2 LiTime 100ah Bluetooth LiFePO4 in parallel

[crashmaster]

I did follow the instructions, zeroed the setting before each measurment. However after zeroing the measurment I can see it fluctuate 0.2 to 0.4 amps by simply moving it around, so I made the assumption that the 0.42 variance I saw in my measurments of the battery system was based on errors possible from moving the meter itself around the wire in the clamp.

The BMS did confirm that 4.2 amps was coming from battery #1, and battery #2 had 0 current and was in Standby, much like the images on my first post on page 1

If you flip the clamp meter around on the wire, a positive number will then show negative, and vice versa. this is current flow.

My measurments show current flowing from the #1 battery to the #2 battery, and the same amount of current flowing from battery #2 to the camper. Given that, all current is coming from #1 battery, and 0 from #2 battery, which is also shown on the BMS of each battery as well.

 

[Jon R]

I did follow the instructions, zeroed the setting before each measurment. However after zeroing the measurment I can see it fluctuate 0.2 to 0.4 amps by simply moving it around, so I made the assumption that the 0.42 variance I saw in my measurments of the battery system was based on errors possible from moving the meter itself around the wire in the clamp.

The BMS did confirm that 4.2 amps was coming from battery #1, and battery #2 had 0 current and was in Standby, much like the images on my first post on page 1

If you flip the clamp meter around on the wire, a positive number will then show negative, and vice versa. I assume the +/- is there for measuring AC current in Load or Neutral. If AC load and neutral wires are both put in the clamp the numbers will cancel each other out. I dont know if the +/- is applicable for measuring DC current.

The plus or minus tells you current direct for DC. For AC, it should give you RMS (root mean square) current, with no sign or direction because it’s alternating direction.

 

[crashmaster]

The plus or minus tells you current direct for DC. For AC, it should give you RMS (root mean square) current, with no sign or direction because it’s alternating direction.

Thanks Jon, I just now figured that out from a little google study about current meters as well and edited my post. Hence in my photos, power is flowing from #1 only and #2 is in standby just as the BMS app indicates for each battery.

So, given this new information from the clamp meter, Elaine from Li Time basically was telling me incorrect information when she said:

<<<Pls do not worry. Two batteries connected in parallel is equalising the voltage.>>>

Unless I have a faulty BMS in one of the batteries, Li Time's Bluetooth BMS will not allow 2 of these 100ah batteries to be used in parallel.

 

[Vic Harder]

Let's ignore the BMS for now and use just the induction meter. You can't know from which battery current is flowing if they are in parallel. So you would have to be measuring the current from each battery separately. I'd still be curious: Leave the meter attached to the left most battery positive lead, but disconnect that lead from the left most battery (not sure which is #1 or #2). Current should drop to zero, natch. But do the same with the clamp on the lead going to the loads.... disconnect the positive lead from each battery in turn. Any changes?

 

[crashmaster]

Thanks for the suggestions Vic.

Not sure I understand exactly how to do what you are suggesting, but I am a slow learner. I will read through it a few more times.

Given the +/- is the direction of flow of the current, doesn’t the meter essentially show which battery the current is coming from?

 

[M1010 Mike]

I am wondering if they are having a problem with the way they are wired together. The way you have it, is how to do this for lead acid so they balance correctly but makes me wonder if the BMS isn't allowing that method.

Instead of the way you have it, run each post to the appropriate bus bar (i.e. each positive post to a common + bus bar, each negative post to a common - bus bar). This way each battery is supplying the bus bar and not going through the other battery.

 

[Vic Harder]

Thanks for the suggestions Vic.

Not sure I understand exactly how to do what you are suggesting, but I am a slow learner. I will read through it a few more times.

Given the +/- is the direction of flow of the current, doesn’t the meter essentially show which battery the current is coming from?

I'm not familiar with your meter, so not sure how that would work. As to how to do what I suggest:
- clamp the meter onto the positive wire going to your loads... like in your first picture posted above.
- take a reading... i.e., your 4A noted above
- disconnect the positive lead from the battery on the right... now you just have the left battery feeding the system...
- take a reading - any change? There should NOT be... If the batteries are functioning in parallel (//) then the other battery should pick up the load dropped by the other battery. If there is, well... that implies the battery on the left is not doing anything.
- reconnect the right battery
- take a reading again... just to reset our conditions... still getting the same current (ie, 4A)?
- OK, now disconnect the leads on the leftmost battery's positive post, but leave them connected to eachother - I would use a short bolt or clamp to hold them together.
- (by the way, what is the blue lead on that post? Temp sensor? And does it change to yellow and then red on that thinner wire with a white label? Where does that go?)
- take your reading. Again, it should read 4A if the batteries are truly in //.
- let us know what you find!

Also, before you despair that your money was wasted, I am curious about how the BMS would work. Let's just say your batteries are NOT functioning as expected when hooked up in //. OK, so how are they functioning?

I wonder if you charged them both up (another thought... do they charge in // as expected?) and then started draining them, from what you have observed we would expect only ONE of the batteries would drain, correct? How far? As in, would it get to 5% SOC (or some other - adjustable? - value) and then the other battery would take over? While not ideal, that would give you your full // AH as expected, just not in the way we would all expect // to work.

I hope that makes sense.

 

[Wandering Sagebrush]

I am wondering if they are having a problem with the way they are wired together. The way you have it, is how to do this for lead acid so they balance correctly but makes me wonder if the BMS isn't allowing that method.

Instead of the way you have it, run each post to the appropriate bus bar (i.e. each positive post to a common + bus bar, each negative post to a common - bus bar). This way each battery is supplying the bus bar and not going through the other battery.

That’s an interesting Approach. Had not thought of doing it. Wonder if wire lengths between batteries and buses need to be equal (as they should).

 

[Jon R]

That’s an interesting Approach. Had not thought of doing it. Wonder if wire lengths between batteries and buses need to be equal (as they should).

Hi WS. While I share your preference for symmetry in electrical layouts, I don’t think even large differences in the positive and negative wires from the battery bank to the bus bars matter with respect to balancing battery current. With the battery bank wire arrangement we are discussing, differences in the resistance of the positive and negative wire sections between the batteries would matter and would reduce the current to and from the battery affected by the higher resistance wire. However, I don’t see how a BMS would detect this. Am I missing something?

I’m still wondering if the OP has a battery stuck in a standby mode for some reason. I don’t see how the wire resistance differences due to length differences in the wiring shown by the OP would cause such a large current imbalance on their own or trip a properly designed BMS safety feature. It could also be a bad connection somewhere, but I’ve been assuming the OP has checked for that.

 

[crashmaster]

I'm not familiar with your meter, so not sure how that would work. As to how to do what I suggest:
- clamp the meter onto the positive wire going to your loads... like in your first picture posted above.
- take a reading... i.e., your 4A noted above
- disconnect the positive lead from the battery on the right... now you just have the left battery feeding the system...
- take a reading - any change? There should NOT be... If the batteries are functioning in parallel (//) then the other battery should pick up the load dropped by the other battery. If there is, well... that implies the battery on the left is not doing anything.
- reconnect the right battery
- take a reading again... just to reset our conditions... still getting the same current (ie, 4A)?
- OK, now disconnect the leads on the leftmost battery's positive post, but leave them connected to eachother - I would use a short bolt or clamp to hold them together.
- (by the way, what is the blue lead on that post? Temp sensor? And does it change to yellow and then red on that thinner wire with a white label? Where does that go?)
- take your reading. Again, it should read 4A if the batteries are truly in //.
- let us know what you find!

Also, before you despair that your money was wasted, I am curious about how the BMS would work. Let's just say your batteries are NOT functioning as expected when hooked up in //. OK, so how are they functioning?

I wonder if you charged them both up (another thought... do they charge in // as expected?) and then started draining them, from what you have observed we would expect only ONE of the batteries would drain, correct? How far? As in, would it get to 5% SOC (or some other - adjustable? - value) and then the other battery would take over? While not ideal, that would give you your full // AH as expected, just not in the way we would all expect // to work.

I hope that makes sense.

Thank you Vic for that detailed response, much appreciated. I will try that out and see how everything reacts.

Great thoughts and ideas from everyone, thanks!

 

[crashmaster]

So I have a new little twist in the issue. Last night I started closing and opening the Li Time BMS app on my phone multiple times. After probably about 25 times of closing and opening the app, I was able to get a functioning discharge switch on one of the batteries. I shut it off and turned it on, low and behold, the second battery started supplying a load along with the other battery. However, I noticed the load in that battery switching on and off, going to zero and back up to 2 amps about once every 3 seconds. It did this for about a hour, then went to standby again. All the connections are good. I was able to duplicate it again today. Its does take several times closing and opening the app to get one functioning discharge switch. The cycling on and off of one of the batteries is an interesting twist.

I will keep troubleshooting later this week when I have more time to mess with it.

 

[Jon R]

So I have a new little twist in the issue. Last night I started closing and opening the Li Time BMS app on my phone multiple times. After probably about 25 times of closing and opening the app, I was able to get a functioning discharge switch on one of the batteries. I shut it off and turned it on, low and behold, the second battery started supplying a load along with the other battery. However, I noticed the load in that battery switching on and off, going to zero and back up to 2 amps about once every 3 seconds. It did this for about a hour, then went to standby again. All the connections are good. I was able to duplicate it again today. Its does take may times closing and opening the app to get one functioning discharge switch. The cycling on and off of one of the batteries is an interesting twist.

I will keep troubleshooting later this week when I have more time to mess with it.

Aha! That sounds to me like your BMS is either malfunctioning or protecting you from some real problem in the battery assembly. I would describe that behavior to the LiTime people and ask for a warranty replacement battery.

 

[sphagnumsprite]

Did you ever get a reply about the safety issue from Elaine at Li Time? I am not able to get the bluetooth discharge switches to work when my batteries are wired in parallel, so I was not able to turn one off then on again to see if both batteries would finally take the load.

I have the same experience as you with parallel "Battery System" set up in the app which is essentially lipstick on a pig. It is only a layout representation and has nothing to do with the actual battery conditions as shown by my DC current clamp meter.

The result is that I have 2 batteries that I am not able to use wired in parallel. I have no doubt that the issue is the Li Time BMS. I am trying to return the batteries and get a full refund. I have not heard back from Li Time yet about the refund. Hopefully I get a response by tommorow. If they are avoiding the issue I'm not sure what to do after that.

2 100ah Li Time batteries were $606 USD.
2 100ah Battleborn batteries are $1850 USD.

I did save $1244 over high quality Battleborn units by going with the cheap Chinese Li Time batteries. However I cant use the cheap Chinese Li Time batteries in parallel. Moral of the story, buy cheap, buy twice.

Unfortunately Li Time does not have a good track record backing up their warranty, so likely the tuition for my continuing education is $606.

I got a response from LiTime when I raised the safety issue and pointed them to this post. It was after they asked the same questions about the load at the time of the problem (was it over 1A? -- yes, 5A) and was I charging at the time (no). Here is what I got from Ricket:
-----
The reason why the batteries are discharged in sequence is that the voltages of the terminals of the two batteries are different. The battery with a larger voltage bears all the discharge current first. When the voltage of the battery with a larger voltage drops due to discharge, and the voltage drops to the same voltage as the battery next to it, the two batteries can be discharged together. This is the normal discharge phenomenon of batteries in series and parallel.

Possible questions: The battery APP monitors the battery cell voltage, not the battery port voltage. After the full charge protection occurs, the port voltage will drop by 0.4V~0.7V compared to the battery cell voltage.

After the overcharge protection, the voltage will be 0.5~0.7V lower than the normal full charge voltage;
It has no impact on the normal use of customers, but only avoids the oscillation caused by frequent charging;
-----
The response does not address how one battery ran down to 18% (12.8V -5.8A) while the other stayed at 100% and did not discharge. The say this is "normal"? I'm pretty sure a parallel battery setup free of control by a BMS would not do this.

I don't know if we can't understand each other or if they are obstinately hiding behind the language barrier.

I notice they use the term "full charge protection" and wonder if this is what "standby/full" means. The battery that does not discharge reports it is in this mode. The discharging battery starts in plain "standby" mode, when they are both fully charged, and reporting the same voltage (13.3).

On their point about the voltages: I know the reported voltages are not so accurate because they seem to use a high capacity shunt, but certainly while falling to 12.8V an initially higher voltage battery must match the lower batteries voltage at some point, to allow them to "discharge together", which never happens.

I will try to address this with LiTime. Argh.

With my method of turning off "discharge" on the discharging battery, which wakes up the lax one, I do seem to seem a brief period of one battery charging the other with the app. But as you know, it is only possible to look at one battery at a time, and it takes a while to switch which one is being read. I haven't gotten a meter under there.

The fuse idea is a good one, but hard for me.

 

[Jon R]

I would be running away from that company’s products regardless of what it cost me. Their responses are nonsensical. This is a life-safety related product when used in a confined sleeping space; and everything about their responses suggests to me that they don’t know what they are doing with respect to establishing an appropriate system architecture. In my opinion they should not be trying to manage the parallel loading of batteries with a BMS. They should simply be letting the batteries run in parallel. Any other approach makes you dependent on their logic and switching hardware to avoid huge potential inter-battery overcurrent events.

If they are not acknowledging that the one battery is defective and are defending sequential load application to parallel-connected batteries controlled by the BMSs of the batteries, my advice is not to use this product in a confined sleeping space.

 

[crashmaster]

I got a response from LiTime when I raised the safety issue and pointed them to this post. It was after they asked the same questions about the load at the time of the problem (was it over 1A? -- yes, 5A) and was I charging at the time (no). Here is what I got from Ricket:
-----
The reason why the batteries are discharged in sequence is that the voltages of the terminals of the two batteries are different. The battery with a larger voltage bears all the discharge current first. When the voltage of the battery with a larger voltage drops due to discharge, and the voltage drops to the same voltage as the battery next to it, the two batteries can be discharged together. This is the normal discharge phenomenon of batteries in series and parallel.

Possible questions: The battery APP monitors the battery cell voltage, not the battery port voltage. After the full charge protection occurs, the port voltage will drop by 0.4V~0.7V compared to the battery cell voltage.

After the overcharge protection, the voltage will be 0.5~0.7V lower than the normal full charge voltage;
It has no impact on the normal use of customers, but only avoids the oscillation caused by frequent charging;
-----
The response does not address how one battery ran down to 18% (12.8V -5.8A) while the other stayed at 100% and did not discharge. The say this is "normal"? I'm pretty sure a parallel battery setup free of control by a BMS would not do this.

I don't know if we can't understand each other or if they are obstinately hiding behind the language barrier.

I notice they use the term "full charge protection" and wonder if this is what "standby/full" means. The battery that does not discharge reports it is in this mode. The discharging battery starts in plain "standby" mode, when they are both fully charged, and reporting the same voltage (13.3).

On their point about the voltages: I know the reported voltages are not so accurate because they seem to use a high capacity shunt, but certainly while falling to 12.8V an initially higher voltage battery must match the lower batteries voltage at some point, to allow them to "discharge together", which never happens.

I will try to address this with LiTime. Argh.

With my method of turning off "discharge" on the discharging battery, which wakes up the lax one, I do seem to seem a brief period of one battery charging the other with the app. But as you know, it is only possible to look at one battery at a time, and it takes a while to switch which one is being read. I haven't gotten a meter under there.

The fuse idea is a good one, but hard for me.

Their responses do not reflect our real world experiences. I had the same result as you did. One battery draining to 20% SOC at around 12.8V while the other was at Standby/Full 100% SOC at 13.4V.

I completely concur with Jon's assessment.

My next step is to go though the Li Time refund process.

 

[Vic Harder]

I agree with sentiments posted above…. Don’t buy or use Li Time products based on these experiences. If you are unable to get satisfaction from them, consider that the cells themselves are likely fine, and you could rip open the battery cases, remove their questionable BMS and get a better BMS to manage them.

 

[crashmaster]

I charged up the batteries using a Genius 10 charger. When I started up the fridge, as expected only Battery #1 was connected to the load in the Li Time app.

I let it run down to 93% SOC with the fridge and some other accessories pulling about 5 amps. Then after a few attempts of opening and closing the app, I was able to recycle the discharge switch of Battery #2 that the BMS had in standby. It immediately connected and Battery #2 started charging Battery #1 with over 17 amps of current. Battery #1 current is only showing 6.2 amps because I was not able to open the bluetooth screen quick enough to take the screen shot before the current dropped. You can only view one battery at a time in the app, but you get the picture.

Jon, Vic, I believe your assessments about these batteries in parallel being a potential hazard. Thank you very much for your thoughts and advice in helping me analyze the situation. I'm not sure how much current would be moving if the batteries were connected with one at 100% SOC and the other in 15-20% SOC. It might heat things up?

If I were going to keep these batteries wired in parallel I would for sure wire a fuse between the two. Thats probably prudent with any batteries in parallel in a small confined space like a truck camper. If I use the batteries individually, they seem to work fine.

Li Time says that there is nothing wrong with the Bluetooth BMS and it is working exactly as intended. It is very difficult to understand some of the responses, probably due to language differences.

However, Li Time is giving me a full refund if I am not satisfied with the product, so thats good to know.

 

[crashmaster]

Wiring 2 LiFePO4 in parallel would it be acceptable to use a terminal block and fuse on 1 battery or on both to protect the wire?

Amazon.com

Or is there a better way to do it?

Thanks.

 

[Jon R]

If you have two batteries that do not have a BMS that independently connects and disconnects the cell set from the terminals, you would fully charge both batteries before connecting them, and then connect them without a fuse using a wire size based on anticipated peak charging and load currents plus margin.

If you are trying to protect your wiring if you are going to use those LiTime batteries in parallel, what I suggested was a single fuse somewhere in the interconnect wire between the positive terminals of the two batteries, with that fuse sized to prevent excessive current for the size of wire you selected for that wire. If that fuse opens, it stops the current. You can locate it anywhere in that short connecting wire, and you don’t need a second fuse in the negative battery interconnecting wire.

 

[crashmaster]

Thank you Jon. I’m not using the LiTime. I am going to order different batteries but not sure I really trust the BMS of any of them. So probably maybe just get a Blue Sea fuse block and an 80A fuse for the 4awg wires that I have.

https://a.co/d/inf0Xav

However the positive wires to each terminal will be longer than the negative wires. Not sure if that really matters though.