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Battery Unequal Disharge Rates

JCSchwarb

JCSchwarb

Solar Enthusiast
Joined
Nov 26, 2022
Messages
499
Hi DIYSolar Family,

Appreciate help on what is causing two of ten 48V EG4 LifePower4 batteries have lower states of charge, see image attached. I am using the master cable and mode USE for all EG4 inverters. All batteries have their Ethernet comms cable and dip switches are all different.

I have noticed this twice now over several weeks. One morning I noticed the two were off, no LEDs were light while the other eight were. I would think these battery BMS would toggle the charging and discharging to keep these batteries more balanced.

Appreciate help with cause and a fix for this.

-Jay
 

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Pretty sure this isn't going to help you but might help others. DIY your batteries, and use the KISS principal. I have heard too many stories of these batteries, not good ones either. The more complicate things get the more problems.
 
Jay, how is the wiring configured, all equal length? Bus bar orientation? Why the need for com cable if you're using USE?

@nc73 agreed, money saved towards more panels, better inverter, more tools, less headaches.
Thanks to all the help and resources here my 22kwh of DIY has been working great.
Sharing for others in the future. Wiring isn't the prettiest for the BMS's, it's on my list to clean up when I add a 3rd pack. Easy to move, whole thing sits on some nice wide solid steel casters.
 

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JCSchwarb said:
Hi DIYSolar Family,

Appreciate help on what is causing two of ten 48V EG4 LifePower4 batteries have lower states of charge, see image attached. I am using the master cable and mode USE for all EG4 inverters. All batteries have their Ethernet comms cable and dip switches are all different.

I have noticed this twice now over several weeks. One morning I noticed the two were off, no LEDs were light while the other eight were. I would think these battery BMS would toggle the charging and discharging to keep these batteries more balanced.

Appreciate help with cause and a fix for this.

-Jay
Click to expand...
I have the same problem with two of my six batteries. I have them in the 6 battery rack as it comes from Signature Solar Both bars facing up. Battery 1 and battery 3 from the top down are always one light lower on the SOC meter then the other 4 after a few days of discharging. Once the sun comes out they all balance right away.

Next time I have my system down for repairs I’m going to flip the negative bare to see if it helps. If that don’t help I’m going to mark those packs and move them to another random location in the pack of six To see what happens.

dave
 
Jack Rabbit Off Grid said:
I have the same problem with two of my six batteries. I have them in the 6 battery rack as it comes from Signature Solar Both bars facing up. Battery 1 and battery 3 from the top down are always one light lower on the SOC meter then the other 4 after a few days of discharging. Once the sun comes out they all balance right away.

Next time I have my system down for repairs I’m going to flip the negative bare to see if it helps. If that don’t help I’m going to mark those packs and move them to another random location in the pack of six To see what happens.

dave
Click to expand...
My cables are all methodically made and cut to the same size. The batteries are not giving me anywhere near the rated 50 kWh. Mine are no. 1, rack one and no. 2 from top on rack 2.
 
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42OhmsPA said:
Jay, how is the wiring configured, all equal length? Bus bar orientation? Why the need for com cable if you're using USE?

@nc73 agreed, money saved towards more panels, better inverter, more tools, less headaches.
Thanks to all the help and resources here my 22kwh of DIY has been working great.
Sharing for others in the future. Wiring isn't the prettiest for the BMS's, it's on my list to clean up when I add a 3rd pack. Easy to move, whole thing sits on some nice wide solid steel casters.
Click to expand...
All wires are the same length. I bought these rack batteries for a neat, low complexity installation so I wouldn’t have to deal with anomalies like I am having.
 
Are they getting the chance to be fully charged at least once a week and sat there for a while? I noticed my felicity solar batteries will start to deviate if they have been sitting at a lower rate of charge and not able to be fully charged for a week but one good charging session gets them all right back together again.
Both of my homemade batteries with JBD BMS also do this so honestly I wouldn't worry about it too much. The trick is to get them fully stuffed at least once a week from my experience.
 
JCSchwarb said:
My cables are all methodically made and cut to the same size. The batteries are not giving me anywhere near the rated 50 kWh. Mine are no. 2 one rack and no. 4 on the other rack.
Click to expand...
How many rack batteries do you have?

Is it possible to remove the 2, open them and manually top balance?
 
If welded, I might consider temporarily removing the com cables and set the chargers to USER and set absorb/CV to 3.48v dc per cell and float to 3.41v per cell during a few sunny days. Lower the loads and let the bms go into balance mode, which might be around 3.4 v dc per cell.
 
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Perhaps you need a much higher resolution system monitor so that you can actually know what is going on at a level deeper than LED indicators different three different times you pass by the rack.

FWIW.. I currently have two battery packs a 150 amp hour and a 160 amp hour the smaller capacity pack always charges ahead of the bigger pack and discharges ahead of the larger pack. There is a place when changing from charging to discharging where if we are discharging the small pack is lower than the higher pack and then we begin to charge it takes time for that smaller pack to overcome and get ahead of the larger pack but they only ever see the same state of charge near the bottom and near the top. Typical maximum disparity in the state of charge is about 7%. Totally normal behavior.
 

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I was thinking my problem was my lower bulk/absorption charge voltage of 56.8v But now I’m rethinking that. When I purchased my batteries the recommendation for charge was 57-58v bulk and 56.5 absorption/float. I thought that was a bit much so I just went with my what my Victron recommended default setting of 56.8v bulk/absorption and 54v float.

I now see Eg4 or Signature Solar has changed that high bulk-absorption-float voltage recommendation. I see now they recommend lower than even Victron default setting @ 56.2v Bulk/absorption and 54v float.
 
MrM1 said:
How many rack batteries do you have?

Is it possible to remove the 2, open them and manually top balance?
Click to expand...
I have quantity of 10 - 5.1 kWh 48V. I am not interested into doing depot level maintenance on 2 month old batteries. I will build my own and send this crap back if this is needed to fix these things. The other part that ticks me off is the inverters are set to go to grid at 47V and this am my batteries are at 44.5V.
 
TomC4306 said:
Why would you think that?
Is it stated in a manual or spec sheet somewhere?
Click to expand...
The manual doesn’t go into this level of detail. Studying standard BMS theory, each cells voltage is monitored to enable or disable charging for each cell. This enables the pack to stay equalized and to protect from over or under voltage. My assumption is that each battery that plugs into each other via Ethernet would balance each complete battery to one another.

The inverter does have a n equalizer function, but have not investigated if it would be useful.
 
TomC4306 said:
?

Anywhere you feel comfortable and your battery runs comfortably. No cutoffs no big cell deviation.

Bulk/absorb - 55.2 - 56.8 (3.45 - 3.55)
Float - 53.6 - 54.2 (3.35 - 3.3875)
Click to expand...

Option 12 (back to util) 47V

Opt 13 (back to Batt) 48V

26 (bulk V) 56

27 (float V) 54.5

29 (low voltage cut off) 45V
 
MrM1 said:
I can't recall on the EG4 batteries. Some sellers of rack mount batteries have bolted busbars, some have welded. If welded would be more difficult.
Click to expand...
The EG4 racks are bolted. I have my pos and negative at opposite ends
 
JCSchwarb said:
The EG4 racks are bolted. I have my pos and negative at opposite ends
Click to expand...
He’s talking about every single individual cell inside the effected battery case. Eg4’s are welded together 16s. Not worth it, that’s what the 5 year warranty is for though if you can get them to honor it. I’ve read horror stories.
 
You say this shows up after a few days of discharging. Have you read the threads where the inability of the BMS to accurately assess the SOC is discussed? Any current under 2 amps is ignored. I suspect that your batteries are all fine, and really at a similar SOC.
Have you checked the voltage at each battery? If they truly were at such a different SOC the voltage would have to be different, which just can't happen when you have them properly on a bus.
When you think they are low, charge them and see how much they take.
I've only got 5 EG4 Lifepower4, and that's enough to lower average current below the point the BMS counts it.
I noticed the same difference in the indicator lights, but I can tell you that in my case, it is certainly a false indication that shows up after a few days of not being fully charged.
In summary, I don't think you have a real problem.
 
Before you do something drastic like start taking things apart, what is the difference in cell voltage? Watch that as you charge and see how each battery responds. You do use the BMS_test software to read the bms info, correct?
I notice that you have ten of these. That means that every minute you are charging or discharging at less than 1000 watts the bms is not accurately tracking SOC.
 
JCSchwarb said:
The manual doesn’t go into this level of detail. Studying standard BMS theory, each cells voltage is monitored to enable or disable charging for each cell. This enables the pack to stay equalized and to protect from over or under voltage. My assumption is that each battery that plugs into each other via Ethernet would balance each complete battery to one another.

The inverter does have a n equalizer function, but have not investigated if it would be useful.
Click to expand...
This absolutely doesn't happen. However, when they are on and connected to the bus bar you can be assured that the pack voltage is very close.
 
Screenshot (18).png

In case you're not familiar with it, this is a screenshot of the software you can use to monitor your batteries. This is the first thing you should do, if you haven't.
 
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