2 LiTime 100ah Bluetooth LiFePO4 in parallel

[crashmaster]

I have 2 LiTime 100ah bluetooth LiFePO4 batteries wired in parallel and it appears by looking at the BMS of both batteries that only one battery is under load. I attached photos of both BMS.

If anyone has these batteries wired in parallel do you have the same issue when looking at both BMS?

Thanks!

 

[Jon R]

Disconnect the one that appears to be discharging. Does the other one then begin delivering current to your loads?

 

[Jon R]

Also, does “StandbyFull” in your BMS app display for the second battery mean the battery is in some sort of standby mode where it is disconnected internally? Maybe look for a software switch to change the mode to normal operation.

 

[Jon R]

Sorry - I now see Vic has already asked you these questions in the other thread.

 

[Vic Harder]

Great minds think alike or ...

 

[crashmaster]

Good questions Jon. I took the one battery that was operational down to 20% SOC. The other battery never did Discharge anything. I removed the parallel wiring then discharged and charged the batteries individually again. Wired them back together. Same result.

I have another email into LiTime but it takes them at least 24 hrs to respond. The last responses seem like they came from a chatbot as they didn’t really address the issue. I also called the phone number in China but just got a recording and was not able to speak with anyone.

Will see what happens with emails from Li Time tomorrow.

 

[Jon R]

Good questions Jon. I took the one battery that was operational down to 20% SOC. The other battery never did Discharge anything. I removed the parallel wiring then discharged and charged the batteries individually again. Wired them back together. Same result.

I have another email into LiTime but it takes them at least 24 hrs to respond. The last responses seem like they came from a chatbot as they didn’t really address the issue. I also called the phone number in China but just got a recording and was not able to speak with anyone.

Will see what happens with emails from Li Time tomorrow.

It’s probably good the second battery never connected once your first battery was at a significantly lower state of charge. The battery to battery current would have been very high and possibly overheated the interconnect wires.

That makes me wonder, did you connect the two batteries when one was near fully or fully charged and the other was at a significantly lower charge state? That could have tripped the BMS over current protection. If so, how does that get reset?

 

[crashmaster]

It’s probably good the second battery never connected once your first battery was at a significantly lower state of charge. The battery to battery current would have been very high and possibly overheated the interconnect wires.

I was thinking at the time that it wasn’t too smart of me to let the SOC on that one battery get so low. A thermal runaway would not be good to say the least. Camper, truck, garage and then house on fire.

 

[Jon R]

I was thinking at the time that it wasn’t too smart of me to let the SOC on that one battery get so low. A thermal runaway would not be good to say the least. Camper, truck, garage and then house on fire.

See my edit above that I was writing when you replied.

 

[Jon R]

I was thinking at the time that it wasn’t too smart of me to let the SOC on that one battery get so low. A thermal runaway would not be good to say the least. Camper, truck, garage and then house on fire.

The cells wouldn’t run away thermally - the BMS overcurrent protection and or internal fuse would prevent that. You could burn up your wires, though.

 

[crashmaster]

Thanks Jon, that’s good to know. I was thinking that wasn’t one of my brightest decisions of the day. ?

I connected the batteries when they were both at 100% SOC, fully balanced according to the BMS app. Voltages were slightly different, #1 was 13.6V #2 was 13.9V.

 

[crashmaster]

I got an email response today that makes some sense: apparently English to Mandarin and back to English communication has been more problematic than I expected. Here is the first response I got 2 days ago.

“
Pls do not worry, this is a normal phenomenon. Let me explain for you.
When designing the LiTime Bluetooth battery, we focused on enhancing its ability to handle system surges by improving and balancing the BMS current collection accuracy and sampling range.
And finally, this allows our battery to accurately collect high currents of 500A or more, as well as currents as low as 1A.

When multiple batteries are connected to one battery system, the discharge current for each battery will be distributed according to the internal resistance of each battery. If the system is discharged at a lower current, it may affect the accuracy of the State of Charge (SOC) display for batteries discharged below 1A.
And this does not impact the actual capacity or functioning of the system. ”

Here is another response I just got this morning after I said I don’t think they understood the issue.

“You may misunderstood. Two Bluetooth batteries can certainly be used together in parallel. You just need to connect the batteries in parallel. And set up 2P1S on the app.

As we have explained, it is normal for two batteries to show 50% on one and 100% on the other. It does not mean that only one battery is being used. You can refresh and recalculate the State of Charge (SOC) by connecting a larger load and performing a cycle of full charge and discharge on the battery system.
You can set 2P1S through the app, so that you can see the whole battery system information on the app. The discharge should be monitored with the page of the whole battery system as reference.”

After 4 days of back and forth this was the first mention of anything needed to be done on the BMS app. Or any mention that the app had such a setting. I did not find any mention of this on their instructions for connecting their 2 batteries in parallel. I still don’t quite understand why I have to put a higher load on the battery but I will ask them how high a load needs to be put on it. I thought around 5 amps would have been enough.

Naturally this morning I had to leave town for work the next two weeks but when I get back home I will find the place to adjust the app, try it out and post the results.

 

[Vic Harder]

How big is your inverter? I have a 3000W Pure Sine inverter and can load it up to a 200A DC draw if I run my induction cooktop and an electric heater at the same time. If you can do something similar, that should be a big enough load I would think

 

[crashmaster]

I have a 1500W inverter I could put on it. I still don’t quite understand why I need to put a big load on it. From the emails it sounds as if anything over 1 amp would be enough. It shouldn’t be such a project to just wire 2 batteries in parallel and use them. ?

 

[Vic Harder]

You are correct, it should not be hard.

 

[sphagnumsprite]

I have the same parallel setup in my van and I see the same thing happen. Notably when the app reports one of the pair in "standby" 99% (batteryA) and the other in "standby/Full" 100% (batteryB ).
When I start up my fridge, often A discharges and B stays in "standby/Full". B supplies 0 Amps. Before I learned to catch this problem I saw A deplete to 18%, while B remained at 100%, before I decided to plug in.

I am alert to this now. My solution is to use the app's "discharge switch" for battery A, to turn A off. Then B starts to discharge. I just turn A back on, and they both discharge normally. They maintain any SOC offset, more or less, as they discharge. Each battery then supplies about half the amps demanded, as expected.

Li Time avidly tried to help me with this, even to ask how many amps my fridge demands, but I could not understand their explanation or answer. I do NOT believe both batteries are discharging when this happens. I think the reporting is accurate. The BT monitors are independent. I think the BMS programming is flawed in "standby/Full" mode, and possibly there is some other corner case where this behavior is beneficial.

When my fridge runs it takes about 5A. The B hold-out battery is always the same one of the pair. The problem doesn't seem to occur when I start up the fridge when the batteries are not fully charged. Li Time made noises about the fridge being too small a load for me, too. I did try a bigger load than the just fridge (7.4A), and this still happened.

I am thankful I can monitor these batteries. I can see what is going on, and I now know I can catch this early. Without the bluetooth I would never have insight into what the batteries are doing. I'm quite happy with this upgrade from AGM. Figuring this out was confusing, but wiring up monitors would have been impossible for me.

I hope my solution can help you.

 

[Jon R]

Aside from the annoyance of unbalanced batteries in my bank, from a safety standpoint, I wouldn’t want unknown software logic and unknown hardware to be the only thing preventing the connection of a fully charged 100 ah battery to a near-fully discharged 100 ah battery in my camper. I would not simply be satisfied with that same unknown software being stated to have overcurrent protection. I think if I kept those batteries to use in a parallel network, I’d put an 80 or 100 amp fuse between them.

 

[crashmaster]

I have the same parallel setup in my van and I see the same thing happen. Notably when the app reports one of the pair in "standby" 99% (batteryA) and the other in "standby/Full" 100% (batteryB ).
When I start up my fridge, often A discharges and B stays in "standby/Full". B supplies 0 Amps. Before I learned to catch this problem I saw A deplete to 18%, while B remained at 100%, before I decided to plug in.

I am alert to this now. My solution is to use the app's "discharge switch" for battery A, to turn A off. Then B starts to discharge. I just turn A back on, and they both discharge normally. They maintain any SOC offset, more or less, as they discharge. Each battery then supplies about half the amps demanded, as expected.

Li Time avidly tried to help me with this, even to ask how many amps my fridge demands, but I could not understand their explanation or answer. I do NOT believe both batteries are discharging when this happens. I think the reporting is accurate. The BT monitors are independent. I think the BMS programming is flawed in "standby/Full" mode, and possibly there is some other corner case where this behavior is beneficial.

When my fridge runs it takes about 5A. The B hold-out battery is always the same one of the pair. The problem doesn't seem to occur when I start up the fridge when the batteries are not fully charged. Li Time made noises about the fridge being too small a load for me, too. I did try a bigger load than the just fridge (7.4A), and this still happened.

I am thankful I can monitor these batteries. I can see what is going on, and I now know I can catch this early. Without the bluetooth I would never have insight into what the batteries are doing. I'm quite happy with this upgrade from AGM. Figuring this out was confusing, but wiring up monitors would have been impossible for me.

I hope my solution can help you.

Thats very helpful. Thank you. When I have the batteries wired in parallel, the discharge switches do not work on either of my batteries. I’m sorry to hear that there may be no real solution to the problem. I’m going to try the app setting they recommend for wiring in parallel, and if it’s still a problem, I will attempt to send them back for a refund. There are a few reviews out there that said LITime would not make good on their warranty. Unfortunately it sounds like the standard case of buy cheap Chinese stuff, buy twice.

The only issue I have with my 6V AGM’s is that they only lasted 6 years. Other than that, they far outperformed the LiTime batteries.

 

[sphagnumsprite]

Jon R, I see what you are getting at. What wire would be "between" the batteries for installing a fuse?

 

[sphagnumsprite]

Thats very helpful. Thank you. When I have the batteries wired in parallel, the discharge switches do not work on either of my batteries. I’m sorry to hear that there may be no real solution to the problem. I’m going to try the app setting they recommend for wiring in parallel, and if it’s still a problem, I will attempt to send them back for a refund. There are a few reviews out there that said LITime would not make good on their warranty. Unfortunately it sounds like the standard case of buy cheap Chinese stuff, buy twice.

The only issue I have with my 6V AGM’s is that they only lasted 6 years. Other than that, they far outperformed the LiTime batteries.

I have had trouble with the software discharge switch not working. If I truly exit the app and restart it from scratch, then the switch begins to work.

I also deleted the parallel "battery system" that I first set up in the app. I feel that is only a representation of the layout, and doesn't have any affect on the battery behavior. I'd like to know if I am wrong.

I have written to Li Time about the safety issue Jon R raised.