2 LiTime 100ah Bluetooth LiFePO4 in parallel

[Jon R]

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

A fuse in the positive parallel connecting wire between the batteries is what I am suggesting to limit the current that can flow between the batteries to no more than what your wire size can handle without overheating.

My 200 ah battery has an internal 300 amp fuse as “overcurrent protection.” That’s based on what the cells and internal connections can handle. I don’t rely on that for wire protection for overloads or shorts to ground. I have an external 80 amp fuse six inches away from the battery to protect my 6 awg wiring. I didn’t see what your BMS overcurrent protection limits the current to, but it could be quite a bit higher than your wire size is good for. It also sounds like it’s active BMS protection rather than a passive device like a fuse or CB (I could be wrong about this, though), so it’s likely to be less reliable.

Normally one would balance the batteries in a battery bank before connecting them, and then have one fuse for the positive bank output. In your case, with the batteries having their own ability to turn themselves on and off, the batteries apparently can get way out of balance. Fuses and fuse blocks are relatively cheap.

 

[crashmaster]

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.

I tried exiting and opening the app and still couldn’t get the discharge switch to function with the batteries wired in parallel. They will work if the batteries are not wired together.

I also just sent an email to LiTime about the safety issue. Let us know what they tell you.

 

[Vic Harder]

In a parallel setup, the two batteries are connected to each other with heavy gauge wire, positive to positive and neg to neg. If there is a fuse on either of those heavy wires, it will protect the system from rapid self discharge/disassembly to paraphrase somebody famous.

I would be very tempted to send them back even if I didn’t get a refund.

 

[Vic Harder]

Oh, and a wiring thing: It looks like one battery is the main connection point for both the +ve and -ve wires, and the 2nd battery is just sorta tacked on. You want to wire the batts together with heavy gauge wire, and have all the positive loads on one, and the shunt/negative connections on the other, so ALL current HAS to go through both batts. Make sense?

 

[crashmaster]

I would be very tempted to send them back even if I didn’t get a refund.

I have the batteries wired in parallel with 4awg wires, then the camper positive is on one battery and the shunt/camper negative is on the other battery. If you zoom in a bit on the photo you can see the the 4awg and the negative shunt connection on the separate battery from the positive.

Judging from LiTime reviews on Amazon the possibility of getting a refund from them under any circumstances is slim. Im not inclined to pay to send them back if I don’t get a refund. What I am inclined to do is post my experience with these batteries.

In all likelihood I paid $600 tuition to re-learn a lesson that I already learned once about buying cheap Chinese products. I never did that well in school. ?

 

[Vic Harder]

OK, didn't see that before.

What is your intended workaround/solution?

 

[crashmaster]

Since there is a 4awg attached to each terminal of each battery the camper positive or negative can draw power from the 4awg wire from the opposite battery, correct?

As far as my plan, I’m not really sure yet. Ideally I would somehow convince LiTime to refund at least one of the batteries, which could be difficult. Aside from that I don’t have a workaround.

 

[Vic Harder]

Yes, you are correct. I made a silly assumption and went down a rabbit hole on that one.

 

[crashmaster]

Here is my latest email to LiTime:


<<<The 1S2P setting in the app did not do anything to keep 2 parallel batteries in balance. The batteries are still kept separate by the BMS even though they are wired in parallel with 4awg wire. The batteries still will not connect to each other to stay in balance in a parallel wireing situation. I think this is a big safety issue. Large current could flow from one battery to another potentially starting a fire. Is there another solution to insure the batteries wired in parallel can be balanced?>>>

Here is the response:

<<<Pls do not worry. Two batteries connected in parallel is equalising the voltage. It is also a characteristic of Bluetooth batteries that there is a difference in the SOC display of two Bluetooth batteries. As we communicated before, this can be corrected by adding a load, which is automatically corrected at the next battery cycle.
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.>>>

 

[Jon R]

It sounds like they may be saying the batteries are actually connected in parallel and it’s just the BMS display system that doesn’t work properly. That’s not great, but at least it would mean the batteries are usable.

You could move your shunt around to check this if you have an external shunt. You could also use an ammeter with an inductive probe.

 

[crashmaster]

Thanks Jon.

Would the inductive ammeter be able to determine which battery the current is coming from when wired in parallel? How would I measure that?

 

[Jon R]

An inductive probe for an ammeter is clipped around the wire in which you want to measure current.

You could clip it around the positive wire coming from the battery network to measure total current from the battery under some constant load, and then, without changing the load, clip it around the wire that connects the two batteries to measure the current coming from the battery furthest from the load connection. That second measurement should be roughly half of the first measurement.

If you don’t have access to a meter with an inductive probe there are other ways to figure this out. That type of meter and probe is fairly expensive and is a specialized tool. A Victron Smart Shunt or BMV-712 would be cheaper to buy.

 

[crashmaster]

Would a clamp on like this do the trick?

Amazon.com

 

[Jon R]

Would a clamp on like this do the trick?

Amazon.com

From the specs it appears so, yes. It’s a Chinese-made meter, hence the price, but probably good enough.

 

[sphagnumsprite]

A fuse in the positive parallel connecting wire between the batteries is what I am suggesting to limit the current that can flow between the batteries to no more than what your wire size can handle without overheating.

My 200 ah battery has an internal 300 amp fuse as “overcurrent protection.” That’s based on what the cells and internal connections can handle. I don’t rely on that for wire protection for overloads or shorts to ground. I have an external 80 amp fuse six inches away from the battery to protect my 6 awg wiring. I didn’t see what your BMS overcurrent protection limits the current to, but it could be quite a bit higher than your wire size is good for. It also sounds like it’s active BMS protection rather than a passive device like a fuse or CB (I could be wrong about this, though), so it’s likely to be less reliable.

Normally one would balance the batteries in a battery bank before connecting them, and then have one fuse for the positive bank output. In your case, with the batteries having their own ability to turn themselves on and off, the batteries apparently can get way out of balance. Fuses and fuse blocks are relatively cheap.

Thank you. That is a very clear description.

 

[Jon R]

Thank you. That is a very clear description.

I’m glad it helped, and thanks for the nice feedback.

 

[crashmaster]

I tried a DC clamp meter on the 2 batteries wired in parallel with the fridge and a couple lights running. The first image is showing -4.47 amps from the #2 (left) battery to the camper and the second image is showing +4.05 amps from the #1 (right) battery to the #2 (left) battery.

The #1 (right) battery is taking the load although the two are wired in parallel. Each battery was charged individually to 100% SOC before the were connected in parallel.

I'm unsure why the 2 readings differ by 0.42 amp, but it is a $30 cheap Chinese clamp meter and not a $300 Fluke, so that needs to be factored into the equation.

 

[crashmaster]

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.

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.

 

[Jon R]

I tried a DC clamp meter on the 2 batteries wired in parallel with the fridge and a couple lights running. The first image is showing -4.47 amps from the #2 (left) battery to the camper and the second image is showing +4.05 amps from the #1 (right) battery to the #2 (left) battery.

The #1 (right) battery is taking the load although the two are wired in parallel.

Thanks!

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An inexpensive meter may not have the best absolute accuracy, but it’s relative accuracy when comparing measurements probably should be pretty good. I would assume that those two current measurements you took are fairly accurate and you do have a small amount of current coming from the second battery. This is based on the the assumption that you used the inductive probe in accordance with the instructions.

 

[Vic Harder]

To add to JonR's question, I'm wondering if the BMS was confirming that current was flowing from the battery with that 4A positve flow. That flow could have been going from the rightmost battery into either the left battery, or simply continuing on and that's the measured -4A (why is one negative?

Did you flip the orientation of the meter?).

In other words, you could try removing the wires from the positive terminal of the left battery (join them with a bolt or something) and repeat the measurements on the same wires again.

Ideally, in parallel, there would be 2A coming from each.