Growatt SPF-12000T DVM-MPV Off Grid Inverter A/C charger onboard does NOT have absorb function

[adnubian]

Guys, in talking with Growatt support over the last couple of days it seems that the 12KW off grid unit does not have a proper A/C charger for lithium banks. I have been testing it with a 30kw lithium bank (LG Chem cells) 560ah and I can have the unit charge the packs up to 57.8v or any other setpoint but once it reaches it, it never goes into absorb mode from what I can tell. It cuts all current and runs a maintenance charge of 50w. The 57.6v drops immediately to lets say 55v or so and while the inverter is still handling the loads, the battery voltage never increases past that point. I let it set in that state for an hour to watch and actually saw the voltage decrease .1v, Obviously with such a large bank 50w most likely will not do much for charging. I asked this question of Growatt and they confirmed that the charger is a 2 stage A/C charger that does not have an absorb stage. How can they put out a unit that cannot do this? Am I missing something here? I look forward to some input before I return this thing and swear off Growatt for any solar needs.

Thanks all and I look forward to your responses.

 

[snoobler]

Guys, in talking with Growatt support over the last couple of days it seems that the 12KW off grid unit does not have a proper A/C charger for lithium banks. I have been testing it with a 30kw lithium bank (LG Chem cells) 560ah and I can have the unit charge the packs up to 57.8v or any other setpoint but once it reaches it, it never goes into absorb mode from what I can tell. It cuts all current and runs a maintenance charge of 50w. The 57.6v drops immediately to lets say 55v or so and while the inverter is still handling the loads, the battery voltage never increases past that point. I let it set in that state for an hour to watch and actually saw the voltage decrease .1v, Obviously with such a large bank 50w most likely will not do much for charging. I asked this question of Growatt and they confirmed that the charger is a 2 stage A/C charger that does not have an absorb stage. How can they put out a unit that cannot do this? Am I missing something here? I look forward to some input before I return this thing and swear off Growatt for any solar needs.

This is known behavior with Growatt AC chargers. Well documented on http://www.watts247.com.

It's NOT that way with solar. It follows bulk/absorption and float with PV input, so when you say "solar needs," you mean "AC charging needs" as the solar charging occurs in the expected way.

 

[Ampster]

Lithium does not need an absorb (constant voltage) stage to be healthy like lead acid does. The only thing you might be missing woiuld be time for balancing to take place. The voltage decrease you are seeing is the natural settling of the cells and has nothing to do with the behavior of the charging stage.

 

[adnubian]

This is known behavior with Growatt AC chargers. Well documented on http://www.watts247.com.

It's NOT that way with solar. It follows bulk/absorption and float with PV input, so when you say "solar needs," you mean "AC charging needs" as the solar charging occurs in the expected way.

That is good to know. That being said, the MPPT knows what to do so I will see how that goes. Charging via solar today and looking forward to seeing what happens at 58.4v.

 

[snoobler]

The AC charger behaves more like an emergency generator... On at a low voltage and off at a high voltage.

 

[Ampster]

On at a low voltage and off at a high voltage.

Essentially a Constant Current single stage source? Is the current configurable?

 

[snoobler]

Essentially a Constant Current single stage source? Is the current configurable?

Yep. As I recall from my last foray into the manual, the charging currents on those units can be controlled and split amongst solar and AC.

It was a feature that I was frustrated Victron didn't offer... until I installed my GX.

 

[adnubian]

The AC charger behaves more like an emergency generator... On at a low voltage and off at a high voltage.

Makes sense. I had periods of time today when the unit went into float mode and let the voltage rest all the way back to 56v. Annoying when a 2.7kw load is drawing down on the battery. My Outback 8048a was much smarter - it matched the load and only allowed that much PV power so that it is a net zero type situation. Growatt could use that sort of logic

 

[adnubian]

Yep. As I recall from my last foray into the manual, the charging currents on those units can be controlled and split amongst solar and AC.

It was a feature that I was frustrated Victron didn't offer... until I installed my GX.

Overall, yes you can specify Max AC amperage i.e. 30a and total amperage systemwide up to 180a.

 

[adnubian]

Lithium does not need an absorb (constant voltage) stage to be healthy like lead acid does. The only thing you might be missing woiuld be time for balancing to take place. The voltage decrease you are seeing is the natural settling of the cells and has nothing to do with the behavior of the charging stage.

My loads average 2.6kw so it is always discharging lol. I hope Growatt fixes some of the charging logic as well as handling loads while floating by matching the load draw and allowing solar energy to match it.

 

[snoobler]

My loads average 2.6kw so it is always discharging lol. I hope Growatt fixes some of the charging logic as well as handling loads while floating by matching the load draw and allowing solar energy to match it.

Doubt they will. They've done it this way for years across models.

How narrow can the range be? You might be able to get similar functionality by having the charger cut in and out in a narrow voltage range.

 

[adnubian]

Doubt they will. They've done it this way for years across models.

How narrow can the range be? You might be able to get similar functionality by having the charger cut in and out in a narrow voltage range.

I definitely do not believe that granular of a level is available on this unit. It is quite generic in features and taking with support is an painful process. Should have gone with a MPP. I wish they made a 12kw.

 

[snoobler]

turn on at 44-51.2V
turn off at 48-58V

Better if you had lead acid.

51.2V is a decent loaded "float" voltage for FLA/AGM, but not so hot for LFP.

I'd try 51.2-54.4 and play with #11 to try and throttle the use of grid a bit.

Far from set and forget though.

 

[adnubian]

View attachment 46125

turn on at 44-51.2V
turn off at 48-58V

Better if you had lead acid.

51.2V is a decent loaded "float" voltage for FLA/AGM, but not so hot for LFP.

I'd try 51.2-54.4 and play with #11 to try and throttle the use of grid a bit.

Far from set and forget though.

I see where you are going with this, I will give it a shot. Thanks

 

[snoobler]

I see where you are going with this, I will give it a shot. Thanks

When shit doesn't work right....

WORKAROUND!!!!

 

[Ironman]

Am I wrong or isn't the "absorption charge" just designed to put in enough to replace the self discharge losses occurring in LA?

 

[snoobler]

Am I wrong or isn't the "absorption charge" just designed to put in enough to replace the self discharge losses occurring in LA?

No. That's what float does.

Absorption is the phase needed to fully charge the battery at the absorption voltage. Barely needed on a LFP battery. Desperately needed on a FLA/AGM/GEL.

 

[Ampster]

Am I wrong or isn't the "absorption charge" just designed to put in enough to replace the self discharge losses occurring in LA?

Absorb stage is just a constant voltage for a specified time or until current drops to a specific voltage. It is a necessary stage for Pb (LA) batteries but not for Lithium. Unlike Pb batteries Lithium does not need to be fully charged after discharge. As far as self discharge of Pb batteries, the Float stage or trickle charge is what does that. Float is also not needed for Lithium because the self discharge is so low.
EDIT: @snoobler beat me to the answer.