Pre-commission battery balancing

[stephen.m]

Hi,

I’m finalizing preparation for the GB/FB/outdoor batteries.

The EG4 battery manual calls for ensuring all batteries are the same voltage prior to connecting them all together.

In my case, all 12 of those batteries will be connected to a bus bar.

Batteries will be here in a couple weeks, I am not sure what voltage they will arrive at. 50%? I have one chargeverter, I plan on charging each battery to full prior to connecting them all together.

Is that the way to go? Or should I aim for all of then being within an arbitrary target? The closer the better but what’s good range to aim for?

Lastly, once they’re all within this range, and I connect them all together by turning on the disconnects on the bus bar, how long should I wait for the individual battery voltages to even out before turning on the inverters?


Alternatively to the chargeverter, would it be better (or worse) to use one of the FB’s to charge the batteries? I have a string of 8 panels that I could use for that. Note that initially I won’t have any string PV, they will come in a couple months ago. So when the GB/FB gets commissioned I will only have 45 panels with microinverter on GB’s smartport.

 

[wpns]

As long as they are within a volt of each other, go ahead and parallel them, then charge them all in parallel with the CV till they are all full and balanced.

Which battery? I know the WallMount have precharge circuits, but you have to power them up in the right sequence:
BMS off
Battery breaker(s) on
Inverter DC breaker on
BMS on.

 

[stephen.m]

Thank you. They’re 280 AH outdoor wallmount.
That sequence would also apply to getting charged with the CV?

 

[BaylentheSky]

As long as they are within a volt of each other, go ahead and parallel them, then charge them all in parallel with the CV till they are all full and balanced.

Which battery? I know the WallMount have precharge circuits, but you have to power them up in the right sequence:
BMS off
Battery breaker(s) on
Inverter DC breaker on
BMS on.

Yep! Most people are worried about the higher voltage battery dumping massive current into the lower ones. The truth of the matter is, and I have experienced this myself, a voltage delta of less than a couple volts don't matter at all. In fact, the current transfer happens soooo slow, it literally takes a long time (I want to say 10 hours but I left them overnight so no clue really how long) for the batteries to reach equal voltage if you connect them in parallel like that. You don't even see a spark when trying to connect. That's one of the signs of very low current flow.

 

[wpns]

Thank you. They’re 280 AH outdoor wallmount.
That sequence would also apply to getting charged with the CV?

Yup. Hadn’t thought of reverse-pre-charging the CV output caps, that’s a great idea!

 

[DC_Ripple]

I typically charge each battery until it is full.
When the battery will not take any more current from the charger.
I know people recommend the same voltage (or pretty close), and that is ok.
Fully charged [100% SOC] puts all the batteries at the exact same starting point.

Either way works, I just like to see the batteries fully charged before connecting them together.
This lets me know brand new batteries are working correctly.

 

[wpns]

I typically charge each battery until it is full.
When the battery will not take any more current from the charger.
I know people recommend the same voltage (or pretty close), and that is ok.
Fully charged [100% SOC] puts all the batteries at the exact same starting point.

Either way works, I just like to see the batteries fully charged before connecting them together.
This lets me know brand new batteries are working correctly.

Indeed, this is another way of making sure the batteries are at the same voltage, and depending on the BMS, will work just fine.

Be aware that charging the batteries till BMS cutoff isn't the same as fully charging them and letting them finish balancing (see the WattCycle parallel threads) but that's a whole rathole. The OP has EG4 PPODWM batteries, so he ought to be able to set the CV to an appropriate voltage and monitor the cells till they are fully charged and balanced. IIRC they need to be over 3.5V and less than 40mv delta...

You can also monitor them with the BMS tools and the appropriate interface. I make time-lapse movies like:

http://dotnetdotcom.net/20251016_Batt2.mp4

(Cyan outline is balancing) but that's the kind of geek I am.