Can I just charge batteries one at a time (with the BMS only connected to one)

[JustPractical]

Finally wiring in my Growatt12k to my four paralleled EG4 LIFEPO4's. I have no load on anything yet. To bring the batteries up to charge, my plan was to conenct the BMS cable from the Growatt to ONE of the batteries, set the battery to master, and then charge it with the Growatt. Then power everything down, set the next battery in the rack to master, connect the BMS cable, and charge it. I was going to work my way through all 4, bringing each up to charge. THEN, I was going to shut all down, connect up all BMS cables, give each battery a unique ID, and power everything up (all four batteries and then inverter). I'm doing this so that all batteries start out at similar charge (they are paralleled). I believe this is best. Opinions? Not necessary? Reminder - right now there is no load. Sidenote - I do not own a charger, so do not currently have another method to charge the batteries.

 

[sunshine_eggo]

This sounds like a big hassle. Why not charge them all at once? In parallel, they will level themselves out.

Additionally, with their pre-charge circuits, there shouldn't be a huge surge between them as you're making connections. I'd wire them up in parallel (power and data) and charge.

Concerning your reminder: I'll remind you that your Growatt has a substantial load on the order of 180W in idle power consumption, so you will ALWAYS have a load if the inverter is on even if nothing is drawing power. Additionally, that 180W load 24/7 is going to consume 4320/5120 = 84% of the capacity of one of your batteries or 21% of your total battery capacity. If you use it in standby mode for charging only, then yes, there will not be a consequential load.

 

[JustPractical]

This sounds like a big hassle. Why not charge them all at once? In parallel, they will level themselves out.

Additionally, with their pre-charge circuits, there shouldn't be a huge surge between them as you're making connections. I'd wire them up in parallel (power and data) and charge.

Concerning your reminder: I'll remind you that your Growatt has a substantial load on the order of 180W in idle power consumption, so you will ALWAYS have a load if the inverter is on even if nothing is drawing power. Additionally, that 180W load 24/7 is going to consume 4320/5120 = 84% of the capacity of one of your batteries or 21% of your total battery capacity. If you use it in standby mode for charging only, then yes, there will not be a consequential load.

True (I try not to think about it - seems like a big waste). I want to try the standby mode - says it needs a 500W load to wake up, and I'm not sure my sump pump will pull that. I have to test. As for charging, I thought I had to top/bottom balance them.

 

[JustPractical]

It would be a good amount easier to just connect all teh communicaiton cables and then go for it. BUT...I thought they needed to be balanced to start?

 

[sunshine_eggo]

It would be a good amount easier to just connect all teh communicaiton cables and then go for it. BUT...I thought they needed to be balanced to start?

When in series, critical. When in parallel, it matters a wee bit above "barely at all."

 

[Substrate]

Heh, although with dodgy products, it can reduce variables and expose the poor performers up front, rather than later when the system acts strangely. And then one does them individually anyway to find the culprit.

 

[JustPractical]

When in series, critical. When in parallel, it matters a wee bit above "barely at all."

Cool. I have limited time at the site, and would like to be able to "charge them all at once" - I know it doesn;t change the overall time, but I can walk away and not chewck on them for a while and know they are ALL charging up.

 

[sunshine_eggo]

Cool. I have limited time at the site, and would like to be able to "charge them all at once" - I know it doesn;t change the overall time, but I can walk away and not chewck on them for a while and know they are ALL charging up.

This is often the motivating factor for me for exactly the same reason. WHen I'm at my off-grid site, my time is limited. Sometimes doing something 95% right and having extra time for other tasks is better than 99.9% right and having to stare at something or check it regularly.

 

[JustPractical]

It *looks* like everything charged fine. I had a "BMS Communications error" about 15 minutes in on the charging, and the unit stopped charging. Shut off everythign and put everything back on, and it was all good after that. Eggo, thanks for the advice. Made the process MUCH smoother. Got the batteries charged from 49% to 99% in about 8 hours (from utility)