temperature coefficients on the panel labels.

The best over voltage protection is planning. If the PV input has 150 volt max and your region gets down to -5 in the winter, it's math time. That's how you protect the inverter/charge controller.

Click to expand...

The deye 8kw has voc 370vdc(125Vdc 500Vdc) why they use such numbers and the mppt is 125vdc 425 vdc any himt where s the limit

Joehebbo said:

The

The deye 8kw has voc 370vdc(125Vdc 500Vdc) why they use such numbers and the mppt is 125vdc 425 vdc any himt where s the limit

Click to expand...

I don't know how to parse that question. Can you provide the spec sheet or an image of those specifications?

rjolicoeur said:

Are Open-Circuit Voltage (Voc) and Short-Circuit Current (Isc) the max output a solar panel can produce?

What is the best way to protect a device from overvoltage?

Click to expand...

No, Voc is only the max volts at open-circuit, while Isc is the max current (in amps) under short-circuit. Max output would be Vmp and Imp (mp is maximum power).

It might help you to visualize it better by looking at the graph for your panel (showing where the 2 curves for voltage and amperage converge at maximum power point).

Best way to protect from over voltage is to not wire too many panels in series, and take into account coldest temperature (temp coefficient of Voc)...

Use this calculator:

400bird said:

I don't know how to parse that question. Can you provide the spec sheet or an image of those specifications?

Click to expand...

Their s a pic in the comments i attached again data sheet