Axpert solar input

**ekkekan** · 2021/01/17, 12:10 PM

I notice the specs refer to say a minimum of 500W input from PV. Is this input purely to operate in the sweat spot?
If only 300W is connected would it still use the 300W available? I just wondered if there is cloud and the PV drops to 300W what output can one expect from the MPPT?

**Monkey-D** · 2021/01/17, 01:51 PM

Ek's nie 'n expert op Axpert nie, maar ek is seker Voc (open circuit voltage) is al minimum wat regtig saak maak om te werk.

Ek verstaan nie hoekom hulle 500W minimum sal spec nie. Kom ons kyk wat ander sê

**fredwb** · 2021/01/17, 02:07 PM

I have also seen specs on one of these units where they say MPPT voltage range 120Vdc to 450Vdc.
My understanding is that it does not accept a voltage lower than 120Vdc and therefore does not operate

**ekkekan** · 2021/01/17, 03:49 PM

Originally Posted by fredwb

I have also seen specs on one of these units where they say MPPT voltage range 120Vdc to 450Vdc.
My understanding is that it does not accept a voltage lower than 120Vdc and therefore does not operate

That to me is understandable but to indicate the V input range as 33-66V with V open circuit as 75V with minimum 500W seems strange.

**faniedup** · 2021/01/17, 03:56 PM

On my 5kW units I have seen solar input as low as 100W being reported. When the sun sets this evening I will try to take a photo of my pi screen

**ekkekan** · 2021/01/18, 05:58 AM

Originally Posted by faniedup

On my 5kW units I have seen solar input as low as 100W being reported. When the sun sets this evening I will try to take a photo of my pi screen

Thanks for your specialist input.

**CeeZee** · 2021/01/21, 08:17 PM

Out on a hunch here, having 2 x 5kw at home...

Standing consumption is I think 75w. Times 24 hrs, adds up on a small installation. Like software, designers sometimes spec not the minimum, but minimum 'viable` system. Taking a cloudy day, a small watt system could leave you in the negative, without switching on a light.

Also, not sure about electronics inside, if constantly running at minimum/off generation, would that hurt it in long run?

Victron small mppt requires 5volts higher than battery to start, but 1v higher to keep running. So, there might be a few design reasons at play as well.

Just thinking..

**ekkekan** · 2021/01/21, 08:25 PM

You are spot on. I got an answer. It is due to the 80W used by the MPPT to operate. They just want to make sure that there is some power to convert. Some other MPPTs do use a lot less power for operation like the Victron mentioned.