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cdn4runnersolar asked

What is causing irregular wattage fluctuation in Float charge – MPPT 100/20?

Firstly, here is my solar setup on my Toyota 4Runner:

1 - Victron MPPT 100/20 charge controller (firmware 1.59) with 2, 12V cigarette lighter connections to the “Load Output”. The MPPT is networked to a Victron SmartShunt

1 - Victron SmartShunt 500 amp (firmware 4.08), networked to MPPT to provide battery voltage and temperature

1 – Renogy Eclipse 100W solar panel permanently mounted onto my roof, specs: Open-Circuit Voltage (Voc): 21.2V, Short-Circuit Current (Isc): 6.10A, Optimum Operating Voltage (Vmp): 17.7V, Optimum Operating Current (Imp): 5.70A

1 – 20 amp inline fuse at the solar panel

1 – FullRiver Battery, 105 amp hour, AGM battery

1 – Dual dash camera that is powered/wired directly to the AGM battery (it does not connect to the Load Output of the MPPT), which draws 360 mA or 0.36 amps. It’s constantly on, in “parking mode”.

I have used the “user defined” and “advanced settings” for the battery charging parameters in the MPPT, following FullRiver’s charging parameters perfectly.

Now here is the issue which is sporadic and very puzzling. When in direct sunlight, without any draw from the Load Output (i.e. my fridge is unplugged/off), but a small 0.36 amp draw from the dash camera directly connected to the battery, the MPPT will go through its proper cycle of “bulk”, “absorption” and then “float” charging. I’ve noticed that randomly during the float charge, it will go from 15/16/17/18 watts, down to 1/2/0, then back up within 1-2 seconds. Also the amps will fluctuate 0.5 – 1.2 down to 0. Of course the battery voltage will jump (slightly) up and down during this time. The SmartShunt is reading at a 97% state of charge. Then after some time, the MPPT will settle in, with a steady (maybe fluctuate 1 or 2 watts) watt and amp input. But then goes back into the fluctuations.

When I connect a draw to the Load Output, i.e. turn on my fridge (draws between 35 – 45 watts), the MPPT will automatically compensate for the draw and aim to maintain the float voltage on the battery. At no time does the wattage or amperage have the dramatic fluctuation down to 0 like I mentioned above.

I’ve checked all the connections with a multimeter. Tightened down all the connections to the battery, MPPT, etc. My wiring from the solar panel to the MPPT is 10 gauge (only 16 feet in length total). The wiring from the MPPT to the battery is 8 gauge.

As per Renogy’s solar panel troubleshooting steps, I performed an open circuit voltage test, with it passing – needs to be within 10% of Voc; I measured 20.4V at the panel connections vs. the panel’s Open-Circuit Voltage (Voc): 21.2V. I then performed a short circuit current test, with it passing too – needs to read 50% of the spec sheet number or greater; I measured 4.6 amps with the panel’s Short-Circuit Current (Isc) being 6.10 amps. Therefore the panel is okay. I also cleaned the panel with water and paper towel to ensure it was clean.

I’ve also “disabled the charger” for several minutes, then turned it back on, letting it go through the charge cycle. After a few minutes in float charge, it goes back to the fluctuations.

I have no idea what’s causing this. Can someone please provide some guidance as I’ve done all the appropriate troubleshooting that I’m aware of?

I’ve attached screenshots from the MPPT charging parameters and history, as well as the SmartShunt.


MPPT battery settings 1.png

MPPT battery settings 2.png

MPPT history with fluctuations.png

SmartShunt battery settings.png

SmartShunt SOC.png

MPPT Controllersbattery charging
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3 Answers
ludo avatar image
ludo answered ·

This is probably the autotracking of the mppt calculating the right settings every 10 minutes.

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cdn4runnersolar avatar image cdn4runnersolar commented ·

Thank-you for your response ludo.

If we look at the screenshot I provided titled “MPPT History with Fluctuations”, we see that it’s a reflection of a 5 minute snapshot (from 13:00 – 13:05) of the Solar Power (Wattage) and Battery Current (Amperage) during Float Charge. From 13:00 to just past 13:03, you see the dramatic fluctuations in both wattage and amperage, going down to 1 watt and 0 amps, which is occurring every few seconds. It almost looks like a sine wave. If this was the MPPT algorithm trying to maximize the charge efficiency, wouldn’t this fluctuation be shown in 10 minute increments (like you suggest), not every few seconds?

In comparison, I’ve attached a screenshot of a 30 minute snapshot of Solar Power (Wattage) and Battery Current (Amperage) from today, from 11:53 – 12:23 during Float Charge. We see that both the wattage and amperage remains very stable, hovering around 13-15 watts and 0.8 – 1 amps. Around the 12:12 time stamp, there is some fluctuation, but it’s only 1-2 watts and 0.1 – 0.2 amps, which I would expect.

Yesterday’s results almost seem like the MPPT just couldn’t figure out what wattage and amperage to use to keep the battery in Float, or there was something going on with the battery. I’m still puzzled on this, as if it was a battery issue, then it should be repeating the same issue today? I would think at least.

MPPT history with fluctuations 2 - Sept 24 2022.png

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ludo avatar image
ludo answered ·

Could you pls write a graph with current vs battery voltage maybe 1 hour ?

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cdn4runnersolar avatar image
cdn4runnersolar answered ·

Sorry for the delay. We had 2 straight days of rain and my battery didn't get into a Float charge as a result.

I've attached 2 different graphs, both 1 hour in duration (11:40 a.m. - 12:40 p.m.) from today while the battery was in Float Charge. One graph shows battery voltage and battery current, the other is battery voltage and solar current. I have not witnessed the same wattage and amperage fluctuation since Friday, so these graphs do not reflect my issue. I'm keeping an eye out to see if it repeats itself. If it does, I will provide graphs with the same information.

I'm also going to monitor the readings on the SmartShunt, to see if it reflects the same fluctuation as witnessed on the MPPT.

Sept 28 2022 - battery voltage & battery current.png

Sept 28 2022 - battery voltage & solar current.png

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