# Strange DC at MPPT input at night

My 150/70 is having a strange DC at its input during some nights, not all. Here's an example:

Almost 18V at input. Suddenly around 23.56 it has gone to zero but it came again as you can see.

This MPPT is a part of a bluetooth parallel network, with 2 more 250/60 in which none of them shows this behavior.

What could be this about? It is connected to 3 strings, it's chassis is grounded, as well as the panels frames.

Running fw version 1.54.

1611334522730.png (48.2 KiB)
1 comment

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

Have you measured the PV input voltage at the regulator at those times with a Volt meter. If the volt meter shows the same value then it has to be correct ????

also check if it is a full moon on a clear night

1 comment

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

ooh yes, a full moon can also do that and with some clouds, have stranges on/off PV output!! ..super idea fantail!!

That's not a negative amperage, is it? I thought it was zero per the graph, but could be a bad diode on the panel, discharging the battery and heating the panel?

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

haha.. after to have saw the « interstellar » movie, each time i see something strange things, i try to find if there are any kind of ghosts hidden codes!! ..for to kill the street light static effect on my first 18v panel (was around 15-17v static because a street light is near and switch off by overheat randomly doing strange Morse code look like), i has put 1 kilo-ohms (1 watt) in parallel.. since, the night voltage still below 2 volts.. if you short your panel with a ampere meter (during the night), the value (in my case 10 to 12ma) tell how much current you need to kill (1k = 18ma was enough to me)..

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

Hello,

I did not see this again, so I could'nt test further. I don't think is outside noise, it seems internally generated, but I can't be sure at the moment. A high value resistor on PV side seems an interesting idea to me, maybe it can pull the line down and override this noise, wherever it is coming from.

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

so 2 things, can you live with it or put a load resistance?

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

You have almost no amps. It may just be some small fluctuations in volts, but no current. Some of the cheaper DAQ systems tell you to put a high resistance resistor across it to stop reading the noise.

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.