Growatt 3000 solar charging weirdness??

[apctjb]

I have two Growatt 3000's (48V), configured to operate in single phase parallel. (6000W combined output). Both are connected to 560AH LiFePO4 battery (2P16S)

Each Growatt has its own MPPT charge controller connected to identical 2.5KW PV arrays (5000W total, 2500W per inverter)

When I first connect the array to inverters/charger controllers, each starts charging and the charging current is identical for each. But after a short time charging currents begin to vary until one inverter is charging at full capacity and the other is at 0 amps. (see photo below inverter 1-30A solar charging, inverter 2-0A).

Identical arrays, identical inverters (operating in parallel, identical settings, same battery...so what would explain the variance in charging currents? Anyone else noticed this occurring with their all in one inverters?

 

[snoobler]

That is normal behavior once you hit absorption voltage when using multiple charging sources.

The second phase of charging is constant voltage - the battery will not accept more voltage than is needed to maintain the absorption voltage. Once absorption voltage is hit, the chargers taper current to hold voltage. Once one can supply all the current needed to maintain the absorption voltage, the second reduces current to zero and drops to float.

 

[apctjb]

Interesting that one drops to zero, while the other maintains, rather than both reducing equally.

If the inverters were not operating in parallel (ie AC outputs not tied and communications cable removed) then would both taper equally?

I assume I can test this by observing at a time when the battery voltage is below (and has not exceeded) the absorption setpoint. then both would operate at near equal charging output? Correct?

Thanks

 

[apctjb]

Related question. Any way to know when the Growatt's or MPP have hit the absorption setpoint and switched to CV charging? Is there a indicator ?

 

[apctjb]

Double checked the manual and it appears there is a display that indicates when in CC vs CV vs Float. I have not noticed this in operation, but will check. Hopeful the voltage /cell adjust with battery type...

 

[snoobler]

It's not interesting at all. It's expected. The chargers are completely ignorant of one another. The charger that happens to be able to output slightly higher current will always win resulting in the other charger going to zero. Victron SCC can be placed in a VE.Smart network where they coordinate with each other, but without that communication between them, they will behave exactly as you describe.

Those /cell are specifically for 48V lead-acid systems. The AC charger on those is weird and suboptimal. It doesn't follow a 3 phase. It charges to and holds 52V. It is not effective for fully charging any battery chemistry.

 

[apctjb]

Thanks !The Growatt manual claims 3 step charging (bulk, absorption, float) and the voltage setpoints for absorption and float are adjustable for different battery chemistries. (I have mine set to 56V and it is reaching that voltage)

I appreciate the feedback but now am confused. Are you saying that the Growatt MPPT charger doesn't work as claimed and is crap (weird/suboptimal) and are never going to charge my 560AH LiFePO4 batteries correctly? If that is the case I feel pretty stupid for buying them after reading every post on this forum I could find that mentioned them and did not run across this before. Hoping you can clarify your comments further.

 

[snoobler]

The solar charging and AC charging are different. When charging from solar, it's 3 phase. When charging from AC, it's 2 phase.

From:

Growatt 24V 3kW Stackable 120V 2kW MPPT 80A – Off-Grid Inverter SPF 3000TL LVM-24P – Watts247 Wholesale

watts247.com

Utility/Generator Charger tips:
The generator charger is a different beast to the solar charger. (Does not utilize the Bulk and Float Charge settings)
It works on a float valve type principle. (triggers when battery voltage drops below that on setting 12 – set the voltage higher than current battery voltage to start charging right away)
Stops charging from Generator when setting 13′ s voltage is reached
Will not start charging the battery again until it drops below battery voltage – in setting 12.
Setting 01 set to SBU to activate setting 12 and 13.
Setting 02, is the Max charging current from Solar + Utility/Generator
Setting 11, is the Maximum Generator/Utility charging current @ your battery voltage (not at 120V)
Setting 14, make sure this setting includes the option to charge from utility/generator (see manual)
Note, setting Setting 11 too high for your generator may cause your generator to falter at startup, and cause the Inverter Charger to lose synchronization with the Generator (58 to 63Hz), if in doubt start small, and work your way up.

 

[John Frum]

Once absorption voltage is hit, the chargers taper current to hold voltage.

The charger doesn't taper current.
The battery draws from the charger that has the slightly higher voltage.

 

[snoobler]

The charger doesn't taper current.
The battery draws from the charger that has the slightly higher voltage.

Please advise as to where I set the voltage on my battery. I've looked all over it, and I can't find an interface.

 

[John Frum]

Please advise as to where I set the voltage on my battery. I've looked all over it, and I can't find an interface.

The battery draws based on voltage differential.

 

[Huck]

Everyone is aware of the firmware update?

 

[apctjb]

Thanks; I appreciate the comments and education. A lot to learn...

Correct me if I am mistaken but my understanding is that during the bulk charging phase the MPPT charger does not restrict current flow, whatever the array can put out, goes to the battery. Once absorption setpoint is reached the MPPT charger switches to constant voltage (output voltage = absorption setpoint voltage) and the current tapers as the voltage differential between battery voltage and CV voltage diminishes until battery voltage hits float voltage. Float charging is really a misnomer because its not really charging, its more is like a float valve in a water tank, the level (voltage) is maintained during float charging.

Do I have this right?

So here's a question. Once it reaches float, what has to happen for charging to resume? Does the battery voltage have to drop to another voltage setpoint and if so what do you call that setpoint or is it a passage of time thing and then the charging cycle starts again?

 

[apctjb]

Everyone is aware of the firmware update?

My units are running on firmware version 502.06 20200707-B; is there a newer firmware than that? If so can you provide a source for downloading.

Thanks

 

[Darren Orange]

Thanks; I appreciate the comments and education. A lot to learn...

Correct me if I am mistaken but my understanding is that during the bulk charging phase the MPPT charger does not restrict current flow, whatever the array can put out, goes to the battery. Once absorption setpoint is reached the MPPT charger switches to constant voltage (output voltage = absorption setpoint voltage) and the current tapers as the voltage differential between battery voltage and CV voltage diminishes until battery voltage hits float voltage. Float charging is really a misnomer because its not really charging, its more is like a float valve in a water tank, the level (voltage) is maintained during float charging.

Do I have this right?

So here's a question. Once it reaches float, what has to happen for charging to resume? Does the battery voltage have to drop to another voltage setpoint and if so what do you call that setpoint or is it a passage of time thing and then the charging cycle starts again?

Just so you know this is the same issue I am finding with the LV5048. It seems like it is leaving about 10% give or take and not putting it into the battery, not that it can't but it seems that it is a firmware charge curve gooeyness that needs to be corrected. I'm trying to figure out what the solution might be. For anything Lithium Bulk and Float should be the max voltage you want to charge to, mine is 57V. You can test this easily by adding large load you'll likely see the some weirdness with a jump in solar draw and then when you cut the load the solar draw will drop. A microwave is a easy load to test this with. Of course use this around peak time of day otherwise it is hard to see.

 

[Huck]

My units are running on firmware version 502.06 20200707-B; is there a newer firmware than that? If so can you provide a source for downloading.

Thanks

As far as I know that is the latest.

 

[Huck]

Just so you know this is the same issue I am finding with the LV5048. It seems like it is leaving about 10% give or take and not putting it into the battery, not that it can't but it seems that it is a firmware charge curve gooeyness that needs to be corrected. I'm trying to figure out what the solution might be. For anything Lithium Bulk and Float should be the max voltage you want to charge to, mine is 57V. You can test this easily by adding large load you'll likely see the some weirdness with a jump in solar draw and then when you cut the load the solar draw will drop. A microwave is a easy load to test this with. Of course use this around peak time of day otherwise it is hard to see.

That makes sense to me as well. I believe there is some sort of charge sensing with a added time duration involved. I have set mine to 58v with a float of 52.2v and it will never get any higher than say 55.6. It just hovers at 55- 57v for hours. This is all on grid power btw. I can't seem to make sense of it either. I'm almost ready to purchase something else. I'm just hoping we get a new Firmware update soon that fixes all this. The setting of the settings should be left to the customer and not the machine.

 

[apctjb]

You can test this easily by adding large load you'll likely see the some weirdness with a jump in solar draw and then when you cut the load the solar draw will drop.

Could it be that you have "solar power balance" enabled? From the description it sounds that solar input would vary with loads. In theory this sounds like a nice feature as loads will be powered first by solar if excess is available, rather than drawing out of the battery and having to replenish. That said I don't know if it works this way in practice...

 

[apctjb]

Had a chance to test the Growatt Solar Balance feature this afternoon. Battery had already reached float, with no significant current flowing to battery. I turned on a larger load (1.4 kw heat gun). As expected there was an initial ~25A discharge current flowing from the battery (I have a shunt at battery) but then this discharge current quickly decrease down to zero even though the load continued to run. So where was the 1.4 kW to power the heat gun coming from? Solar! Despite being in float mode (no solar charging current) the inverter with MPPT charger was drawing power directly from the array without dipping into the battery. When I turned the load off there was a short period of charging current and then current quickly decreased to zero to maintain float. Throughout the process the solar charger remained in float mode.

Pretty cool to be able to power loads directly without dipping into the battery. Depending the application seems like this could increase daily total energy harvest in cases where battery is typically in float later in the day.

 

[Darren Orange]

Had a chance to test the Growatt Solar Balance feature this afternoon. Battery had already reached float, with no significant current flowing to battery. I turned on a larger load (1.4 kw heat gun). As expected there was an initial ~25A discharge current flowing from the battery (I have a shunt at battery) but then this discharge current quickly decrease down to zero even though the load continued to run. So where was the 1.4 kW to power the heat gun coming from? Solar! Despite being in float mode (no solar charging current) the inverter with MPPT charger was drawing power directly from the array without dipping into the battery. When I turned the load off there was a short period of charging current and then current quickly decreased to zero to maintain float. Throughout the process the solar charger remained in float mode.

Pretty cool to be able to power loads directly without dipping into the battery. Depending the application seems like this could increase daily total energy harvest in cases where battery is typically in float later in the day.

Any idea how to turn this kind of feature off. I am personally losing huge amounts of power though out the day due to this. Likely close to 25%. How can I kill this float mode thing. My batteries are no where near full and its doing this behavior also this is with the LV5048 so it has the same issue.