Voltage oscillating and trends indication mppt 100/20

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davidezulu asked Dec 31, '22

Voltage oscillating and trends indication mppt 100/20

Hi, I’m testing a new setup with 2 x 180w panel in series connected to an mppt 100/20. VMP 35v, VOC 45v. Have been two overcast day so there is little to no sun at all and I’m noticing a strange behavior of the voltage. It jumps up and down from 20v to 50v, up and down all the time in a matter of seconds. Power at this stage range from 0 to a maximum of 10w as there is no sun. I have a 20w panel here and just to test I connected it to the controller and the voltage is really steady to 17v and the power around 2w. In addition to this the trends are strange, it records the variable voltage from present time back to 2/3 minuts, so the graph is a zig zag up and down, if after 10 minuts I go back and check that point of the graph again seems like the line flattened making an everage of the fluctuating voltage, attached 2 screenshot of the same moment, the first made at present and one made after several time going back to the same exact moment. Any idea? Thanks in advance

MPPT Controllers Solar Panel

585c09f3-7f99-4f0e-8928-7a1c3c244b71.png (292.3 KiB)

74cbaba0-3cc7-4b68-8da5-901c2d71d243.png (318.3 KiB)

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klim8skeptic ♦ commented · Dec 31, 2022 at 09:53 PM

Looks normal for very low solar input. Repeat test when you have decent sun.

Keep an eye on the PV voltage. 2 x 45Voc will give close to the mppt's 100v input limit during frosty weather.

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davidezulu klim8skeptic ♦ commented · Jan 01, 2023 at 09:57 AM

I’ll keep an eye. This is just a temporary setup to make some calculations as I need to charge a 48v 300ah battery and I’m not sure if voltage will be high enough to charge also in low light situation. I got this two 180w for free, I finally would like to use 2 x 380w with vmp34 / voc41 that should give me a bigger margin being that temps here never goes below -5c. I was also thinking going for a 150/35 and use 3 x 380w in series to have a higher voltage, calculation in progress.. I firstly would like to figure out if this big voltage fluctuation is normal or not, waiting for the sun

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davidezulu klim8skeptic ♦ commented · Jan 09, 2023 at 12:55 PM

This is today with decent sun, do you think is normal the zip zag pattern that than flattens out?

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ebce48d0-6529-4a1d-82df-626f394093ee.png (279.2 KiB)

davidezulu klim8skeptic ♦ commented · Jan 09, 2023 at 12:57 PM

Also this

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a120acf8-ce4c-478b-ac83-bfa16f68db5b.png (261.9 KiB)

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Answer 1 · 2023-01-01T07:38:13Z

kevgermany answered · Jan 01, 2023 at 07:38 AM

Putting my retired IT hat on and guessing at how the software is working...

If you look at the first graph, the period of rapid large changes also has the points at much shorter time intervals than before. In the second graph this isn't the case. Looks to me as if the software has averaged out the readings during the time between the graphs.

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davidezulu commented · Jan 01, 2023 at 09:30 AM

Thanks for reply. That was my guessing too, but the graph is also intended to be there to figure out if any problem is present, which I think is the case, unless this is the normal behavior of the MPPT during little light situation trying to find the sweet spot. Any confirmation from some expert on that? If not I just need to wait till the sun comes out and see if the voltage stabilise.

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Answer 2 · 2023-01-09T09:56:13Z

davidezulu answered · Jan 09, 2023 at 09:56 AM

I finally got some decent sun, oscillation is not that big as when there was no sun, but is still present. As you can see than the curve flatten out on the left making the everage of the oscillation into a straight line. Is this a normal behaviour? With the 12v solar panel, voltage was really stable.

971c2278-c8d6-4f47-979f-1cb0804539f7.png (279.2 KiB)

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klim8skeptic ♦ commented · Jan 09, 2023 at 08:40 PM

Glad you eventually got some sun.

The mppt adjusts its power output by varying the current it draws from the array.

A trends graph of the pv voltage and current will show the current being increased and decreased while searching for a higher output. The pv voltage bounces up and down in response to the varying current.

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davidezulu klim8skeptic ♦ commented · Jan 10, 2023 at 12:17 AM

Exactly, finally sun is out :)

So, this little up and down is normal. I was in doubt because when I connect the 12v panel to the 12v battery, the tension coming from the pv was really steady to something around 17v. This up and down only appeared when I connected the two 180w panel to the 12v battery and tested today with the 24v one. I thought MPPT was jumping up and down at the beginning to try finding the sweet spot and than stabilise, it actually do it if I momentarily disconnect the array and reconnect, but than it comes to a point and do little up and down without never really getting completely steady and do little jumps, because of the variating current as explained by you. If it’s normal I quit bothering. Thanks again

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klim8skeptic ♦ davidezulu commented · Jan 10, 2023 at 12:37 AM

Every 10 minutes or so the mppt will do a more thorough "scan" to test the panels power output.

Extend your trends view to an hour to capture that.

Again normal.

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