Have You Built Battery Pack WITHOUT BMS?

[cheez]

Moderator advice to all readers:

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.

Do not follow any of their advice or information.


Original complete post below:
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Hi guys,

I have been wanting to buy batteries (Li-ion 21700 cells) and build the pack myself without the BMS and no soldering. Been wanting to do it nearly a year ago but never got the money to do it. For those brave ones out there that wanted to find new discoveries ,beyond the boundaries of man-created science, have tried to build battery pack without the BMS? What was your result? Did it work out OK for you? What were your experiences? I mean for e-bikes and e-scooters.

The reason why I bring this up is because BMS does many bad things to humanity. Here is the list:

- People (newbies) get discouraged and give up after watching the videos of highly complicated wiring and soldering on building DIY battery pack.
- BMS adds more potential problems due to its premature failure.
- BMS limits power (flow of current efficiency and effectiveness) and build heat when dealing with a lot of amperage from the battery discharge.
- BMS doesn't really work charging the battery cells safely.

Soldering is a whole 'nother problem..

 

[scianiac]

I currently don't have a BMS on my battery but I also charge it with a balancing charger, monitor it carefully and understand how to handle it safely. Honestly if your reason is that it's complicated to inexperienced builders and you have to solder then that is a very good reason why you want a BMS, if you don't understand how to install a BMS then there is zero chance you understand handling batteries in a safe manner without one. Potential problems caused by a BMS breaking are far far less serious than those caused by a battery damaged by not having a BMS. There are BMSs built to handle high currents and even those that are charge only and linked to the ESC so no additional resistance. One of the primary purposes of the BMS is to charge the cells safely, of course some are much better at this than others.

 

[transposon]

You can skip the BMS and use just an active balancer. If you do that, you really need a way to monitor voltage in real time (like a handlebar display) so that you know that you never dip below a safe voltage for the pack as a whole.

I have used this setup for over a year now without issue.

 

[DogDipstick]

"The reliability of any electronic device depends on how well the hardware protection circuits have been designed. The end user (consumer) is prone to make mistakes and it is the responsibility of a good hardware designer to protect his hardware from any mishappening. There are ample types of protection circuits each with its own specific applications."

Yup.

That is all I'm saying for right now.

 

[Diggs]

BMSs are so easily available and provide such a vital function I'm not sure why you would run without one? If you have a balancing charger for the high disconnect/leveling and a controller for the low disconnect and amperage control then I suppose a BMS is optional but why? They only cost a few bucks and offer some really important safeguards.

 

[john61ct]

BMSs are so easily available and provide such a vital function I'm not sure why you would run without one?

Just assuming any BMS will take care of your pack without ongiing testing & monitoring anyway is very risky

They often fail, and then destroy the cells, so you need to make them easily replaceable and keep the cells isolated from them when not in use.

You can instead implement the various functions more reliably with other circuitry.

 

[Diggs]

They often fail, and then destroy the cells, so you need to make them easily replaceable and keep the cells isolated from them when not in use.

Considering the millions or is it 100s of millions of BMSs out there working every day I think it's better to say they rarely fail. Yes, they do fail but it is rare. Your chance of a pack failure goes up exponentially without one.

 

[cheez]

Moderator advice to all readers:

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.

Do not follow any of their advice or information.


Original complete post below:
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Guys, those little tiny BMS wires soldered on the end of each columns of the battery pack don't really charge. The battery will not take the charge because the electrons are not directional. They don't flow from positive to negative, nor from negative to positive. The electricity appear instantaneously when the battery cells are connected via conductors (metals). The battery pack will only take the charge if the charger is connected to only the positive and negative ends of the battery pack. You have been charging the battery that way with the BMS or not.

You don't need battery balancing circuitry either. Because the electricity is not directional all the battery cells get the charge at the same time. Since not all battery cells are perfect (even with the same brand and model) each cell will take what it "can" take. You don't need the electronics to intervene how to charge these cells therefore. One cell will operate fine at 3.9V, the other at 4.2V, the other at 3.8V. If any of the battery cells dies due to a defect the other working cells will continue to do there job. The battery charger for the 60V is programmed to stop charging when the battery pack reaches 67.2V. Just make sure that you have enough battery cells to cover beyond 67V, giving you enough headroom. And you can't monitor the voltage of battery cell individually because all the cells are connected to act as a one giant battery cell.

 

[john61ct]

Without getting into back and forth, no confrontation, but any noobs reading this thread, please disregard the above post.

 

[999zip999]

I run 3 packs without BMS. One with BT BMS. The 3 just have balance wires for checking and to balance charge with thru the sense wire rc style charger. I might have damaged one 8 yr old pack by over discharge after 1,480 cycles . Can be old age ? Was 24s now 20s.
I do like BT bms aa I don't need balance wires 20s Samsung 30amp cells at 6p.
Cells are not self balancing, just good quality Cells down go out of balance as easily.
I use to believe you need a 15ah pack or bigger. But have a 20s spaim08 pack and I.can use it . This is after 14yrs and over 40,000 miles countless battery cycles. You learn things by the set of your pants and time.
BMS is a must have for 95% of people.

 

[eMark]

- BMS adds more potential problems due to its premature failure. (false generalization)
- BMS limits power (flow of current efficiency and effectiveness) and build heat when dealing with a lot of amperage from the battery discharge. (false generalization)
- BMS doesn't really work charging the battery cells safely. (false generalization)

I don't use a BMS, but NOT because of the above misinformation (insert is my doing). If what you believe is true then BMSs would be viewed as a scam and there would not exist a helpful 'smart' BMS (only as smart as its smart owner).

Your above 3 statements are based on a small percentage of BMSs ... primarily those cheapy Chinese BMSs, and DIY builds by noobs quick to fault the BMS when it's just as likely that the builder messed up. Your 3 above statements come across believing that the function of a BMS is to shorten the life of a Li-ion battery. You couldn't be more wrong.

Those that don't incorporate a BMS into their DIY build is because they have the know-how and supportive equipment that is better than even a good BMS. On the other hand a quality BMS is a necessity for those that don't have the know-how and supportive equipment and accessories. A quality BMS is used by many DIY builders that are smart enuf to know the benefit of incorporating a so-called quality 'smart' BMS as a useful addition to their DIY battery build.

 

[CONSIDERABLE SHOUTING]

I'm gonna add onto eMark's great post, especially that since I've been here a few years I haven't seen or heard of a BMS failure in years. Some finally did after 4-5 years of consistent use, but frankly that's even in the wheelhouse of consumer computer parts. Most the horror stories I heard were from 2012.

The reason why I bring this up is because BMS does many bad things to humanity.

If they're so bad, then why does every OEM manufacturer use a pack-level BMS?

- People (newbies) get discouraged and give up after watching the videos of highly complicated wiring and soldering on building DIY battery pack.

I'm a newbie and I'm not daunted by that. I'm more freaked by information paralysis, of having too many choices.

- BMS adds more potential problems due to its premature failure.

To you. But every manufacturer of eBikes up to cars and even massive grid-tie packs use BMS'es.

- BMS limits power (flow of current efficiency and effectiveness) and build heat when dealing with a lot of amperage from the battery discharge.

So do long wires. It needs to be accounted for like anything else.

- BMS doesn't really work charging the battery cells safely.

Soldering is a whole 'nother problem..

You don't use the BMS to charge your battery. It's role is a gatekeeper; it activates to trim charge off cells and bring them into consistency once they hit an individual set limit, and to keep the battery from discharging more than it physically can. It's role is when you as a person, can openly say "I am not willing to individually balance and check cells frequently" which is literally 99% of the population. To do that requires a charger that is capable, the same complicated wiring, and the ability to test individual cells and remove underpreformers with a multimeter- serious stuff.

The users here that don't use them do so because they KNOW how far they can discharge their packs, KNOW how to individually balance them properly, and KNOW how to remove poor cells. All of those people- Dogdipstick, Chalo (to an extent, he uses an active balancer) and Dogman Dan all have a massive amount of knowledge a newbie like myself doesn't. Telling new eBikers to not use a BMS is frankly, setting them up to either destroy their first battery accidentally and waste money at best, start a lithium fire at worst.

So as John said...

Without getting into back and forth, no confrontation, but any noobs reading this thread, please disregard the above post.

This whole thread is... not good lmao

 

[amberwolf]

You don't need the electronics to intervene how to charge these cells therefore. One cell will operate fine at 3.9V, the other at 4.2V, the other at 3.8V. If any of the battery cells dies due to a defect the other working cells will continue to do there job. The battery charger for the 60V is programmed to stop charging when the battery pack reaches 67.2V. Just make sure that you have enough battery cells to cover beyond 67V, giving you enough headroom.

Aside from whatever you mean by the last sentence, this is a great way to have a battery fire.

Without something (you and a multimeter and a resistor, etc; a BMS, whatever) to monitor during charging to ensure no cell charges beyond it's limitations, cells that are not all balanced, and thus distributing the total full charge voltage among them equally, will then have some cells that overcharge (severely if the imbalance is great), and that damages them. Enough damage in the right way and there will be a fire.

Similarly, during unmonitored discharge, the cells that are low in voltage may drop below a safe level, and if the imbalance is severe can actually be driven negative, and again, damage that can cause a fire can be incurred in them.

It won't matter that the charger stops at the pack's "full" voltage, or that the controller has an LVC that stops discharge at some point, because the voltages of the cells are not equal unless there is a process and mechanism in place (manual or automatic) to ensure that they stay that way.


If every battery pack was new, and made of perfectly-equally-capable cells, and used well within it's capabilities, and all cells started out equally charged, then the cells would stay this way and there would be no failures like the above.

But batteries age, and cells age differently because no manufacturing process is perfect, and no sorting process can tell how a cell will behave once it ages enough and microscopic defects begin to expand and affect cell capabilities, so they will begin to unbalance at some point, and that will only get worse with no mechanism or process to correct it.

And many batteries, including most ebike / scooter / etc batteries, and virtually all DIY batteries, are not made of even well-matched cells, much less perfectly-equally-capable ones. So they will easily unbalance without that mechanism or process.

The worst batteries, probably virtually all the cheap ones, are made of at best completley unmatched cells (which may or may not all even be the same brand and model), and at worst recycled garbage cells of completely unknown condition and capabilities, and will rapidly become badly unbalanced, often during every usage and every charge cycle.


So while you can do whatever you like for yourself, I don't think you should casually recommend that no one ever use a BMS, especially in the manner you have. You're likely to cause people that don't understand how things work to end up burning down their house, apartment building, etc., and cause loss of life as well.



It's certainly possible to run the right kind of pack without one, but generally it will require at least occasional user-monitoring and intervention to prevent unbalancing and potential damage.

There are certain use-cases where even skipping this may not be a problem for a long time (possibly years), such as with high-capacity well-matched EV-grade cells that are used well-below their current-delivery capabilities, in a mild environment, and not fully charged or discharged, so there is little risk of imbalance occuring and growing at least while the cells remain well-matched.

I've run such a pack (several, actually) for some years, but problems do eventually occur with them, and I have had to replace cells because of imbalance problems, which I only catch because of periodic manual monitoring at the cell level. If I did not do this, eventually the problem cells would either overcharge or overdischarge to the point they could become dangerous fire risks.

The average person, even if capable of doing this monitoring, etc., is not likely to be willing to do so on a regular enough basis to keep themselves (and everyone around them) safe.

Unfortunately, there are poorly designed, and poorly manufactured, BMS units out there, more than a few, and they can certainly cause the same kinds of problems they are supposed to prevent, including battery fires for any of the above reasons.

Even more unfortunately, the cheaper the battery is, and thus the more likely the cells are to have problems the BMS could monitor and prevent, the more likely the BMS itself is to be one of those crappy ones. And the more likley to have manufacturing problems with the interconnects both within and between the parallel groups of small-capacity cells, which exacerbates all the other problems.

But the majority of the BMSs out there don't cause such problems, and do keep the batteries in a safer condition than they would be without them.

So a better solution than not using a BMS is to not use crappy cheap battery packs with crappy cheap BMSs. And not use crappy cheap recycled cells, or cells with an unknown provenance, so that they are less likely to have the problems listed above, and use a process (manual or automatic, depending on the end-user's abilities and willpower) to monitor for and prevent problems.

An even better solution is to only use new, well-matched EV-grade cells that are high enough capacity to only require 1P, but this is expensive, often not all that power-dense and/or energy-dense, and usually means a rectangular / boxy battery format, which doesn't fit well in many applications. So it is unlikely to be a useful solution for the majority of applications and users out there.

 

[kudos]

Cheez, I ran my bikes on LiPo for years without a BMS.

IMHO you don't need a BMS with LiPo, the act of charging them balances them out.

I used to check the balance of my LiPo every few months and they would be so close I didn't need to balance charge, but I would anyway just in case it helped in the long run.

Then I built my first pack with 21700, I asked some of the same questions you asked and was advised to go with a BMS.

I did not add a BMS as I wanted to learn for myself why it would be required when I'd never used one before with LiPo.

After my first run I was shocked to see how far apart the cell voltages were. There's no way I would run a battery like that.

I immediately bought an ANT BlueTooth BMS and wired up the pack, it's really not that hard.

The pack is now balanced down to a 100th of a volt.

I would now never run a cylindrical cell battery without a BMS.

YMMV

 

[john61ct]

Part of the problem is, the term BMS can refer to wildly different things IRL

much like the term "Love" is inherently inaccurate.

Assuming all is well with fully automated systems is foolhardy, with a bank worth thousands, multiple redundant failsafe layers of protection are well justified.

Really, "a BMS" is just a given set of **functionalities**:

PER CELL / group voltage monitoring

Failsafe LVC and HVC protection backup for when other infrastructure fails

These two I consider worth using a BMS for, but ALL can be implemented otherwise.

But the QUALITY reliability, longevity cannot be assumed, regular testing is required

And build your battery so the BMS can easily be replaced / removed

ideally, do not leave it attached to the cells when the pack is not being cycled, unless you KNOW it will not drain the pack down too low.

rare:

High and / or low temperature cutoff

rarely implemented well:

Over-current

Balancing

 

[m3vuv]

I have building lion packs for about the last 6 yrs,mostly as i was chief tech for a company who imported e bikes so had a free source of warranty batterys reterns( mostly samsung 18650 22f cells),i started out building packs using the cells from the returned pack as they were free,i killed hundreds of cells by not using a bms,and so far had 3 nasty pack fires! scarey shit!!,now with hindsite i would never even think of building a pack without a bms,not only for the fact i have to now buy cells,but not using a bms is a sure fired way to burn your house down or ruin good cells,i now always use a bt smart bms,save yourself grief folks and learn by my costly fuckups by not using a bms,in short dont even use a pack without a bms unless its for display purposes only!.,hope this post saves folks making the same mistake as i did for years,i killed over 300 cells! and had 3 serious fires that needed the emergency services to attend,since using a bt smart bms no probs,cheers m3vuv.

 

[Chalo]

Ok guys,

Some more critical info I got from someone one who knows the truth about the battery charging.
And that the batteries exploding or catching fire is disinformation being spread all over the net.

He says that:
1). The batteries (as far as Li-ion is concerned) don't get damaged nor cause premature wear from overcharging, passing the 4.20V mark.

Fail. You can disregard anything that person has to say about batteries now.

https://lmgtfy.app/?q=overcharge+lithium+battery

Pretty much everything in your post above is in error.

I have personally witnessed a battery fire at the pedicab shop. It was started by charging an unbalanced battery. Pretty much the only time lithium batteries burn is when they're charging or when they have been physically damaged.

Therefore, charging a NiCd battery pack without the BMS would be fine. Some cells reach full charge sooner than the other cells stay charging without any stress, until the rest of the cells get fully charged. You don't need to worry about imbalance of the charging on the nickel cadmium battery cells.

I changed your statement above to make it true.

 

[nicobie]

It's rare a post has to be deleted because of dangerous info. This is one of those times. cheez apparently doesn't understand the limits of Lithium batteries. Please disregard anything about batteries that he posts.

 

[tomjasz]

It's rare a post has to be deleted because of dangerous info. This is one of those times. cheez apparently doesn't understand the limits of Lithium batteries. Please disregard anything about batteries that he posts.

Reminds me of…

Another Darwin award candidate.

 

[Kimchi]

I been using ES resources to help me build a better battery. This is my experience with my pack without bms.
Start with the type of battery, modem backup battery. Output will be week for motor application.
Bike, over volting front hub motor from 42v to 68v, climbing a 6% grade hill, 1/3 of a 17 miles trip. Full throttling most of the trip.
Battery is 14s7p, but due to lack of 14s balance charger, first build was two 7s7p packs. They are strung together with 24 AWG copper wire with preexisting tabs on batteries. I later got a tabwelder. Cells would not discharge evenly due to bad wire configurations which leads to heat build up, melting plastic wire cover, and burt off cooper wires. Would had to triple layers the 24 AWG on some sections. I want to avoid over building my pack. I want my copper wire to act as fuse wire if something goes wrong.
I package wrap my battery with clear tape so I can see what will need to be fix.
Some cells had over discharge causing the battery to reverse polarity. I know the pack can handle the trip, majority of the cell were 3.4v at the end of the rides. Had to rebuild part of the battery, but this time rewire to a true 14s7p pack.
Reconfigure my 12s balancer and 2s balance charger around the battery. I later put together a dedicated 14s balance charger with a balancer, solar lithium charger and 48 v power supply.
The end result so far. Battery balance charged to 4.16v end of ride most cell are around 3.6v. Had done many rides. I had not used bms before ,but if I add a bms on my current pack it would be an efficient pack verses building my first pack with bms. Sacrificed few cells on the way, but the goal was to build the best battery I can.

 

[amberwolf]

I want to avoid over building my pack. I want my copper wire to act as fuse wire if something goes wrong.

You might want to read this thread:
https://endless-sphere.com/forums/viewtopic.php?f=14&t=88039
And there are others about cell-level fusing I would also recommend; this list includes some of them:
https://endless-sphere.com/forums/search.php?st=0&sk=t&sd=d&sr=topics&keywords=fuse%2A&sf=titleonly

Some cells had over discharge causing the battery to reverse polarity.

I would recommend replacing any cell groups that did that.

If the entire battery did this, then I would replace all the cells.

Damage to cells can create a fire risk, and it's a lot safer to replace things than risk a fire (which could happen at any time, not just during discharge or charge, though those are more likely times).

 

[999zip999]

BMS who needs a BMS I put my battery in a pyramid with a ball of mercury hanging from the center it's very important that you polarize your pyramid before hanging the Mercury ball and before entering the battery it will charge it perfectly each and every time. Do put on balance wires for monitoring what they cellll checker. E.Z. No Cheezey. So E.Z.

 

[Kimchi]

I want to avoid over building my pack. I want my copper wire to act as fuse wire if something goes wrong.

You might want to read this thread:
https://endless-sphere.com/forums/viewtopic.php?f=14&t=88039

Let me clarify what I was thinking. For someone who unfortunately experienced by accidently shorted part of the battery during the built. My 24 AWG wire would just break quickly vs a thicker wire or nickel strip might be still heating up during the short.

Some cells had over discharge causing the battery to reverse polarity.

I would recommend replacing any cell groups that did that.

If the entire battery did this, then I would replace all the cells.

Damage to cells can create a fire risk, and it's a lot safer to replace things than risk a fire (which could happen at any time, not just during discharge or charge, though those are more likely times).

I agree..
That is why I would let my battery cool down before charging it. My battery monitor/balancer would show if any cells are lower than usual. If any cells are bad to the point of reverse polarity, cells and balancer would heat up very quickly during charge. Therefore I always check the temperature of the battery with my hand during the beginning of any charge. I do replace the bad cells. The bad cells will prevent my pack to be charged up.

a pyramid with a ball of mercury hanging from the center......
Do put on balance wires for monitoring what they cellll checker

Mercury? My guess is, you might think my pack is solder together. Due to the poor quality of the pic. (Tried to comply with the rule to keep file small size) Pack is 99% spot welded together. Only the old balance leads are soldered.
As for monitoring the cell, it's only done during charging. I rebuilt it enough that I have confident as how it will behave during usage and can roughly gauge the state of charge by the speed of the bike.

View attachment 1

 

[amberwolf]

Let me clarify what I was thinking. For someone who unfortunately experienced by accidently shorted part of the battery during the built. My 24 AWG wire would just break quickly vs a thicker wire or nickel strip might be still heating up during the short.

Just a thought:

You're accepting worse performance all the time (power loss as heat in the smaller wire) for the sake of a preventing potential problem during building the battery?

That's why I suggest those cell-level-fuse discussions as a start, so you can find a solution that may not impact performance as much while still providing for safety in such events.


FWIW, it sounds like you need to individually test each of your cells, based at least on the original cell manufacturer data, to eliminate any that are already damaged, and characterize the rest to eliminate any that can't handle the loads you're putting on them (or replace them all with cells that can handle it, if these aren't designed to).

That is why I would let my battery cool down before charging it. My battery monitor/balancer would show if any cells are lower than usual. If any cells are bad to the point of reverse polarity, cells and balancer would heat up very quickly during charge. Therefore I always check the temperature of the battery with my hand during the beginning of any charge. I do replace the bad cells. The bad cells will prevent my pack to be charged up.

If you have cells low enough to become reversed, your pack already has serious enough problems to require replacement of those cells (groups), even before they reverse.

Note that if you reverse a cell, you're now drawing current thru a damaged cell, causing more damage. The damage could cause a fire right then and there, while you're riding. Or it could cause one later, just sitting there when you are not around. Not just while charging it while you're there.

Also the heating indicating a fire-level event starting inside the cell may not happen at the beginning of a charge--it could happen at any time.

I still recommend replacing all cell groups that have ever experienced any such events.

Same for cell groups that have dropped and stayed below the cell specification for lowest allowable voltage when the load was removed. (usually about 2.8v).



Otherwise, you are risking fire, at any time, under any conditions.

The risk may be small, but the consequences are very high, including death, and destruction of buildings, etc.

If you live completely alone away from all other structures, and never bring this pack near other people or structures than your own, then you are the only one affected by this risk, and it's entirely your choice.

If anyone else could be affected by it, then that is something you should consider.

 

[john61ct]

Cells should be proactively replaced at a standard measured State of Health percentage

LONG before and perceptible symptoms of EoL emerge.

Industry standard for mission critical use cases is 80%

but otherwise consumers can probably stretch things out safely to 70% or even 60% but after that, fire risk with li-ion (not LTO or LFP) starts to climb exponentially.

Risking polarity reversal is just foolhardy.

As ignorant fools burn down more and more homes the authorities will start getting draconian, harming everyone in this community.