Is BMS really necessary?

ebike11

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Regarding battery packs that are being built from scratch?
I mean if we can set the cut-off limit of the charger and also to controller or Cycle analyst then I think
it should be sufficient correct?
Of course BMS does add battery protection
 
Yes and no. Depending on the cells chemistry and the use you give to them.
You can have the lvc from the controller and the hvc from the charger. If you do not discharge to the limit and also you charge with a little margin, let's say 4.10 or 4 instead of 4.2 you should be safe but that depends on how stable the cells are. You must know it before picking the cells. Sony konion are a good option for a bms-less battery. Really stable and tend to self balance.
If you doubt put balance leads so you can monitor the cells and balance them with a rc charger if needed. Balance leads are always a better option than a super cheap or non reliable bms.
 
It might also be an option to run a balancing RC charger once every dozen charges, and a simple bulk charger to only 4.1V per cell on a daily basis to provide a safety margin.

If you try that, please keep records and report back how it goes and any issues that arise.
 
ebike11 said:
Regarding battery packs that are being built from scratch?
I mean if we can set the cut-off limit of the charger and also to controller or Cycle analyst then I think
it should be sufficient correct?


well if you have perfectly identical cells and perfect pack electro-mechanicals, then yes you could be without a BMS

more realistically, if you get all your cells from the same batch, don't draw too much current from them, and have very low resistance electrical connections between cells, then you could expect to not have to balance for months (or more).

however if even just 1 cell goes bad, or if even just 1 connection fails, then you have a dangerous situation

personally i'd rather trust my own work than to rely on a BMS that may fail. so most of my packs have no BMS. but all have a port for monitoring:

B7gI0SG.jpg
 
Yes, a BMS is always mandatory.

But it may or may not be a machine. If you run your battery naked, you are the bms.

Never blindly trust a bms. At least, think about what will happen if a battery fire happens where you stash your bike/vehicle.
 
I'm building a 20s4p samsung 30q 18650 pack for my cyclone 3000w conversion. I ordered a bms from besttech which is physically a bit too big to fit on my frame. I'm thinking a low voltage alarm for riding. Worst case I'll ruin the pack, it's not going to explode through over discharging (or is it?). I thought I might use the bms to charge the pack. Any thoughts anyone?
 
have been using A123 12S packs for years with NO BMS, with no problems.
In my view LiFePo does not need any electronics,
I am and CELLLOGs with LVC are my BMS,
 
I don't use BMS, but I do monitor using CellLog and every once or twice a year I will balance my cells using 1010 icharger. It works great for 36 volt packs. I wont be using any BMS until these units are 100% fail proof or I have a way to monitor the cells. This is one reason I build my own packs and stick to 36 volt packs for now. I really hope future BMS will have a LCD option to monitor all the cells.
 
Some people don't have the mental present to be able to self monitor a pack of cells. You know the person that can never find their keys 4 times a day. By myself don't use a BMS I would only do it on a 15 amp hour or bigger pack. You would have to be wearing out sense wires and monitoring devices I must have 6 different ones. Plus it the quality of the cells and how you use them.
 
In over 20,000 miles of bulk charging with a 50Ah pack, I've seen at most .05 variance. I've swapped out 5 cells out of 120 cells total in the pack, and most of them were still plenty safe to use. The key is, have enough capacity you never run your cells anywhere close to the voltage they start to be at risk. The ones that tend to have fire issues seem to run BMS, or running way too low capacity for their needs, or their wiring practices are horrendous. I bulk charge normally twice a day. work is about 20 miles one way. I don't have to charge to do 40 miles, and do 60 miles on the weekends often on a single charge, but I still don't run down low enough I'm concerned. Run heavier, quality, wire than what your system requires. I used to own a car audio and security business, so wiring comes pretty natural to me, and had cars win trophies in IASCA events.

I'd rather have notice on a display where I can check all 120 cell voltage and battery life capacity percentages. Soon as that comes out I'll be in line to buy it.
 
I am hoping we will see more full controller systems. By that I mean like how Adaptto control both the motor,the charging and the cell balancing. Crossing my fingers for such a solution with the Mobipus 72200 and the Mobipus 72600 controllers. In combination with a large screen that Mobipus supports one could have real time cells status on the display. And check every single cell. Yet the ease of ust plugging in the charger and let the BMS take care of the balancing as well as the HCV.

There are 200-300$ BMS systems out there, for that price one would think they are reliable? Have anyone tested one of the high end BMS's? Worth dropping the savings on such a BMS or rely on manual balancing?
 
MarkLeeds said:
I'm building a 20s4p samsung 30q 18650 pack for my cyclone 3000w conversion. I ordered a bms from besttech which is physically a bit too big to fit on my frame. I'm thinking a low voltage alarm for riding. Worst case I'll ruin the pack, it's not going to explode through over discharging (or is it?). I thought I might use the bms to charge the pack. Any thoughts anyone?
Yeah if ur running that many watts as to over 1000watts then u need to do at least 10 in parallel so the battery can last u at least 1 hour so if it does to quickly it's because ur using too Lil in parallel
 
rborger73 said:
In over 20,000 miles of bulk charging with a 50Ah pack, I've seen at most .05 variance. I've swapped out 5 cells out of 120 cells total in the pack, and most of them were still plenty safe to use. The key is, have enough capacity you never run your cells anywhere close to the voltage they start to be at risk. The ones that tend to have fire issues seem to run BMS, or running way too low capacity for their needs, or their wiring practices are horrendous. I bulk charge normally twice a day. work is about 20 miles one way. I don't have to charge to do 40 miles, and do 60 miles on the weekends often on a single charge, but I still don't run down low enough I'm concerned. Run heavier, quality, wire than what your system requires. I used to own a car audio and security business, so wiring comes pretty natural to me, and had cars win trophies in IASCA events.

I'd rather have notice on a display where I can check all 120 cell voltage and battery life capacity percentages. Soon as that comes out I'll be in line to buy it.

Yeah I agree with this guy i had dropped some of my cells to low if it wasn't for the bms by the time I got the battery home it would've ate & killed nearly half my pack of 52 volts like last 3 times
 
Not wishing to start a new thread with the same subject...

I want to build a battery pack to replace a lead-acid battery for a motorcycle, since there is no electric starter, not much capacity is required. I have some 5,000 mAh LiitoKala 26650 cells from another project. My plan was to just put 4 in series to give me a 14.8 volt pack. It will be charged from the alternator with a series pass regulator which will keep it at or near that voltage. There is nothing critical in the voltage, most if not all bulbs will be LEDs

I have ordered a 4S BMS, but it will take a while to get it, is it really necessary to run one in this application? I am basing my doubts about a BMS being absolutely required on a BALISTIC battery I opened which is made up of 8 Lipo 26650 cells in a 4S2P configuration without any BMS, all it has is a 5 pin connector to connect to one of their own chargers that has a BMS inside (I think) but for day to day use, only the main terminals are used.

So to BMS or not to BMS, that is the question!

Jean
 
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