question

Elimac avatar image

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:

1611334522730.png


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.

mppt smart solarparallel
1611334522730.png (48.2 KiB)
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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 ????

7 Answers
fantail avatar image
fantail answered ·

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


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

diyernh avatar image
diyernh answered ·

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?

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marc-de-montreal avatar image
marc-de-montreal answered ·

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)..

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Elimac avatar image
Elimac answered ·

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.

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marc-de-montreal avatar image
marc-de-montreal answered ·

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

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diyernh avatar image
diyernh answered ·

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.

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marc-de-montreal avatar image
marc-de-montreal answered ·

hi, have you some street lights around of your panels or near a busy street that could explain some parasites effects?!?

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