# Why the BMS Doesn't Work as You Believe

#### cheez

##### 100 mW

Cheez posts consistently dangerously incorrect information and advice that could lead to fire and death (in regards to batteries, etc).

Other information is simply incorrect and could lead to wasted money and severe dissatisfaction.

Original complete post below:
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There has been massive disinformation about needing for BMS for building battery packs for decades across the whole world.
I want to bring let you guys know that the BMS doesn't work as you believe the way they work.

First thing you need to know, is that you can't measure the voltage of any parallel group cells in a battery pack, except for the very first parallel group (+) and the very last parallel group (-). The BMS can't measure the voltage through these balancing wires connected on the positive side of the parallel groups. It will give incorrect/invalid voltage reading and will trigger the BMS to attempt to discharge and re-charge. The reason why you can't measure the voltage in any of the inner parallel groups of cells is because the positive end you are connecting the wire with is not really positive nor negative because all the groups of cells are interconnected to form a one large single cell. If you pay attention the positive side of the cell is connected to the negative side of the neighboring cell. You are connecting the wrong terminal points to measure the voltage. The only place you can measure the voltage is connecting your wire (or your multimeter probe) to the first parallel group of the cells (+) and the last parallel group of the cells (-). And that is to get the total voltage. You cannot get voltages from each parallel groups because they are all connected to form a one large cell.

Another thing you need to know is that the electricity doesn't travel from one point to another as it doesn't have a direction. They appear instantly when the positive and negative ends are connected. The electricity doesn't travel slowly from positive end of the cell to the negative side of the neighboring cell hoping/assuming your balance wire will "catch" it before it passes to the next cell. Because the electricity doesn't have a direction and appear instantaneously, the voltage cannot be measured. It is like you are attempting to connect the wrong points of the body of a battery cell. The only place you can connect is the very positive end and negative end of the battery pack.

The only time the BMS can "work" is to separate each parallel groups of cells from each other to create their own individual circuit, independent from each other. If you have 4 inner parallel groups you have to create 4 separate circuits. Run the BMS balance wires to those 4 groups of cells and you will be able to measure the voltage on each group, and balance them if needed.

You can also do so by separating those parallel groups of cells and create a sheet of pre-defined conductive metal to place on top of a battery pack and another one for the bottom side of the battery pack to "connect" those parallel groups of cells in series. Fasten these sheets (or board) of metals with screws/bolts and nuts. If you want to measure the voltage of each parallel group cells just lift/disengage the sheets of the metal connectors from the battery. If you re-attach them, you won't be able to measure the voltages on these parallel groups. It is the similar way how the Tesla electric cars are designed for charging their batteries. They have multiple groups of smaller battery packs in their vehicle, has a mechanism to attach or disengage these connections of the battery packs. When charging, they are disconnected from each other, to allow charging. Re-engage for Drive. But balancing the battery packs during charging wasn't the reason for the design of this mechanism but to "safely" charge each and every group of the smaller battery packs with lower voltages and current, as voltage needed to charge one large battery is too much for the battery. They knew that the batteries quickly deteriorate from high voltage stress. They also know the fact that the battery cells connected in parallel and serial in a pack self-balance charge anyway, eliminating the need of BMS or balance charging. The only time the battery cells don't self-balance is when they are run in serial connection-only, but when they are combined with parallel connections they all get self-balanced. Ask Elon Musk about this and he will tell you, which is why he designed the batteries for these cars in such way to charge them without getting batteries get damaged from stress.

So don't just sorely rely on the engineers who made these little BMSs (and any other balance chargers) for e-bikes and scooters because they don't really know how the electricity works in respect to batteries and charging. The only time the BMS/Balance chargers come to use is when you charge the battery cells individually. You can control how much you want drained or charged.

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#### j bjork

##### 100 kW
Just stop with this bullshit, someone might think that you know what you are talking about

#### Chalo

##### 100 TW
j bjork said:
Just stop with this bullshit, someone might think that you know what you are talking about

This.

#### liveforphysics

##### 100 TW
Cheeze- I'm afraid you're badly confused. The purpose of a BMS is to permit the pack to fail gracefully by preventing recharging in the event of an issue arising over the vehicle's lifespan.

Without that functionality, it would be a non-starter to ship products with rechargeable lithium packs.

#### harrisonpatm

##### 1 kW
cheez said:
Another thing you need to know is that the electricity doesn't travel from one point to another as it doesn't have a direction. They appear instantly when the positive and negative ends are connected. The electricity doesn't travel slowly from positive end of the cell to the negative side of the neighboring cell hoping/assuming your balance wire will "catch" it before it passes to the next cell.

Here's my favorite part. Where electrons get to ignore physics in order to Harry Potter apparate into existence wherever you need them.

Electrons are tiny. They move incredibly fast. And it's true that while we can observe their effects, and we have a pretty good understanding of how electricity works, its impossible to say definitively that we fully understand their behavior and the behavior of particles on an atomic scale. The models and theories and explanations of electricity are just that: models. When we say things like "direction of current" and "flow," we are using are limited human language in an attempt to describe something that is essentially beyond our comprehension, but this simplification only works when it is within the format of a somewhat universal system that we can use as a reference point. This is the difference between the theory of electricity and its practice.

But we do know enough to say, no, electrons do not appear instantly. To give you the benefit of the doubt, it is one thing to question our understanding of how things work, and it's necessary to further knowledge, even at a hobbyist level. Do electrons actually travel from one atom to the next? Do electromagnetic fields induce the movement of valence electrons? What is actually happening with current at the atomic level? These are good questions to ask, there's lots of resources out there to explore these concepts.

Please don't say that electrons appear instantly. Some people try to learn from these forums.

#### 999zip999

##### 100 TW
Nobody likes the Cheez . Limburger
Did you know limburger is conductive
Some of the first batteries were made out of limburger ,but to low of voltage. But long life.Till the mice discovers it .
The down side.

#### jskounakis

##### 1 mW
Your post sounds a lot like those conspiracy theories.

Other than that, it's ok I get why someone would feel the need to sound brighter that all those engineers working on BMS, but be realistic man, it can't be that all those EE professionals got it all wrong for some malicious intent...

Cheers

#### cheez

##### 100 mW

Cheez posts consistently dangerously incorrect information and advice that could lead to fire and death (in regards to batteries, etc).

Other information is simply incorrect and could lead to wasted money and severe dissatisfaction.

Original complete post below:
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ebuilder said:
Wow. Quite an indictment of the entire industry.
A question. Do you believe BMS's are useful at all? Or are they completely irrelevant or even harmful?
No, not useful at all.. And yes it's irrelevant as BMS isn't needed for charging electric vehicles/bikes/scooters. The only time the Balance chargers would be useful is you are charging the cells individually to a specific voltage and use them for specific needs.

[mod edit]

Do you dispute that electricity flows from positive to negative? Kind of sounds like it.
It doesn't flow in ANY direction, neither positive nor negative. They appear instantly, takes no time to have electricity to connect between the two terminal points. If you were to run a speed test by shooting a light from a flashlight (or laser beam) from one point to another, the electricity will will form much faster, connecting the two points side by side.

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#### cheez

##### 100 mW

Cheez posts consistently dangerously incorrect information and advice that could lead to fire and death (in regards to batteries, etc).

Other information is simply incorrect and could lead to wasted money and severe dissatisfaction.

Original complete post below:
____________________

j bjork said:
Just stop with this bullshit, someone might think that you know what you are talking about
This is not bs, it is real and fact. Ask Elon Must about it about the battery charging and why the BMS is not needed. He is the guy who successfully designed (and engineered) his electric cars and how their batteries have shown to hold up. The technology we the general public have been taught to believe is not of truth. The problem is that the engineers who made these little BMSs/balance chargers for small applications like e-bikes

[mod edit].

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#### harrisonpatm

##### 1 kW
cheez said:
Ask Elon Must about it about the battery charging and why the BMS is not needed. He is the guy who successfully designed (and engineered) his electric cars and how their batteries have shown to hold up.

Hey, I just got off the phone with Elon Musk, and it turns out, Tesla actually does use a BMS, in both their cars and powerwalls.
https://tesla-info.com/guide/tesla-bms-calibration.php
https://circuitdigest.com/article/tesla-model-s-battery-system-an-engineers-perspective

#### JackFlorey

##### 100 kW
cheez said:
All Teslas have BMSes.
He is the guy who successfully designed (and engineered) his electric cars and how their batteries have shown to hold up.
Because they use BMSes.

#### JackFlorey

##### 100 kW
cheez said:
If you were to run a speed test by shooting a light from a flashlight (or laser beam) from one point to another, the electricity will will form much faster, connecting the two points side by side.
So electrons travel faster than light. Wow. You really do have no idea what you are talking about.

Here's a challenge for you. There is a 1 amp current in a 2mm diameter copper wire. What is the average (drift) velocity of the electrons in that wire?

#### nicobie

##### Moderator
Staff member
I have been busy editing the dangerous content out of cheez's posts and have also asked him politely to quit posting about technical matters. We'll see what happens...

If I've missed anything that would cause a person new to ebikes trouble, please send me a message or report the post and we will correct it.

Thank you,

Nick

#### cheez

##### 100 mW

Cheez posts consistently dangerously incorrect information and advice that could lead to fire and death (in regards to batteries, etc).

Other information is simply incorrect and could lead to wasted money and severe dissatisfaction.

Original complete post below:
____________________

Ok I read the contents in the links you guys have provided. They pretty much support what I have been saying this whole time that the batteries balance themselves and charge them individually in multiple packs, or modules in their terms. I am afraid you guys got Tesla's meaning of BMS wrong, thinking you would use BMS to balance charge each and every group of parallel grouped cells in the entire battery system in a car. The BMS they are explaining is that they are used for monitoring voltages (total voltage) per module, or pack (as each contains both series and parallel arrangement of the cells). 16 modules interconnected via copper busbars to enable a complete single large battery pack. Each modules can be measured in voltage as they are separated from each other as individual circuit. If you read carefully they said the batteries self-balance. The BMS in their terms (or intention) are there to measure the voltage, temperature, and control charging, to prevent overcharging or over-discharging. It doesn't say anything about they use BMS to "balance charge" every cells or every parallel grouped cells.. The other web link you posted also shows about the voltage monitoring and calibration. Because the battery charge level fluctuates due to weather and the driving of the vehicle it uses algorithm to predict how much of charge remaining in your vehicle while driving. You would have to stop the car to get more accurate reading of the 16 independent modules, to determine the actual state of the charge per bank, a module, or pack. The website also said you have to stop the car for the BMS to properly calibrate to provide you more accurate reading of the charge. I was right about interconnecting these packs via busbar... They are also mechanism to engage or disengage connection between these packs. Each pack is only 22.8V (for the Model S). That makes it very easy on the battery cells to be charged. The charging is spread to all 16 modules independently (16 circuits).

ebuilder said:
Cheez, drift velocity of electrons is slow and even an electric field generated via a battery potential is less than the speed of light due to the resistance of a conductor such as copper.
The resistance of the conductor builds up heat (loss of energy). Doesn't mean the electricity is "slowing" down. You can have different rate of energy due to the limitation of the conductivity, but it does not mean that the electricity is slowing down to Mach 46.9 or Mach 6 (figurative speech). It doesn't work that way. The electricity is formed instantly when the two points of battery terminals are connected in a circuit.

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#### Chalo

##### 100 TW
ebuilder said:
For example, some people, quite sure its in the ten's of thousands believe, its ok for a transexual girl athlete who was born a biological male with XY chromosome to compete against biological women...that its fair. T

#### 999zip999

##### 100 TW
Ok I will call Elon and talk it out.

#### eMark

##### 100 kW
FACT: No two cells (even if they have the same model number, manufacturer, production) have the same SoC, self-discharge rate, capacity, impedance, and temperature.
Depends on one's definition of same (to the 1st, 2nd, or 3rd decimal point :wink: ). Authentic TESLA 2170 cells probably come the closest to same as any, and yet a BMS is a must to keep TESLA cells the same for as long as possible :thumb:

Even with more and more cycle age variance an 'active' BMS is still able to keep all the parallel groups the same, even with a DIY build using salvaged cells (for the life of the battery :wink: )

Ebikers define same as parallel groups within 25-30mV using a 'passive' BMS . In order to maintain that tolerance the Charger needs to stay on for several hours after the GREEN light comes on ... say every month depending on condition of the cells.

#### JackFlorey

##### 100 kW
cheez said:
Ok I read the contents in the links you guys have provided. They pretty much support what I have been saying this whole time that the batteries balance themselves and charge them individually in multiple packs, or modules in their terms.
Then you didn't understand what you read.

The BMS in their terms (or intention) are there to measure the voltage, temperature, and control charging, to prevent overcharging or over-discharging.
Correct. And that disagrees with what you said above.

You would have to stop the car to get more accurate reading of the 16 independent modules, to determine the actual state of the charge per bank, a module, or pack.

Nope. There are more ways to measure capacity than measuring voltage.
The resistance of the conductor builds up heat (loss of energy). Doesn't mean the electricity is "slowing" down. You can have different rate of energy due to the limitation of the conductivity, but it does not mean that the electricity is slowing down to Mach 46.9 or Mach 6 (figurative speech).
So what is the average (drift) velocity of electrons in a 2mm diameter copper wire carrying 1 amp? Mach 47? Mach 6? Give us a number if you understand this so well.

#### JackFlorey

##### 100 kW
ebuilder said:
For example, some people, quite sure its in the ten's of thousands believe, its ok for a transexual girl athlete who was born a biological male with XY chromosome to compete against biological women...that its fair. This is two divergent groups of people who draw very different conclusions given the same data.
And some people are so stupid that they don't know that there are tens of thousands of women in the US who are XY, and have been since birth. And often even they don't know.

#### JackFlorey

##### 100 kW
ebuilder said:
To be clear Jack, you made the leap which is ok that a lot of people don't know about the above. Absolutely true.
The above was the result of frantic googling. Specifically, you copy/pasted this Quora post that you found:

https://www.quora.com/Can-a-woman-have-X-Y-Chromosomes

Good for you! You learned something.
But above is very different than a human born a male, competing against humans born female.
Nope. AIS women produce testosterone. Some of their cells are simply insensitive to it, which is why they develop as women. However, they are also often stronger than XX women due to the presence of that testosterone.
Perhaps you have more in depth thoughts you would like to share including a person's gender has nothing to do with their biology. That gender is a choice.
Sex is biological. Gender is societal. Pretty simple.

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