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My project is currently tracking to a ~600V pack with 160 cells in series (80 leaf modules). I'm trying to figure out a reasonably priced basic BMS system that will perform exactly two functions:
- cell charge balancing
- cell undervoltage protection

This is one of the lower cost options I have found: https://www.aliexpress.com/item/32945565819.html

Is this the best budget option for a pack with this many cells, for basic protection and charge maintenance?
 

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In order of best to least-best (a highly subjective process)

ZEVA (8/10) - a solid product and very well integrated. It also has full integration with TC chargers so you can adjust voltages and currents with ease. Only scores a 8 because there can be no 10. Why else would people still be working on a better BMS? Not cheap, but worth every cent. Pros - reliable, robust and very informative. Cons - Runs everything on CAN bus. If you aren't familiar with CAN it can be like sitting an exam in Swahili.

EV-Power (7.5/10) - a solid product but still in beta. It's a delightfully simple BMS with simple settings and functions. No charger integration other than a switched output (un-enabling a charger, for example). Quite compact and really quite affordable despite its limitations. The screen interface is painfully slow, but you don't really need it for the most part. One problem at the moment is it's limited to 48 cells per master board, so if you want to manage 96 cells you need to use two master boards and put the switched outputs in series. Pros - simple, analog. Cons - simple, analog.

Batrium (7/10) - a solid product, but I think it's too complex. On functionality it's as good as the ZEVA, but more expensive and has lots of fruit you really never use (who needs wireless bluetooth reporting of cell voltage differentials integrated with temperature?). The footprint of the components is quite restrictive as to what cells you can conveniently mount it to. Where space is no problem, this is a good choice; probably why so many DIY Powerwall guys love it. Pros - all the fruit. Cons - All the fruit. Also a bit susceptible to EMI.
 

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Discussion Starter #3
Thanks for the advice!

I think anything that requires a proprietary per-cell bolt-on unit feeding to a central controller gets too expensive too quickly. The batrium products for example run about $35 per leaf module -- that is more than half the cost of the module!

I really need a solution that scales to a very large number of cells with greater cost efficiency, which is why I am looking at the multiple cell units.
 

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My project is currently tracking to a ~600V pack with 160 cells in series (80 leaf modules). I'm trying to figure out a reasonably priced basic BMS system that will perform exactly two functions:

- cell charge balancing

- cell undervoltage protection



This is one of the lower cost options I have found: https://www.aliexpress.com/item/32945565819.html



Is this the best budget option for a pack with this many cells, for basic protection and charge maintenance?
Balance only, and no indication can handle 160S
 

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In order of best to least-best (a highly subjective process)
Great summary of exactly the kind of thing we need to be archiving and presenting to new members.

When I get around to not being too burnt out to collimate a new DIY EV guide, I'll include that info.
 

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Depending on the application, is cutting out a few 100$ really worth it in the long term.

"Buy once cry once" Is my favourite motto, specially on custom vehicles and builds. Do it right the first time or forever be stuck fighting it.

A BMS is the most important part in an electric vehicle, so why cut corners there. You need something you can rely on working always as you will leave it alone to make sure you do not have the battery self destructing.
 

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Heh there is one tough BMS. It is completely analog and works without any user interface. I replaced like 3 BMS but this one stays with me.

- per cell design, boards per 8cells were built
- Analog voltage measurement, each cell has its own measurement diode.
- up to 0.6A balancing per cell. it can be even 2A, however i consider anything over 0.6A fire hazard inside enclosed space.
- LV alert sensor per cell is connected to opto which triggers daisy chain and puts the car in turtle mode.
- HV alert can be added with option for "single cell balancing" signal and/or "every cell balancing" signal to the second opto.

https://openinverter.org/forum/viewtopic.php?f=13&t=209

In fact i dont use all cell HV alert since i set my charger a bit lower than per cell balancing point is. This way i charge up to 4.00V per cell and balancing is done at 4.05V per cell. I dont go over 4V per cell. There is only like 6km of range from 4.00V to 4.20V and i dont want to harm my cells.

I spend some time measuring cells with and without load and i found voltage difference disconcerting untill i performed "full empty" test. I have seen then that most cells hit 3.0V together so it didnt pose an issue anymore.
Right now i just dont care of the voltage my cells are at unless it is LV alert.

If you are interested i can draw any configuration of cells per board.
 

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Discussion Starter #10
Where did you get those boards made? Did you solder yourself?
I'd love a drawing for 24 cells per board. Thanks!
 

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Where did you get those boards made? Did you solder yourself?
I'd love a drawing for 24 cells per board. Thanks!
Yes i draw them in designspark. Then i send drawing for manufacture and finally i assemble them and test sensoring on my 18650 model. All modules are connected and then i disconnect one positive line from the cell and i add my PSU inline. I regulate voltage by adding PSU voltage and i observe HV balancing point.
Because it is analog system this works to 0.03V difference, but i consider that precise enough for everyday use.

This circuit can be made smaller by replacing TO transistors and resistors with SMD. But it is enough for me and DIP components are easier for DIY assembly.

EDIT: I can draw 24S, but i think it would be better to connect them 12S one over the top. Less wasted planform. I decided to stagger them a bit so every level can burn 0.5A and not interfere with the upper level.
How does your cell config look? Can you post a photo?
 
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