MPP Solar 3024 AIO not going into bulk charge

[Sparktastic]

Hi guys,

I suspect this might be a bug in the MPP firmware??

I have a PIP GEW 3024 AIO.

The system is completely off grid and has the following attributes:

Battery - 8 cell x 300ah Lifpo4
BMS - Daly 8 cell
Solar - 5 x 415w panels in series.
Inverter battery profile - 'User' (as all of the LI profiles seem to throw a BMS comms error, if selected).

Bulk charge voltage 28.8v
Float charge voltage 27v

The problem I'm having is that even after discharging down to 50% SOC overnight, the inverter will only charge up to the float voltage the next day. Clearly, this is not taking the cells up to 100% SOC as the charge current drops to back to almost nothing, once the battery reaches 27V

Can anyone shed any light on why these inverters do not activate Bulk charge, before switching to float?

To get around the issue (somewhat), I've increased the float voltage to 27.8 (3.475v per cell) which seems to bring the batteries up to close to 100%

 

[RCinFLA]

Check you do not have too much voltage drop on interconnect/cabling between inverter and batteries with charging bulk current.

 

[shvm]

Inverter battery profile - 'User' (as all of the LI profiles seem to throw a BMS comms error, if selected).

It is bound to throw the comms error unless you figure out BMS comms.

Clearly, this is not taking the cells up to 100% SOC as the charge current drops to back to almost nothing, once the battery reaches 27V

The cells are technically full. It is the BMS that is failing to recognize that charging is complete and failing to display 100% SOC.

Can anyone shed any light on why these inverters do not activate Bulk charge, before switching to float?

I think it is already doing it. You need to observe the voltages carefully while charging is taking place.
The charge controller should apply a bulk voltage of 28.8v and then after some criteria is met (absorption time usually), it should switch to Float applying 27V.
This is inline with the expected behaviour of Bulk and Float stages.

If your LFP battery shows 27V across it with 0 current , it is fully charged. That is what it is.

 

[Sparktastic]

For anyone following this thread..
I've been in contact with MPP.

MPP comments -

"Bulk charge is not activated unless the pack voltage drops to 25v"

So basically, unless you discharge your pack to 3.125v per cell (or about 15% SOC) overnight, you will never activate Bulk charge. This Bulk charge 'trigger' voltage is not adjustable, unlike other chargers.

MPP's solution to this, is to suggest setting the Float voltage to 8*3.6v or 28.8v

I'm not comfortable leaving the pack Floating at 28.8v for potentially 6hrs a day, so I'm going to experiment with the 'Equalise' function instead.

I'm setting the Float voltage to 27.2v and activating daily Equalisation voltage of between 28.0 - 28.8v for 30mins or so.

This will give the active balancer a chance to top balance to around 3.5-3.6v per cell before switching back to Float.

I'll report back after a few days with results