What BMS is good for 2-24v batteries in series?

Speedr56

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I want to build 2- 24v 8s batteries and place in series for 48v 280ah. Batteries must be movable hence 2-24v any suggestions?
 

Ampster

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I am happy with my 4S Overkill BMS and especially the support. I thought they sold an 8S version, but you can find it under JBD on Alibaba. It has a temperature sensor and configurable parameters. It can be monitored via Bluetooth with an Android or IOS or USB serial with a PC. Specify which one when you order. Maybe someone else knows of a US distributor.
 

Dzl

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I want to build 2- 24v 8s batteries and place in series for 48v 280ah. Batteries must be movable hence 2-24v any suggestions?

Are you sure you mean series?
Two 8S/24v batteries in series = 8S + 8S = 16S = 48v.
Do you mean two 24v batteries in parallel?
If so that is much more common arrangement.


Some popular options for 8S:

1. Daly BMS (upto 150A separate port, upto 250A+ common port)
2. JBD Smart BMS (upto 100A)
3. Ant Smart BMS (upto 320A I think, but I'm super skeptical of that rating)
4. Chargery BMS (Not current limited)
5. SBMS0 (Not current limited)
*Ordered roughly from simple and/or basic <---> complex and/or sophisticated
 

Speedr56

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Everything I've read says don't put lithium in series, so my plans have changed. I wanted to be able to move 2-24v 280ah batteries separately. I have a 48v inverter so I must go with a massive 48v 16s 280ah 80 + kg monster. I miscalculated my needs and ordered a 48v 100ah battery from China that is too small. I plan on doing a Will P. and tear it down online. I want to make 2- 24v 100ah batteries that I can connect in parallel for a 24v 200ah battery.
 
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Speedr56

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Sounds crazy I know. I plan on running 120v ac for a refrigerator and 5000 btu window air conditioner in my trailer with the 48v system and all low voltage power will come from the 24v system.
 

Ampster

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Everything I've read says don't put lithium in series, so my plans have changed. I wanted to be able to move 2-24v
I haven't read the same things. I have 16 cells in series and the operative issue for me was the advantages of 48 volts. Were the specific reasons those things you read said don't put them in series? I drive two EVs that have a bunch of Litbium batteries in series and parallel.
 

Speedr56

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I am still learning but this seemed legit.


So why can’t Lithium batteries be connected in series?

It’s not recommended to install Lithium batteries in series because when a Lithium battery is charging, the BMS is actively controlling the charge to the cells within the battery.
The BMS prevents the cells from over-charging, balances the cells and performs other tasks to ensure that the batteries are maintained correctly. Once the cells are fully charged, the BMS will go open circuit to prevent further charge going into the battery. This stops the battery from becoming over-charged. When Lithium batteries are connected in series and this occurs, the charging circuit is broken and the charger will stop charging the batteries.
The battery that first gets to this state will be fully charged while the other batteries in the series string will not be. The remaining batteries will be unable to continue charging due to the single battery having gone open circuit.
If you are going to series connect Lithium batteries, we recommend putting one BMS over all the Lithium batteries in a series which will control the charge to each battery and ensure all the BMS’s go open circuit at the same time, preventing any single BMS from completely stopping the charging circuit.
However, we strongly recommend to avoid series connecting Lithium batteries. We instead recommend using Lithium batteries that are designed and manufactured to the required system voltage.
For example, a 24V 100Ah caravan battery system could be built by utilising 2 x 24V 50Ah batteries in parallel or a single 24V 100Ah battery. However, we do not recommend using 2 x 12V 100Ah batteries connected in series. Once these cells have been built, they can be safely connected in parallel to add up to the required capacity. This way, you’ll always have full control over the voltage.
 

Dzl

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I haven't read the same things. I have 16 cells in series and the operative issue for me was the advantages of 48 volts. Were the specific reasons those things you read said don't put them in series? I drive two EVs that have a bunch of Litbium batteries in series and parallel.

Ampster I believe he is referring to stacking two 8S DIY batteries in series as opposed to your 16S setup.

I have no knowledge of whether this is advisable or not, or how to best accomplish it, obviously many Drop-ins do it, but I don't know if anything special is going on between the BMSes, do you? It seems like the BMSes could potentially conflict with eachother or trip over eachother in a number of ways but haven't thought that through.
 
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Dzl

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I have a 48v inverter so I must go with a massive 48v 16s 280ah 80 + kg monster...
...
I want to make 2- 24v 100ah batteries that I can connect in parallel for a 24v 200ah battery.

I don't understand why you would need both the 24v and 48v system in the same trailer? or are these for two separate projects?
 

snoobler

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Doesn't seem to have a problem with it, with the following exception:

" *If you plan to wire your batteries in series, please let us know when you place your order so we can make sure to match your capacity. "

If you top balance all cells and both batteries prior to deployment, and they have their own individual BMS, I would expect problems to be minimal.

16S with one BMS would be better.
 

Ampster

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but I don't know if anything special is going on between the BMSes, do you?
Yes the issue they raised was if one BMS disconnects, then the whole pack goes down. The best way to manage a pack is to manage voltages such that the BMS shutdown is a last resort. With drop in batteries that is not as easy to do. Drop in batteries have to rely on the BMS shutting down to protect the manufacturer from claims. It is a different philosophy. .
16S with one BMS would be better.
I agree, there is a way to allow the packs to be disconnected and the BMS wires to make the packs moveable.
 

Speedr56

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I don't understand why you would need both the 24v and 48v system in the same trailer? or are these for two separate projects?

I screwed up. Wrong calculations in my original plans. I will have the spare parts including pv panel, 16- 100ah cells and 30a inverter may as well use it and a grand total of 3k in batteries and bms'
 

Dzl

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Can anyone point to an example of someone doing this?

I don't recall seeing it done before, DIY packs in parallel is relatively common, but DIY packs in series, I don't believe I've seen.
 

Speedr56

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yes, DIY battery packs with individual cells, not a drop in like Battleborn.
 

Dzl

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I dont believe the OP is doing that either. He referred to a DIY pack article as an example of why not to series Lithium cells.

I may be misunderstanding you, or you may be misunderstanding me or both. To clarify:

I believe OP wants (or wanted) to build 2 x 8S DIY packs, and then put them in series for 48v.

From the original post:
I want to build 2- 24v 8s batteries and place in series for 48v 280ah.

This is not something I have seen done before as a DIY project (but my experience is rather shallow), I have seen it done with Battleborns and maybe other drop-ins.

My question was whether anyone has seen or can point to an example of what OP wants to do "8S2S" (specifically with DIY packs / commodity BMSes).
 
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Ampster

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I may be misunderstanding you, or you may be misunderstanding me or both.
I reread this entire thread and it is littered with typos and changes in direction.
To be clear I was initially trying to find a solution for the OP who wanted a 48 volt pack that he could split in two in order to transport it to another location. Ultimately I agreed with @snoobler that a 16S BMS would be better.
The article from Valence was talking about their Drop In pack not being in series. I made a typo and referred to the Valence article as a DIY pack. I have not seen an example of two DIY 8S packs each with their own BMS successfully put in series.
 
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ArthurEld

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I'm surprised that it isn't common to make 12v battery packs that are easy to move around. Then connect them together to make a 24v or 48v.
I assume we could use separate BMSs for each 12v pack and then another BMS to connect them together for 24v or 48v.
 
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