MPPT Power Limited

Question

question

muhammed asked Aug 17, '21

MPPT Power Limited

Hi

Client has 3 x 8kVA Quattro Units setup in 3 phase. 2 x 250/100 MPPTs. 62.5kwh Lithium Ion Battery.

I have installed 2 x MPPTs (250/100) with 5.4kW on each. Initially the above two would not produce more than 2.8kWp together - I had initially thought this to be due to the panels facing East/West.

The panels connected to the new MPPTs are facing North but somehow all the MPPTS are being limited to a total of 2.8 kW - I confirm this by shutting off one or more MPPTs. When I do this, the output of the others goes up, but all still below 2.8 kW. Any idea where the setting is that is limiting the system?

Kind Regards

MPPT Controllers

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Alexandra ♦ commented · Aug 17, 2021 at 06:58 PM

@Muhammed

Does it happen if they are disconnected from the gx device?

Are the batteries smart and connected to the gx?

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Modifications Space

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Answer 1 · 2021-08-17T19:33:53Z

muhammed answered · Aug 17, 2021 at 07:33 PM

@Alexandra

I have not tried disconnecting the communication cable from the MPPTs to the GX Device.
Yes, the batteries are smart and connected to the BMS Can on the Gx Device.

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Alexandra ♦ commented · Aug 17, 2021 at 07:57 PM

@Muhammed

If you do unplug (reset them to stand alone) as a test you as will get an error #67 bms lost.

Are the mppts set to use their max charge power?

The other thing is some managed batteries will limit the solar on the system when new especially if it is trying to balance itself. Can take up to a week to settle down. I have seen this on pylons, blue nova to mention a few.

Once you have worked out whether it is the mppts, or the bms, or neither, there are some settings in maybe the dvcc and ess menus.

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Answer 2 · 2021-08-17T23:54:12Z

Elimac answered · Aug 17, 2021 at 11:54 PM

Does this happen with battery full or when charging? Check the DVCC settings to see if the charge current limit is active and what value is set. But in your case, it is likely not the issue. The BMS might be doing this for some reason. Check what you can about the battery cells, any reason why BMS might be limiting charge current.

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Answer 3 · 2022-04-24T11:09:57Z

CristiMV answered · Apr 24, 2022 at 11:09 AM

I‘m starting to get the same issue. My system has a Quattro, a Fronius Primo connected to AcOut, a Mppt 150/85, Color Gx and Pylontech batteries. Once the batteries are fully charged, the MPPT output goes down. This started to happen since couple of days, no changes were performed in the meantime. I’ve checked the dvcc settings, the grid export settings, I even downgraded the Color Gx FW…still the same. Any clues?

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kevgermany ♦♦ commented · Apr 24, 2022 at 08:32 PM

Sounds like it's working properly. If the batteries are fully charged, then the output from the MPPT has to go down to the level of any loads, otherwise the batteries will be damaged by overcharging.

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CristiMV kevgermany ♦♦ commented · Apr 24, 2022 at 09:46 PM

You are correct up to a point, but in my case I’m exporting to the grid the surplus, both AC and DC. I don’t have any limit set on ESS, the only limit is set on Fronius to reduce its power based on the grid voltage. And it wasn’t the case, the voltage didn’t reached the level where the Fronius should start reducing. So with all these, the MPPT is throttling down. And again, it worked fine until couple of days ago, and I didn;t changed anything in the meantime. The only change I see is that the CCGX applied the last FW 2.85 some days ago. I loaded back the 2.84 and I disabled the auto update. Still no change.

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Answer 4 · 2022-05-08T07:09:07Z

ikeakayke answered · May 08, 2022 at 07:09 AM

Same happening here, it worked good for a few days(recently installed system), meaning during charging of battery any excess DC from MPPT was also used to power the loads/feed-in but not any more. If I set ESS to keep batteries charged then the MPPTs ramp up to full power simultaneously charging the batteries and powering the loads.

I am on latests firmwares with everything (quattro 10kva, cerbogx, mttp 250/100) and using lead acid gel victron batteries so no bms involved

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majstermod commented · Sep 15, 2022 at 12:46 PM

Have you tested other ESS modes?

Seems ESS mode is somehow related to this power limitation, however in my case "keep batteries charged" makes things even worse.

In my setup everything works perfect since early morning when battery isn't full.

Then since the moment battery fully charged ESS modes don't work as they should when 2 MPPTs are connected (with one MPPT before it worked ok).

ESS modes tested with full battery
1. Keep batteries charged

MPPT1 is disabled, MPPT2 has reduced power below power demand from system.

Power is taken from grid.
Disaster.

2. Optimized with battery life.

MPPT1 is disabled, MPPT2 has reduced power below power demand from system.

Power is taken from battery.

Far from optimal, I lose PV production but at least I don't pay for energy from grid.

3. Optimized without battery life

Most logical. Both MPPTs deliver power sufficient to cover loads plus a little bit more to keep battery floating.

Rapid load changes are covered by battery till MPPTs adjust and then battery is Floating again.

Correct.

4. Workaround

In order to ballance cells in battery I use ESS mode "Optimized without battery life" and "Minimum SOC" =100%. It works as I would expect from mode keep batteries charged. Loads are covered by PV production and battery usage is kept on very minimum level.
Acceptable and useful to run once per couple of weeks.

@nickdb what do you think?

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Answer 5 · 2022-09-13T10:47:52Z

majstermod answered · Sep 13, 2022 at 10:47 AM

I have similar issues since I connected second MPPT.
I have 16 panels facing South.

8 connected to one MPPT 150/45 and remaining 8 to another MPPT 150/45.
For one month I had only one MPPT and it was adjusting power to the load almost without visible delay.
Since I connected second MPPT load balancing works strange.
Example: full sun exposure at noon and and 1500W of load. One MPPT1 generates around 1500W, second MPPT2 0W. Once load drop or battery full MPPT1 reduces power accordingly.
When load increased again MPPT1 increases power almost instantaneously and MPPT2 generates 0W for one minute or so then kicks in and fill the gap.

Another time both MPPTs generates the same power.

Next time MPPT2 generates all required power and MPPT1 nothing.

In general two MPPTs setup adjust power with significant delay in comparison to setup with one MPPT and from time to time lagging MPPT doesn't kick in even if load is significantly greater than one MPPT can handle.
Mostly it happens just before battery reach 100% SOC.

It took 2 minutes to enable MPPT1 and mostly due to the fact BMS allowed charging, what increased load by more than one MPPT can generate.

Once battery full (BMS disabled charging) power was reduced correctly.

After some time equal power share.

It looks like system is able to react quickly to reduced load, but have issues when load increases by small amount or remains stable.

Settings

DVCC enabled

Maximum charge current 50A

Feed-in disabled

HW

Multiplus II 48/5000/50-70 GX

MPPT1 connected to VE.direct

MPPT2 connected through VE.direct-USB

Lifepo4 battery 100Ah ... therefore I use 50A charge limit

When it works correct it looks like follows:

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nickdb ♦♦ commented · Sep 13, 2022 at 10:54 AM

There is no load-balancing in the sense of an even, or semi-even distribution of load.

You might see one unit doing the heavy lifting if that is all that is required. At full power all units will be adding what they can, but beneath this it won't be evenly spread.

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nickdb ♦♦ commented · Sep 13, 2022 at 11:07 AM

What batteries are these? When the battery hits the CVL the mppt's will throttle, on the one pic you can see the voltage is higher than others.

Given the level of charge, it is probably a result of the BMS and cell balancing, or possibly there is voltage drop due to cabling - the latter you can check with a meter under load at the terminals of all the devices/battery.

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majstermod nickdb ♦♦ commented · Sep 15, 2022 at 11:25 AM

There is some serious bug in multi MPPTs setup.

It never happened before in y setup with one MPPT.

Scenario

Before test I changed battery mode in ESS to "Keep batteries charged".

Battery full and low AC load 300-440W.

1. MPPT1 is sleeping, MPPT2 is serving half of required power despite good sun exposure and the rest is taken from battery.

2. Hairdryer started to increase AC load. MPPT2 is increasing power and MPPT1 is waking up.3. After couple of seconds both MPPTs are delivering required power and even more.4. As long as hairdryer is running, both MPPTs deliver power and also charge battery.

5. Hairdryer turned off. Both MPPTs slowly reduce power.
6. Further reduction of power, producing just a little bit more than AC load.

7. Finally again MPPT1 disabled and MPPT2 doesn't cover power demand.

So essentially when battery is full and AC load low then system isn't able to control MPPTs to provide required power and is discharging battery instead. I loose energy and battery is frequently cycling despite ESS setting to keep it charged.

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nickdb ♦♦ majstermod commented · Sep 15, 2022 at 12:16 PM

Have you followed my advice and when there is load to measure, with a meter, at the terminals of each device: inverter, mppt's and battery? - to see if there is any variance in voltage.

You have also not stated what the battery/BMS is.

Multiple MPPT's work fine, it is widely deployed, at home I have 3 powering my own system no problems.

This just looks like the voltage has crept up so the mppt(s) go to sleep and the battery discharges until it reaches the setpoint to wake the chargers.

Have you also checked both MPPT's have been set the same?

You could also try enable DC feed-in but set the limit to 0.

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majstermod nickdb ♦♦ commented · Sep 15, 2022 at 01:33 PM

I added battery details yesterday ... my mistake it landed in wrong place.
Answer converted to comment so it is now below this comment.
I have thick cables crimped in hydraulic press and there is no difference in voltages, which could lead to misleading info for MPPT.

Please take a note all of this happens with low loads like 400W, so voltage drops aren't noticeable.
I will try to record video with some heavy load, however ESS mode without battery life works correct, MPPTs are always delivering as much power as required.

Voltages checked with voltmeter under 500, 1000, 1500W, 2000W loads.
My meter can measure up to one decimal place.
Voltages on all terminals are exactly the same at each load (MP, Battery, Lynx, MPPT1, MPPT2) . They are also consistent with these shown by MPPTs in Victron Connect App.

MPPT settings. Both are externally controlled by MP, but anyway switch on both devices is in position 7 (Lifepo4). Float voltage as in battery specification.

DC feed-in with limit 0.
I can try some day, now ESS mode without battery life works ok.
All of all if main goal of battery life is to balance it by assuring it will be fully charged once per 2 weeks or so, I can define scheduled charging and achieve exactly the same.

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majstermod commented · Sep 14, 2022 at 07:16 AM

My point is on first picture there is around 1600W of load.

PV capable to deliver 2x1300.

MPPT2 producing 1300 and 300 taken from the battery, while this gap could be handled by MPPT1.

I have more PV power available than required to handle my loads and battery is drained anyway.

High voltage on MPPT1 looks like open circuit so this MPPT isn't working at all at this moment.

My expectation is to use PV power first if it is available.

My battery:

https://sakopower.com/product-sako-48v-100ah-lithium-battery

Cables
Multi - Lynx Distributor 70mm2 less than 1m

Battery - Lynx 70mm2 less than 1m

MPPT1 - Lynx 16mm2 less than 50cm

MPPT2 - Lynx 16mm2 less than 50cm
All 3 voltage measurements (from MP sensor connected to battery and from both MPPTs) are same to the second decimal place, so I don't see voltage drops due to cabling.

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majstermod commented · Sep 14, 2022 at 07:24 AM

When AC load is low then it is harder to wake up lagging MPPT.

Yesterday MPPT2 was serving loads and MPPT1 was off for almost one hour, while it could feed the battery.

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