MPPT constantly changing charge status

Q&A and troubleshooting
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1

Dear All,

I have a self (re)built Lion NMC 3S2P with ca. 70Ah Battery-pack, which voltages level ranges between 3x3,2 V= 9,6 V Min up to 3x 4,0V = 12,0V max. to prolong service life.
I use for this project a DALY Smart BMS 100A rating (I do use it only up to 50A max current draw), which seems to be Okay. I do have no issues so far.

My problem:
I do own a MPPT 100/30 SmartSolar, which works well with ´high´ voltage Solar Panels like, 60Cell or more, BUT, if I connect it to the so called ´12 Volt´ or ´24Volt´ Panels than comes in the Problem:
If I leave the Battery charge current ´unlimited´,
→ than the MPPT starts going in BULK, as soon the panel voltage is about +5V battery voltage…
→ Than the MPPT find its Maximum powerpoint (MPP),… BUT
→ Than often the PV Panel Voltage drops thus far, that the MPPT changes to the ´Off´-mode, as (I believe) the panel voltage drops to ca. the battery voltage, and sure, that won´t work…

I have observed the behaviour of the MPPT since a long time and I am doing experiments all the time, but I believe the MPPT Tracking algorithm should maybe be improved to avoid situations I do have? Or do I really still overlook something? Or is this technically not possible to modify the algorithm (by Victron) in a way to avoid my issue??

Depending on the wether conditions, I am able to set a current limit in between 2A and 7A for a certain small panel I do have (Voc ca. 20V), and than the MPPT runs without problem, as the panel voltage doesn´t drop too much. but like during sunset, the MPPT is again trying to find its MPP and continuously changes its charge state from BULK to OFF and vice-versa and like this I am not able to efficiently charge my 11V nominal battery.

As I wrote, If have tested this now with several (4) panels and it only happens with my 2 smaller panels (about 20 Voc). I also eliminated a problem with the connectors/ plugs by cutting them off and the use of other cables. By measuring with the multimeter also everything looked fine.

I believe, the MPPT algoritmth should use the Battery charge voltage (absorption and float) set by the user and therefore should adapt the charge algorithm to go no NEVER underneath the battery voltage +1V for the Panel circuit while searching for the MPP in case the MPPT is being able to generate power staying above these voltage setting/ limit, which it usually is.

Does someone exactly know how the charge algorithm of these MPPTs works? As I strongly believe the MPPT is not taking the battery charge voltage setting into account while searching for the maximum power point and thus trying to push the Amps pumped into the battery while ´forgetting´ about the ´allowed and possible´ charging voltages. What do you think about my hypothesis?

attached a video for better understanding:

photo_2024-12-20_16-14-34
photo_2024-12-20_16-14-34960×1280 354 KB

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Put the panels in series ?

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hi @Ludo , thank you for your comment.

Yes true, I tried that as well and indeed that solves the issue as well. As by doing this the Voc/Vmpp increases/ doubles.

Putting in parallel does not make a difference (just for information).

But still am not happy with this behaviour, in case I want to have just 1 panel connected (because I use this power-bank for remote work locations and sometimes I just put 1 panel on top of the roof of my car temporarily)

Any other thoughts though?, As you see in my screen recording, the panel is actually able to produce about 80Watts, but it looks like the MPPT is seeking for a higher power output and than reaches (I think) a too low PV-voltage and goes in Off-state for about 10 seconds and start all over…

4

Take a pwm solar charger…

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Thats is what I was thinking of doing as well, but my stecca pr1515, did not allow me to set a max. Voltage limit of 12.0V only ;(

Sure in terms of testing, I could connect it when the battery has a low SOC and to see how it behaves. But at some point the BMS will disconnect as a safety measure…

Do you know more about the MPPT algorithm? I have to search the old community site, where I found a similar topic where someone had an old and a new mppt and for that person the old one performed better than the new one. That has been another reason for me to think its a algorithm issue, I believe that has not been solved either.

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I have a silky litte 20W panel on a 75\15. It runs fine.
Are you sure the panel, wiring and connections are ok?

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Hi @lxonline, thanx for your reply.

That´s indeed quite cool that such a little panel works. good to know.
Are you for my curiosity also able to make a screen recording with your phone, how I did? just to see, how the MPPT finds it MPP with the respective voltages (PV and Bat)?

I am quite sure, all cabling is correct and working well. And If I put another panel in series it seems to work also, but I did not make screen-recording of that setup so far.
Is there another way of checking the Solar panel, maybe there is somehow a bad contact. Voc is always there, but I should maybe measure the Shortcircuit amps (I believe actually all cable as well the panel is behaving well, because if the little panel works alone, I need to downgrade the Charge amps… but if there is another panel in series, I can go higher or even ´unlimited´ with the charge setting; but let me confirm with a screen-recording)

I didn´t realize before to mention it, but the MPPT was ´broken´ by a friend of mine, who connected it the wrong way around (Battery Plus & Minus the other way around :face_with_peeking_eye:).

As I never trough something away before attempting to repair it, I got it fixed by replacing the midi-fuse and believe nothing else was broken as with a bigger panel it is performing perfect without noticing any issues as well.

BR,
Ruben

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I have a problem with 100|50 attached to 12V Sonnenschein gel cells, when they are near the end of charge and they are below say 6A, and something destabilizes the charge, like a toaster, so there is a sudden rise past 14.7V and the charger panics and turns off, so as not to damage the battery. But it turns right off, and then the battery voltage sinks back down again, so when the charger comes back on, it comes back hard, and overshoots and panics again. My solution is to have a lower charge voltage and higher float voltages. Also I have an Epever MPPT that is more stable and slooooow than Victrons. It performs better in cloudy weather, because it picks 36W and just stays there, whereas the Victrons keep changing their mind, and only get half the power of the Epever. I have a Tracer AN series on my vegie patch pump, and that seems OK, but needs the MT50 to program it. Your cheapest solution might be to set a current limit below where it starts to panic. so the panel voltage stays high. Never let it get to 83W

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dear @Astrayan ,

what voltage settings have you set when this 14,7 fluctuating battery voltage level arises?
it is indeed weird, that for some reason the Victron MPPT isn´t able to efficiently harvest the energy potential… Dnd regarding your voltage peak, could that maybe be because of a weak battery and that therefore an certain voltage ´spike´ arises? . Although I would also think that if you have set your Charge voltages, than the Victron MPPT should limit any chargevoltage up to that voltage avoiding any ´shoot´-out´. Or might the MPPT not being fast enough to avoid this ´shoot-out (due to a bad or evtenutally no battery for instance)?

I am still hoping someone could confirm the way how the MPPT´s are searching for their MPP and what ´minimum´ voltage they uses. It should offcoarse be above the battery voltage or even egual or above the charge voltages set by the user, and quite sure Victron programmed it somehow like this as well. Just wondering if there could be firmware bugs or similar, or that this ´error´ could be excluded by 100% …?´

Yesterday I observed my charging behaviour and I did not realize any issue… :face_with_raised_eyebrow:
Now I am still unsure if it is because of low Sun Radiaton (thus the PV-side current was not going above 3,5Amps, and Battery current about 5Amps) or that I do have an inconsistent bad connection somewhere (again) which ´coincidantly´ worked yesterday well. I also Short circuited my Panel and that resulted in about 3,5-4Amp max. without interruption.

I will eliminate any PV-connectors for the testing purpose to see if that resolves my issues. Might be that I only did that for 1 panel and not for the one I am using right now. I will report back. :wink:

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I’m using gel cells that really block current when some of the cells become fully charged. Even though the battery is 1200AH, some of the cells can be 2.5V with only 0.7A going through them. Flooded cells might require 2A to keep the voltage up. It still shouldnt matter, because the 100|50 should be able to do a car battery. I have absorption set to 14.2, and float at 13.8

11

Just a quick post, that I was not able to reproduce my problem as initially described.

I am still waiting for a day where I have time and whereas the sun delivers enough power in order to do my final tests (aka without any MC4 connector in between the MPPT and the Solarpanel). Keep you posted.