100/50 MPPT keep going into Float before batteries charged

[Gongbong]

Hi,

Last few days I have noticed the MPPT was dropping it’s charge to around 40W during the middle of the day, normally this is around 700w from the two Longi panels and is maxing out the 50A MPPT limit.

I thought it was something wrong with the solar panels but checked and there was plenty of sun available at round 981 w/m2.

I then noticed the MPPT was going into float mode before the batteries are charged, tried two different battery banks and when both got to around 70% charge if would go to float, nothing has changed from my side on the MPPT before it started doing this, I did an update for the MPPT a few days ago but it mentioned it was only for Bluetooth.

I physically disconnected it as I thought it was a time out thing and it charged in bulk for a about five seconds then goes straight into float, obviously it’s hitting a voltage limit somewhere.

MPPT is set to rotary switch position 7 - Smart Lithium (LifePo4).

So the only thing I can see is to go to “User Defined” or “Expert mode”, but not sure what to set the various settings at for either setting.

Any help to get the right settings ?, what would be the suggested settings.

Below are screenshots of the settings available, thanks for any assistance.

At over 980 w/m2 I was only getting 48W

Below is User Defined settings

and Expert settings.

[lxonline (LX)]

What is more important is the trends.

Is your battery reaching the 14.2v?

Can they? What is their information?

@Gongbong

Any help to get the right settings ?, what would be the suggested settings.

Answering this requires we know what bettery is being used.

[Gongbong]

Hi,

Below are the trends.
Battery bank is 2 x 200A Li-Time in parallel LiFePo4
Also tried a single 200A Smart Renogy LiFePo4

[Ludo]

I set the absorption time to 8 hours

[Gongbong]

And voltages? Are you running lifepo4?

[Ludo]

Voltages look ok, yes , i have lifepo for house and starter battery in my rv

[pwfarnell]

One cause of this is if you have developed a high resistance between your MPPT and the batteries so the MPPT sees a higher voltage. A loose connection or an isolator that is not making good contact.

Another is if there is an unbalanced cell in the battery and the battery is disconnecting, check your battery via Bluetooth.

You showed voltage traces, what about current during these same periods.

[lxonline (LX)]

Shouldn’t be necessary for lithium.

[Ludo]

Well, at least the voltage will be stable and the batteries will be at 100% when the sun goes down.

It works for me…

[lxonline (LX)]

Its an interesting idea.

[xavierlh1 (Xavier Le Héricy)]

I notice your screenshot of a smartphone app that shows the amount of light directly in W/m2. Do you mind sharing what app that is, because all I find on GooglePlay are light measurement in Lux and FC. Having the value directly in W/m2 instead of doing the conversion would be a plus.

[Gongbong]

Funny you should say that about an unbalanced cell, the problem showed itself when I had the Renogy battery plugged in.

The Li-Time’s were at 100% so I swapped in the Renogy to get it charged up, I left it for a few hours and noticed it wasn’t accepting much charge, this is when I started to fault find what was happening,

I was checking connections, cables, solar panel efficiency, MPPT temperature etc this is when I noticed the MPPT was in float mode, I was doing this over a three day period on and off due to other commitments.

Thinking about it the problem was only when the Renogy was plugged in, as the Li-Time bank
was reaching 100% when I returned to check on them.

I have had problems with this Renogy battery from the start, it worked fine for about 1 month, then would drop anywhere from 10% to 30% of it’s indicated SOC randomly for no reason, it would disconnect the inverter even though it was showing 15% SOC, then all of a sudden it would go to 0% and the battery would switch off, upon waking it up I checked the cell voltage and cell 2 was showing lower voltage that the other cells, typically 2.7v while the others were at 2.8v.

I contacted Renogy about this and got the run around, had to repeatedly provide the same information about 5 times to them, in the end they said it was normal what was happening and the BMS will cut off when the cells drop below 2.7V, I explained when it happened the other cells were all at 2.8V or even 2.9V and only cell two was at 2.7V and I suggested there was a faulty cell in the battery, I continued to get the run around from them so I put the battery aside and purchased a 100A Li-Time to test it, and the Renogy sort of got forgotten about.

After using the Li-Time for a few months and finding it worked perfectly I purchased 2 x 200A Li-Times, returned what I could of the Renogy gear and purchased Victron.

So saying all that, I think you’re right there is a cell problem in the Renogy battery causing the issue, I had sort of forgotten about the problem with this battery as it doesn’t get used much now, I will contact Renogy again and see if I can get it replaced / repaired or refunded, I am very happy with the Li-Times.

Thanks for your help.

[Gongbong]

Its a dedicated Solar Irradiance Meter from amazon, I looked at Lux meters but was recommended to get a meter that gives w/m2 as it’s easier with no conversions needed.

This one is good, it connects via BT works in real time, it’s a tiny device, was 1/2 to 1/3 the price of all the other ones.

I went for this one as the others didn’t have bluetooth, so you can set it on the roof, walk away then keep monitoring it via BT

When I was fault finding this issue, I was able to determine instantly that the panels were receiving sufficient power and should have been working.

I have another meter coming from Ali to test / measure the performance of individual panels, it looks like a good device hopefully it works as advertised.

[xavierlh1 (Xavier Le Héricy)]

Much helpful. Seeing a smartphone app screen, I jumped to the conclusion that it was just an app, but I’m good with a dedicated device.