EG4 LL Battery Discharging and Charging Slower Than The Rest

[robby]

I am pretty sure this is an Internal resistance issue but I find it really odd.
I have three Fortress eFlex 48V Batteries in Parallel with one EG4 LL Battery. I was doing some checks today and when the batteries are charging the eFlex's are all pulling in like 21 Amps but the EG4 is Pulling 12 Amps. After they all get up to 100% SOC the voltage reading on all four batteries is the same (Looking at them via PC software) all the cells are well matched and everything is fine but the EG4 took 30+ minutes longer to reach 100% SOC.

On discharging test I made the eFlexs produced 7.2 amps each while the EG4 only contributed 3.5amps to the common load.
I pulled out my Amp meter and confirmed what the software and display on the EG4 and eFlex was saying is correct.

I am by no means a battery expert so I am wondering if this could cause problems for my eFlex batteries over the long term and exactly why there is such a big mismatch in current draw when the voltages are the same.

 

[robby]

OK @Dzl , @FilterGuy , @Hedges any help please. All the wires are the same length 4 AWG to the Busbar where they then connect to 2/0 AWG to the 250A Breaker and then Inverter.

 

[MisterSandals]

while the EG4 only contributed 3.5amps to the common load.

Double check or clean and treat the EG4's battery and bus bar connections? Any warmth in wiring or connections?

Happen to have a pic that shows battery wiring?

 

[robby]

Double check or clean and treat the EG4's battery and bus bar connections? Any warmth in wiring or connections?

Happen to have a pic that shows battery wiring?

Thanks for the reply
No heat that I felt but I have a thermal cam and will take a look at it tonight when they switch on to discharge.
I will double check the terminals in the morning.

 

[MisterSandals]

My gut feel is that it might be a matter of different internal resistances of the 2 pack types.

Would like to see wiring though. A lot of eyes sometimes find something...

 

[FilterGuy]

My first guess is that the primary difference is that the internal resistance of the EG4 is larger. Both brands of batteries will have very low resistance, but if one has .02mohm and the other has .04mohm it could create the symptoms you are seeing. (Even if the cells are identical, the difference could be in the BMS)

As @MisterSandals has stated, check to be sure the connections are all good to the EG4, but it seems unlikely you would see a 2x difference in current due to the connections unless it was *really* bad.

One thing you could try is to swap the EG4 connections with the connections on one of the fortress batteries. If the problem stays with the battery, it is some difference in the battery. If the problem stays with the connection, it is a problem with the connection.

I am wondering if this could cause problems for my eFlex batteries over the long term

Yes, the reflex batteries are being worked harder.... so they will wear out sooner. However, as @Will Prowse has pointed out a few times, calendar aging may be a bigger factor than cycle aging.


BTW: This touches on something I have wondered about for a while. I am always careful with battery arrangement, but if the BMS's have a large variance in resistance, it could swamp any effects of the arrangement.

 

[Will Prowse]

Can you post a picture of your connection points and bus bars.

 

[robby]

Thanks for the help guys.
I think @MisterSandals and @FilterGuy hit the nail on the head.
I did checks again with different loads and the current is always almost half that of the eFlex Batteries. I suspect it's because the Fortress eFlex batteries use an EV battery relay on the BMS to engage the power while the EG4 uses Mosfets. It is either that or the EG4 batteries internal resistance really sucks!

I did a thermal image and let me apologize in advance for not centering the temp on the hottest spot but there was only a 2deg C difference at the hottest point which is the LED at the Top Right which measured 27c. The two second warmest parts are the Terminals on the 250A breaker which was about 26C. You can see 5 wires on the bottom one and that is coming from the 4 batteries plus one small wire that goes to my Precharge resistor near the LED. The Top Terminal is where the 2/0 cable goes to the Inverter. On the left is the 4 Terminal 600A Victron Busbar.

BTW EG4 Battery terminals are totally cool at 24c. I will not bother posting a picture because there is no temp variations between the cool front panel and terminals.

Same measurement with the house being powered at around 3.5Kw.
20Amps from each eFlex Battery and 11 Amps from the EG4.
I now have mixed feelings about buying this battery.

 

[FilterGuy]

I suspect it's because the Fortress eFlex batteries use an EV battery relay on the BMS to engage the power while the EG4 uses Mosfets.

Yup!! That would explain everything.

 

[robby]

Yup!! That would explain everything.

I had matched the length of all the 4 AWG cable runs at 7ft per leg and this battery could be shortened by 3ft, per leg but the math is telling me I am still two levels of magnitude short in making a dent. This might require some modifications to the BMS in the EG4 to make it work with a duplicate relay. Just thinking out loud but suggestions are really welcome.

 

[FilterGuy]

Just thinking out loud but suggestions are really welcome.

Unless you need that extra current from 1 of the 4 batteries under max load, I would say live with it...... or replace the EG4

 

[robby]

Unless you need that extra current from 1 of the 4 batteries under max load, I would say live with it...... or replace the EG4

Thanks, I think I am just going to live with it. In all these years doing electronics and knowing about ESR and measuring it, this is the first time the reality of it has been so noticeable to me.
One lesson I take away from this is that if you have a limited sun hours to charge your batteries during the day it really pays to get a really good batteries. Today it is overcast and my eFlex's hit 100% SOC by 2pm. The EG4 was at 78% when last I checked at 3pm.

 

[johnnyding]

I observed same slow charging/discharging on EG4 battery. I have a 5 KWh A123 24V battery bank (bought from Big Battery, equipped with OevrKill's BMS) connected in parallel with a 5 KWh 24V EG4 battery on the same bus bar and use same size/length cable. The charging/discharging rate of EG4 is 1/6 of the A123 power bank. I really doubt that EG4 has higher internal resistance.

 

[robby]

I observed same slow charging/discharging on EG4 battery. I have a 5 KWh A123 24V battery bank (bought from Big Battery, equipped with OevrKill's BMS) connected in parallel with a 5 KWh 24V EG4 battery on the same bus bar and use same size/length cable. The charging/discharging rate of EG4 is 1/6 of the A123 power bank. I really doubt that EG4 has higher internal resistance.

Now you have me worried. The only reference I have is my eFlex batteries and those use a Relay not Mosfets. I know the eFlex's have a super low internal resistance so I figured that it was the EG4 using Mosfets that was the problem.

So what do you think is the issue? Six time slower is madness!

I also now have three cells that go up to very high voltages during the charge cycle and then equalize after a couple of hours.
I am now getting the feeling that these are definitely B quality cells inside.

 

[johnnyding]

To be honest, I didn't expect this issue, that is why I went to this forum with query "Eg4 battery parallel" and found this thread when I discovered this issue first time. I won't throw any bad words on EG4 battery or SignatureSolar. Actually I did lots of research before pulling the trigger on EG4 battery. I tend to think it is caused by prod spec difference due to cells made by different battery manufactures.

Is there a standard/doc to see the normal range of the internal resistance of good cells?

 

[johnnyding]

One update, after discharging for a while, the voltage of the individual cells was dropped to ~3.33v, the discharging current per each battery bank were almost equal. Later when the voltage of the individual cells was dropped to 3.28v, the discharging current of EG4 battery was 5 times of A123 battery bank. My interpretation is the internal resistance of the LifePo4 battery changes under different SOC, and the change varies among cells made by different manufacturers.

 

[robby]

One update, after discharging for a while, the voltage of the individual cells was dropped to ~3.33v, the discharging current per each battery bank were almost equal. Later when the voltage of the individual cells was dropped to 3.28v, the discharging current of EG4 battery was 5 times of A123 battery bank. My interpretation is the internal resistance of the LifePo4 battery changes under different SOC, and the change varies among cells made by different manufacturers.

My Charge and Discharge rate lag by almost half that of my eFlex batteries no matter what.
I have three EG4 cells that will get up to 3.8xx volts during the last 10% of the charge and that worries me.
They do get balanced down to normal after an hour or so but I know something is wrong because it's always the same three cells. All my eFlex cells charge up within proper parameters and only take a few minutes to balance out correctly.

 

[koppted]

My Charge and Discharge rate lag by almost half that of my eFlex batteries no matter what.
I have three EG4 cells that will get up to 3.8xx volts during the last 10% of the charge and that worries me.
They do get balanced down to normal after an hour or so but I know something is wrong because it's always the same three cells. All my eFlex cells charge up within proper parameters and only take a few minutes to balance out correctly.

Have you tried switch over the connections as mention earlier in this thread? Transpose the connections either on the busbars or for which ever one is closest battery to the inverter, and see if you get the same results.

 

[robby]

Have you tried switch over the connections as mention earlier in this thread? Transpose the connections either on the busbars or for which ever one is closest battery to the inverter, and see if you get the same results.

Nope! I know that is not the problem. All of the cable are the same length and the ends are all perfect and have been examined with a thermal camera. Even if I cut that one batteries cable length in half it would make less than a 1% improvement on the resistance seen.

I also talked to an Installer today who said he had put in about four of the EG4 batteries as additional batteries at various locations. I asked him did he see a Charge/Discharge difference and he said yes, it was about 3 times lower!
Then he said to me out of the blue that he thinks something is wrong with the cells as he is seeing all sorts of high values when they are charging. I told him I saw the same thing and he said oh well they are B Quality cells and for the price he really expected nothing else.
I mentioned the new SOK 48V packs and he said what does it cost, I told him the price and he said "More B Grade Cells". You cannot build a bank for that price with Grade A Cells.

 

[koppted]

Interesting. I wonder what the extent of the "B quality" designation can be visually verified. It's got me wondering if perhaps the distributor sends racks with "A quality cells" to reviewers like Will Prowse, David Poz, and other youtubers, and then send the "B quality" Ones to the Average Joe. Anyone want to risk their warranty and open up one of these?