MPPT voltage and current jumping around late in Absotption stage

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gavin-andrews asked May 3, '20

MPPT voltage and current jumping around late in Absotption stage

We have an EasySolar 48/5000/70-100 with CGX, BMV, lead acid battery bank (460Ah) and 2600W of solar panels. It is a fully off-grid, residential installation.

I noticed a strange issue today. During the low-amperage tail of the absorption cycle, the MPPT voltage and current started to fluctuate rather wildly. I will attach a VRM image of the data, with the issue starting at around 1330hrs. It has been a perfectly clear day, with not a cloud in the sky. The current plot from the inverter indicates there were no unusual loads at the time.

Has anyone else encountered this and what may its significance be?

mppt charging

1588516963261.png (119.1 KiB)

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Answer 1 · 2020-05-03T18:41:31Z

Daniël Boekel (Victron Energy Staff) answered · May 03, 2020 at 06:41 PM

Hi @Gavin Andrews

do you have a screenshot of the power use graph? maybe this is caused by fluctiations in power use?

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gavin-andrews commented · May 04, 2020 at 08:46 AM

The only power output is to the AC system and here is the chart of A.C. use over the same period.

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screenshot-2020-05-04-10-37-25.png (69.6 KiB)

Daniël Boekel (Victron Energy Staff) ♦♦ gavin-andrews commented · May 17, 2020 at 09:05 PM

Hi @Gavin Andrews

ok nothing strange there. can you show:

-charge state of MPPT when this happens? (make a screenshot with both Voltage / Current and MPPT state visible please)

-MPPT settings

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gavin-andrews Daniël Boekel (Victron Energy Staff) ♦♦ commented · May 18, 2020 at 12:02 PM

Hi @Daniël Boekel (Victron Energy Staff)

Please see charts below.

MPPT setiings at the time were:

I have since increased the Tail Current setting to 8,5A, which seems to have reduced the frequency of the issue, but it still occurs.

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mppt-settings-1.png (37.7 KiB)

mppt-settings-2.png (44.4 KiB)

gavin-andrews gavin-andrews commented · May 28, 2020 at 11:45 AM

Hi @Daniël Boekel (Victron Energy Staff)

Please note that this problem persists. I will attach below an image of the issue occurring yesterday during the Float stage. I worry this may harm by batteries.

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Daniël Boekel (Victron Energy Staff) ♦♦ gavin-andrews commented · May 28, 2020 at 01:28 PM

It looks like a load comes on and off, and the resulting drop in voltage makes the MPPT produce more, when the load turns off, it overshoots a bit.

Nothing to worry about.

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gavin-andrews Daniël Boekel (Victron Energy Staff) ♦♦ commented · May 29, 2020 at 01:37 PM

Hi @Daniël Boekel (Victron Energy Staff)

Looking at how it has been behaving the last few days it seems that when the MPPT current is below about 5A, the cycling of the fridge initiates the behaviour. I am surprised that the sudden and erratic voltage and current variations not bad for the battery bank, but thanks for your assistance.

It is playing havoc with my BMV reset points though!

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Answer 2 · 2020-05-16T22:09:00Z

boogymanxxl answered · May 16, 2020 at 10:09 PM

Hallo Gavin, ähnliche Probleme habe ich auch. Nur die Lösung fehlt mir noch.

Vielleicht prüfst Du mal folgende Einstellungen:

VictronConnetAPP> Schweifstrom, ReBulk-Spannung

Eventuell Schweifstrom abschalten und eine hohe ReBulk Spannung wählen. ( 5.2V wird für eine 48V Bank in anderen Foren berichtet)

Frage von mir:

Welche Ladespannungen hast Du im Multi eingestellt (über VEconfig) ?

und welche Ladespannungen hast Du im MPPT eingestellt (über VictronConnectApp) ?

Konntest Du dein Problem lösen...?

LG Lars

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gavin-andrews commented · May 18, 2020 at 11:19 AM

Hi there. Sorry, I don't speak German.

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Answer 3 · 2020-05-29T09:15:46Z

ripper answered · May 29, 2020 at 09:15 AM

I had this several times too. Only found it in the higher bulk or abs voltage. PV Watts go from near zero to near 100% within seconds and back and overshoots by over a volt of desired voltage. That is too much for my AGM batteries I should think. It's an Mppt 100/20 on 24V and there was no fluctuating load attached.

It goes back to doing it when disabling/enabling the maintenance charger setting via ve connect. Only thing helped was taking off all the wires or presumably a night of rest.

I remember playing around with the generator and charger early in the morning while the pv charger was already operational before at least one event. Usually I charge at nighttime so that was a special occasion. Maybe that threw it off hours after?

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