question

davidezulu avatar image
davidezulu asked

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


632f5569-c74b-4b35-a35a-d667e77e2701.png
585c09f3-7f99-4f0e-8928-7a1c3c244b71.png

MPPT ControllersSolar Panel
585c09f3-7f99-4f0e-8928-7a1c3c244b71.png (292.3 KiB)
74cbaba0-3cc7-4b68-8da5-901c2d71d243.png (318.3 KiB)
4 comments
2 |3000
Toggle Comment visibility. Current Visibility: Viewable by all users

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

klim8skeptic avatar image klim8skeptic ♦ commented ·
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.

0 Likes 0 ·
davidezulu avatar image davidezulu klim8skeptic ♦ commented ·
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


0 Likes 0 ·
davidezulu avatar image davidezulu klim8skeptic ♦ commented ·

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

0 Likes 0 ·
ebce48d0-6529-4a1d-82df-626f394093ee.png (279.2 KiB)
davidezulu avatar image davidezulu klim8skeptic ♦ commented ·

Also this


0 Likes 0 ·
a120acf8-ce4c-478b-ac83-bfa16f68db5b.png (261.9 KiB)
2 Answers
kevgermany avatar image
kevgermany answered ·

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.

1 comment
2 |3000
Toggle Comment visibility. Current Visibility: Viewable by all users

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

davidezulu avatar image davidezulu commented ·
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.
0 Likes 0 ·
davidezulu avatar image
davidezulu answered ·



971c2278-c8d6-4f47-979f-1cb0804539f7.png


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)
3 comments
2 |3000
Toggle Comment visibility. Current Visibility: Viewable by all users

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

klim8skeptic avatar image klim8skeptic ♦ commented ·

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.

0 Likes 0 ·
davidezulu avatar image davidezulu klim8skeptic ♦ commented ·
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
0 Likes 0 ·
klim8skeptic avatar image klim8skeptic ♦ davidezulu commented ·
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.

0 Likes 0 ·

Related Resources

MPPT Product Page

MPPT Error codes

MPPT 150/60 up to 250/70 Manual

Additional resources still need to be added for this topic