How are LifePo4 CC & CV charging phases affected by inverter draw?

[blasetheodore]

I tried searching the forum before posting, apologies if I missed it.

I'm trying to understand how 'Constant Current' & 'Constant Voltage' charging phases (from solar chargers) are affected by realtime draw on the system (i.e. inverters, fridges, etc).
And if the draw-during-charge affects the batteries negatively, is there a way to isolate the charging from the drain to prevent it?

I'm also confused by what equipment actually determines those CC/CV phases. I always thought they were controlled by the charge controller. But I've also read that the battery BMS affects the CV phase by limiting its draw. If this is true, is a phase mismatch something that would cause problems?

Lastly (and possibly most relevant) does 'constant current' imply a fixed current? Or does it just imply a 'maximum' current?
In other words, what happens when a cloud comes by and the solar charger stops charging?

In case it matters, I have 3x 100ah LifePo4 batteries (=300Ah @12v). Which I believe gives me 300A combined max input current.
And that is fed by a 60A MPPT controller (max 1200W, min 0W).
And the battery is connected to a 3000W Inverter.

 

[Hedges]

CV/CC means deliver a particular current so long as voltage is below limit. Once voltage limit is reached, keep voltage constant and current tapers off according to load (e.g. battery charging.0

Discrete SCC and inverter, the SCC might be set for a particular current but inverter steals some or all for loads, even drains battery.
Integrated like hybrid/AIO, it could keep track of battery current and crank up PV harvesting to deliver target charge current plus loads.
Some discrete equipment, e.g. Victron charge controller with Cerbo or Midnight Classic with Whiz Bang Jr., battery current is measured and SCC told to deliver more.
AC coupled GT PV inverter with battery inverter (like mine), battery current is also measured and regulated.

FLA, typically 0.13C constant is desired. For my AGM, 0.2C is what I've set. Lithium, often up to 0.5C is fine so for most people, all available PV can be used. Except if cold; near freezing max "C" rate for lithium is reduced.

Sometimes, voltage or current changes due to load or clouds, and system may switch to different charging phase when this is not desired.

Your system has SCC capable of 0.2C, so let it do all it can, unless quite cold. But if inverter is an inverter/charger with AC input, that could deliver more.

 

[McKravitts]

I tried searching the forum before posting, apologies if I missed it.

I'm trying to understand how 'Constant Current' & 'Constant Voltage' charging phases (from solar chargers) are affected by realtime draw on the system (i.e. inverters, fridges, etc).
And if the draw-during-charge affects the batteries negatively, is there a way to isolate the charging from the drain to prevent it?

If the inverter is drawing more current than the charge controller(s) supplies, the batteries will provide the excess with no harm to them unless the total barttery draw exceeds the batteries capacity, in which case the BMS should terminate or limit charge current.

If the inverter is drawing less than the current that the charge controller(s) supply the batteries will charge at a slower rate with no damage to them.

I'm also confused by what equipment actually determines those CC/CV phases. I always thought they were controlled by the charge controller. But I've also read that the battery BMS affects the CV phase by limiting its draw. If this is true, is a phase mismatch something that would cause problems?

That's an excellent question. Improper matching of all charging devices can lead to false alarms by one or more of the charging devices.
Example: A inverter/charger sounds an alarm if it detects too high a voltage during CV phase, if a solar charger is set to a higher cv voltage.

Lastly (and possibly most relevant) does 'constant current' imply a fixed current? Or does it just imply a 'maximum' current?
In other words, what happens when a cloud comes by and the solar charger stops charging?

Constant implies just what it says; constant current. It is fixed by the settings of the charging device. The total charging current must not exceed the batteries capacity. This usually isn't a problem but if it is you can use a multiMPPT. The multiMPPT can be set to charge from the grid when the solar charging current is too low.

In case it matters, I have 3x 100ah LifePo4 batteries (=300Ah @12v). Which I believe gives me 300A combined max input current.
And that is fed by a 60A MPPT controller (max 1200W, min 0W).
And the battery is connected to a 3000W Inverter.

Constant implies just what it says; constant current. It is fixed by the settings of the charging device. If multiple charging devices are used, the total could exceed the batteries max charge capacity.

The max charging current is not always equal to the AH specs of the battery. In fact most battery manufacturers specify a lower max than the AH capacity. 30 to 50 % is common. In general the lower the charge current the longer life span.

 

[Ampster]

@Hedges answered you questions. I just want to clarify that the charge controller determines the transition from Constant Current to Constant Voltage based on the battery voltage. Also in the case of a solar charge controllers the current is not alway constant when shade reduces current but the transition occurs the same way based on battery voltage.
EDIT: and @McKravitts also added additional detail while I was drafting the above