16s BMS advise

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400bird

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Apr 27, 2020
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I am looking for a BMS to run a 16s lithium (~3.7 volt cells) pack

Ideally it could remote trip a breaker/control a relay. But one that breaks the current internally would do if rated at something like 40 amps continuous.

Adjustable voltage cut off would be nice, but not necessary.

This is just temporary to get cell testing done. I haven't managed to find a 16s balance/charger one like you can find for smaller packs.

So I suppose price and reliability would be the highest concern. Any recommendations for a cheap 16s BMS?
 

400bird

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Thank you
I was not familiar with energus

I didn't see current transducers on their site. Where/what did you source?
 

400bird

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Thanks!

Is this version the same thing, just with the display integrated into the main unit?

https://www.ebay.com/itm/Smart-300A...attery-Protection-Chargery-BMS16/193273995213


I should have specified I was looking for cheap as the highest priority. I need some time to get the factory BMS working and communicating and verify function. I plan to repurpose modules from BMW 740e and hopefully the i3 CAN messaging is similar enough that with some work, I can get something like simpbms working. Or give up and go with a batrium...

Either way something like this might fill in for me while figuring out the rest.
I will have 6 16s modules, so that's 6 separate BMS's. So I would order 5 cheapos to run while testing the 6th module.
https://www.ebay.com/itm/Smart-300A...attery-Protection-Chargery-BMS16/193273995213
 

OffGridInTheCity

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400bird said:
Thanks!

Is this version the same thing, just with the display integrated into the main unit?
https://www.ebay.com/itm/Smart-300A...attery-Protection-Chargery-BMS16/193273995213
I think itsthe same familybut cheaper than mine - e.g. mine is16TPro and this is16T?. Mine came with a shunt anddisplay separated from the BMS box - but your linkis cheaper! Here's a pic of what I got (+ sense leads I've already soldered into place) butI don't plan to use the shunt -so I like your link better :)

image_qmencv.jpg


I have Batrium as my main house BMS - this is my first attempt to useChargery - e.g. I'm testing it for a 18650 battery for myAPC UPS 3000. There are some good youtubes on it etc and its been around for a while - so I think its the 'real thing'.

400bird said:
Either way something like this might fill in for me while figuring out the rest.
I will have 6 16s modules, so that's 6 separate BMS's.
I'm not sure what you need - e.g. are all 6 modules seperate or do they form a battery bank or ?
If its 1 battery bank (of 6 x 16s modules), you can parallel the balance leadsof all 6 modules into just1 BMS. This particular BMS puts out 12v for a relay control of the load - so you can by a big relay to cut-off the entire battery. This BMS does a respectable 1.2a per cell - and it would balance 6 modules in parallel if you weren't in a hurry.
 

jonyjoe505

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the smart300a (109 dollars) is the chargery bms16, from the ebay link it comes with the 300 amp shunt. It has all the parts needed except the contactors/relays, on mine I just use the cheap 4 dollar 30a automotive relays.

Since you have 6x separate 16s packs, all you need is one bms and parallel all the packs together, connecting all the balance connecters to each other so the battery will equalize. As long as the batteries are the same voltage when you connect them together it will work.

Chargery is a very good bms, I been using since last year, fully programmable. Will easily handle your 16s pack.
 

400bird

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Yes 6 separate 16s packs. From an EV, just ready to drop in and wire up a BMS


Really? Parallel all the balance leads together and run 1 BMS?

That sounds great!
I had considered this but, my concern was that in the case of a cell failure, I might end up passing current through the balance leads from one module to another. The OE balance leads are tiny and would burn up easily. Then the BMS wouldn't be able to detect the fault and open the contactor/breaker.
 

OffGridInTheCity

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400bird said:
Yes 6 separate 16s packs. From an EV, just ready to drop in and wire up a BMS


Really? Parallel all the balance leads together and run 1 BMS?

That sounds great!
I had considered this but, my concern was that in the case of a cell failure, I might end up passing current through the balance leads from one module to another. The OE balance leads are tiny and would burn up easily. Then the BMS wouldn't be able to detect the fault and open the contactor/breaker.
This topic has come up a few times and (surprisingly to me) a key observation by senior folksis that the 'raw current' will flow thru the charge/discharge wires and not thru the parallel/balance leadsexcept under extreme conditions. So what are those extreme conditions and and how can you handlethem... that depends somewhat on the type of cells you have. For example,

- one 'extreme condition' is that the balance leads short-out - this can be handled by using good wire/practices.
- another is you parallel batteries that are wildly different SOC from each other - obviously they should be put in a similar state of charge/voltage before hooking balance leads together.
- another is 1 of the batteries burns up from external fire? - then temp sensors may be the answer.
etc etc...

You say - "... in the case of a cell failure, I might end up passing current through the balance leads..". I'm not sure what kind of cell failure you're thinking of. An 18650 cell might fail and become a dead short - but fuse wires handle that. A cell might start self-discharging... but this will be gradual and will pull the others down and the BMS willdetect it.

Can you share the exact cellsin your EV batteries? And maybe more about what you'rethinking when you say 'cell failure'?
There are indeed things to consider - but perhaps it can mitigated with techniques you should do anyway.

And maybe @Daromer will comment here :)
 

400bird

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I am surprised that the concensus is that it works fine to parallel balance leads. I do automotive electrical work every day and will ensure the wiring is done right and tidy.

My concern is about a weak cell. The parallel cells in other modules would try to push some current through the balance leads when the weak cell's voltage dips under load. I should say dips more compared to the healthy cells. That voltage differential could push enough amps to burn up the tiny or balance lead to the weak cell. Now that cell is unmonitored and getting weaker without any way for the BMS to alarm and shut off the current.


The battery would be from a BMW 740e 9.2 kw
That is 6 modules of 16 cells each. I haven't found any data to say if the "cells" are actually parallel cells inside each "cell" casing.

Or some other production EV (Chevy Volt)
 

gpn

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I'm using a chinese smart bms with two packs connected and the balance leads paralleled. The packs at 15s17p. My plan is to expand because I can still get more of the same packs. Each one is about 2kwh, give or take. But when I expand I plan to move to the DiyBMS which you can program up to 4 "banks" of up to 16s per bank. So that way each cell will be monitored and reported better giving me better insight into the packs.
 

OffGridInTheCity

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400bird said:
My concern is about a weak cell. The parallel cells in other modules would try to push some current through the balance leads when the weak cell's voltage dips under load. I should say dips more compared to the healthy cells. That voltage differential could push enough amps to burn up the tiny or balance lead to the weak cell. Now that cell is unmonitored and getting weaker without any way for the BMS to alarm and shut off the current
You want to*start with* healthy batteries/cells. If you have an unhealthy cell/battery you shouldn't use it - regardless of BMS.

When you start with healthy batteries/cells, that are charged closely to each other before paralleling- the situation you describe would be a gradualdip/self-discharge over time as the battery agesand the BMS will catch it. Voltage differences of <=100mv (0.1v) between cellsare no big deal and willnot cause significant current. If it gets to be 1000mv (1.0v) over timeits a bigger deal but aBMS can detect this and its not as much current as you might think.

The Chargery 16 has a customize-ablesetting for 'Diff of Cell Voltage' - with a default of 300mv (0.3v) - that you can set to trip the relay long before this becomes a 2.0v difference and current becomes an issue.

FYI - here's a youtube done by @Daromer,one the forum's most technical/senior members on this topic: Installing a smart BMS on a 14s LiIon battery packhttps://youtu.be/sGj9UrfEcAw

Now, the downside of paralleling 6 batteries into 1 BMSis that it won't tell you *which cell* (of the 6 in parallel)is self-discharging. But again, this should not occur until a battery starts to become unhealty. The upside 1 BMSs per battery -it will focus on the 1 battery. If your batteries are healthy then maybe parallel all 6 for now and save up for seperate BMS(s) or a Batrium whichcan monitor a lot of cells independently of the number of batteries.
 

Redpacket

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If you're worried about paralleling the balance leads for cell short type failures, you could fuse them....
The balance leads on many BMS systems are deliberately thin so they act as the "fuse", eg Batrium
 

OffGridInTheCity

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Was just watching @DavidPoz's latest youtube - and notice the Chargery 16 (blue box) BMS and nest of red wires to the right in the beginning of the video. He's got several, paralleledbalance/control leads coming off that stack of LifePO4 units powering his house. Just a bit more proof that its for real that you can parallelize a group of large batteries/cells.

Off Grid SMA Sunny Island Inverter Wiring, 48v DC

If you go back a few months in his videos you can see the wall of batteries and good detail of how he hooked them up.
 

floydR

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How are you testing each 16s module?
You don't want to break up the 16s modules which I understand.
Have a volt meter connected to each module? if one meter is lower then the other volt meters you have a weak cell in that module. The balance wires would essentially be cell level fuses like in a 18650 based battery. Each module could be fused.

Later floyd
 

400bird

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Cell level fuses, when they blow, remove the current path from that cell. When parallel pack balance leads fail, the cell is still in the current path and the BMS doesn't have any way to monitor that cell.

I understand that one BMS with parallel packs would work under most circumstances, but we don't use a BMS to protect from "most" failures. I fell like at that point why even run a BMS?

Plan for module testing is use the inverter for a full charge/discharge cycle with the BMS connected. I may end up using a different load and/or charger. But, I don't have the components yet. Still planning, the more I plan the less likely I am to make the wrong purchase or miss some detail.
 

OffGridInTheCity

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400bird said:
Cell level fuses, when they blow, remove the current path from that cell. When parallel pack balance leads fail, the cell is still in the current path and the BMS doesn't have any way to monitor that cell.

I understand that one BMS with parallel packs would work under most circumstances, but we don't use a BMS to protect from "most" failures. I fell like at that point why even run a BMS?

Plan for module testing is use the inverter for a full charge/discharge cycle with the BMS connected. I may end up using a different load and/or charger. But, I don't have the components yet. Still planning, the more I plan the less likely I am to make the wrong purchase or miss some detail.
You don't fuse balance leads. Fusing is forindividual 18650 cells as they join the bus is to protect the pack (not the cell or balance leads) in case of catastrophic 18650 cell failure to a dead short. Cell fusing is not standard for Chevy EV cell hookups that I've seen - they are fundamentally different physical design (pouch) as compared to 18650 and larger/fewer in a battery as compared to many/smaller 18650 cells.

I sense that you're skeptical ofparallization of cells in multiple batteries and that's perfectly fine.The point of this thread is just toshare that it's a validtechnique to consider - butthat doesn't mean its rightfor your situation. :)
 

floydR

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The cells would still be connected via the positive and negitive buses. I mispoke when i said the balance leads would be like cell level fuses. All a fuse in the balance wire would protect is the balance wire. The volt meter on each module would let you know which module has a low cell/high cell if you checked them.

later floyd
 

400bird

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Thanks for the help everyone. I'm going to order a chargery bms16. With this I can at least get each pack tested.

You are right, I am uncomfortable using just one BMS. But, I don't yet know what I will do.
 
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