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greg-griffin asked

4 of 100/50 MPPT seem to have problems at max load

I have 4 of 100/50 MPPT charging at 12V and my max possible input from the panels is 600W. The MPPT should be capable of 700W at 12V.

When all are running at the same time, if the output from each MPPT goes over 500W (for all of them), periodically 2 to 3 of the MPPT will shut off. There appears to be a momentary voltage output spike, but no errors, nothing to tell me why. They will all start right back up again. It could another few minutes and then repeats.

They all have the same settings. I'm running fans on them to keep them cool. I'm guessing or assuming that when they are all outputting at full strength, some are seeing that as batteries having reaching their voltage capacity or something like that?


I'm running 400AMP busbars and 2/0 cables going very short distances (a couple feet). I have 8 LiFePo batteries that each have a desired charge rate of 50amps and a desired charge of 14.6v...which each MPPT is set to.

Ideas on what is causing this and how to avoid or test?

MPPT SmartSolarovervoltageshutdown
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Alexandra avatar image
Alexandra answered ·

@Greg Griffin

Slow down the charge rate. Your (most likely) batteries are shutting down and causing the spikes as there is an overshoot in production with nothing to absorb it. Is it happening more at a higher voltage on the batteries?

How are the batteries wired? Maybe it is just one or two doing it because of current sharing.

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greg-griffin avatar image
greg-griffin answered ·

Batteries are all parallel and each individually has a desired charge rate of 50amps (x8 batteries)...making the desired rate that can EASILY be received of 400amps....Each of the MPPT are set to 50amp out. Are you saying that if the output was 40amp each that would perhaps help? That reduces my ability to charge as the rest of the potential is lost?


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Alexandra avatar image Alexandra ♦ commented ·

Some batteries at a higher SOC need the charge current to lower as balancing is happening and cells can overshoot so the bms shuts down.

So each one is wired to the next down a line? Not each up to the bus bar? Current sharing will most likely be the issue with the end batteries taking a beating.

See the book Wiring Unlimited

https://www.victronenergy.com/upload/documents/Wiring-Unlimited-EN.pdf

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JohnC avatar image
JohnC answered ·

Hi @Greg Griffin

This may be the mppts tracking. While V is lower than the target setpoint, each will track every 10 minutes over a wide V range several times. Takes maybe 10 seconds, but power loss is minimal. This may be what you're seeing, and it's normal.

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greg-griffin answered ·

Interesting. So the tracking only happens at maximum solar input? Only happens when loads are great and the light flicker. I saw a voltage spike to 16v and believe something similar happened a month ago when at peak input on a very sunny day, the voltage spiked to 32v and blew all of my circuits throughout the entire motorhome. $2,000 later (and a lot of work) I would like to know for sure and not repeat. If I turn off just one of my MPPT during peak time, then everything is fine.


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Alexandra avatar image Alexandra ♦ commented ·

@Greg Griffin

In your original post when you say there are spikes are you referring to the pv voltage or the battery voltage side? John C is referring to voltage on the solar panels side. Tracking there up and down is normal.

If it is on the battery side and therefore the 12v circuit side, that should not be happening. Very abnormal.

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JohnC avatar image JohnC ♦ Alexandra ♦ commented ·
The tracking is noticeable on the battery side too, but it's invariably downwards with both V and A. Not to say that the other mppts wont try to compensate (if they can), but batts are a great buffer. So I wouldn't expect much of upward spike. Unless of course a BMS is tripping the batt connection.
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greg-griffin avatar image greg-griffin Alexandra ♦ commented ·
I know the PV goes up and down and can monitor that with the Cerbo GX. The spikes were on the battery side. LED lights flicker and sometimes turn off and then back on. One large spike blew out circuits everywhere.
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Alexandra avatar image Alexandra ♦ greg-griffin commented ·

@Greg Griffin

So then we are back to the bms shutting down and refusing charge. The overshoot of 200A of charging would be an issue definitely then if the batteries were not absorbing it. @sPro had a good suggestion as well with lowering charge voltages, if it is not a current sharing issue causing one or two to shut off.

BTW you cannot have a Bluetooth smart network and a GX in the same setup it is listed as a limitation in the manual.

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greg-griffin avatar image greg-griffin Alexandra ♦ commented ·
Just to clarify. The max output of my 4 MPPT is about 50amps...total of 200AMP. The average capability of charge for the batteries is 400amp with the ability to take on as much as 1,400amps in total as the max charge rate combined. So, perhaps the BMS is shutting down, but even with battery charge at 80%, this is happening, and I can't imagine the BMS is overwhelmed with such low amperage. It is confusing. Lowering all voltage and amperage to see if that helps.
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Alexandra avatar image Alexandra ♦ greg-griffin commented ·

@Greg Griffin

My bad. Edited the post. Was meant to say 200A.

Is the bms 50A continuous or 50A peak?

Its not that the bms cannot take the charge, sometimes the balancing internally cannot keep up and one or two cells go over volt and the bms has to reject charge.

It depends on the BMS. Some of the ratings are a bit funny that way.

Did you charge up each one individually before connecting them? Also how is the current sharing set up? Wiring has alot to play here as well. With some set ups the end batteries are the issue ohms law being what it is.

So are the batteries each wired to the bus bar with the mppts interspersed between them?

Or are they connected to each other with the end batteries up to the bus bar with the mppts connected to that?

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spro avatar image
spro answered ·

14.6v is the absolute limit for a 4 cell LiFePo4 and the BMS will disconnect the battery if it gets any higher. This wil cause the voltage of the systeem to spike.


Try setting the the absorption voltage a bit lower, something like 14.4 of 14.2 volt. The batteries are still going to charge to 100% SOC, only the last 1-2% may take a few minutes longer.


Also are the MPPT's Bluetooth enabled (Smart)? If so ad them to one VE.Smart Network. This way they all sync the charging state

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greg-griffin avatar image greg-griffin commented ·
I will try a lower voltage setting. 14.6 is the recommended charge voltage from BigBattery with an optimal charge rate of 50amp for each battery (180Ah OWL LiFePo x 8). The MPPT are all connected to a Cerbo GX, which I thought would automatically sync them, but when looking at the charts, they don't always do the same thing at the same time. Yes, all are connected individually to the same network directly with a cable and show connected to the same network when using BT to directly connect to each. Is there something more or a setting where I have to more clearly specify this sync? I thought it would be the default and automatic.
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greg-griffin answered ·

So, with a little more trial and error, I needed to reduce all of the MPPT down to only 400Watts of output each or max charge rate of 29amp. I move the cable legs connecting the bus bar from the MPPT output and the bus bar for the batteries. Legs now are connected into the middle of 250amp bus bars so power is more easily distributed on the bar. All 2/0 copper cables connecting. 500amp smart shunt.

I'm a little disappointed that I cannot fully output from all MPPT. I've had about 550W output on sunny days from each (which led to the problem), but if the output goes much over 400W for each (1600w total) for any period of time 2 or 3 of the MPPT shutdown and restart. There appears to be a momentary voltage spike. Batteries have plenty of capacity, not fully charged, and the charge rate is 1/5 of their desired charge rate. It also appears that my first MPPT typically does not shut down...usually the other 3 take turns.

Wish I had something more to chase after as to why there is a little spike and reset of MPPTs. Will try testing the voltage coming out at MPPT and input at batteries to see if there is a difference. Nothing feels hot. Any ideas?



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