Do I really need a bms?

[Range]

Do I really need a bms? If I can monitor my batteries manually? That is by ensuring I don't discharge below 12v and don't overcharge above 13.8v? Do a top voltage balance say once a month?

 

[MisterSandals]

Yes, Yes, No, No

Search results for query: do i need a bms

diysolarforum.com

 

[Bud Martin]

You become the BMS and you have to monitor each cell like hawk. There are many threads in this forum about 'Do I need BMS'.

 

[Range]

Thanks Bud

 

[time2roll]

Just keep in mind you need to monitor at the cell level.

 

[Range]

Just keep in mind you need to monitor at the cell level.

Yes each cell still at 3.461

 

[Thisguy80]

BMS haha (battery monitor system) do you need one?? I’ve used 4 sets of LFP banks for years without. Another automated system in your life to fill gaps in time or limited capabilities.
Real question is are you able to monitor yourself with understanding consequences of error in operating range that doesn’t aim to pull full capacity(red lining them)?
Range not to close to cliff either side all but eliminates chances of falling off.
And everyone uses some sort of indicators which it self is BMS that you play more important role.
Any system can malfunction so either way risks are present.
Seems the BMS is just replacing what you have to monitor closely instead of batteries.
People tend to move there attention to systems doing the automated steps instead of underlying process.
Will BMS make things easier? Sure if it’s good product and you know how to set it up and install correctly, putting all the weight on it to do it’s job at same time saying CC could malfunction.
Finding a good product now a days as proven difficult but possible so major part of if auto BMS will even lower risks of falling of cliff.
Not saying BMS don’t have a place but saying it’s not full prove plan as most seem to suggest.
I’m sure most have heard if you want something done right do it yourself.

 

[curiouscarbon]

yes, a hardware BMS that will disconnect the battery is quite essential.

if any cell voltage goes too high voltage or too low voltage the BMS will disconnect the battery and protect the cells from permanent damage.

JBD make pretty decent BMS, there are other brands also. MOSFET type use very very little power, Contactor/Relay type use a small amount of power when connected.

good luck!

 

[Thisguy80]

Oh yeah I’ve definitely heard. Think it’s the 11th commandment now. Even my mom knowS it’s absolutely necessary and she has only ever used disposable AA.
Even tho I’ve been running without on multi banks without for years now.
I do have a $3 alarm if any cell deviates or total voltage leaves my range.
I didn’t say it’s a bad idea just saying it’s called a battery monitor system which there others ways to accomplish this that doesn’t say BMS but still does same thing.
You could literally hire someone to monitor for you with couple basic tools.
Advantage of BMS(as it’s preached) is it limits your involvement while putting all the weight on one thing to control the show.
It’s always the goal to minimize labor cost, I’ve just always played more fundamental role of various projects I do to for deeper understanding that helps with future decisions.
But yes I’ll get in line and say BMS is absolutely necessary. Yes yes yes don’t think just do

 

[Samsonite801]

Do I really need a bms? If I can monitor my batteries manually? That is by ensuring I don't discharge below 12v and don't overcharge above 13.8v? Do a top voltage balance say once a month?

I guess it depends on how much you spent on your cells, and how much time you have on your hands to manually watch over them.

And if they are a cobalt-based chemistry which is at higher risk of going into thermal runaway, maybe you're a fireman too?

 

[Bob B]

now.
I do have a $3 alarm if any cell deviates or total voltage leaves my range.

Can you give us the detail of how you are doing that?

The cell level monitoring is the necessary function that pushes most everyone to a BMS .... Just curious how you are accomplishing that so inexpensively.

 

[houseofancients]

Oh yeah I’ve definitely heard. Think it’s the 11th commandment now. Even my mom knowS it’s absolutely necessary and she has only ever used disposable AA.
Even tho I’ve been running without on multi banks without for years now.
I do have a $3 alarm if any cell deviates or total voltage leaves my range.
I didn’t say it’s a bad idea just saying it’s called a battery monitor system which there others ways to accomplish this that doesn’t say BMS but still does same thing.
You could literally hire someone to monitor for you with couple basic tools.
Advantage of BMS(as it’s preached) is it limits your involvement while putting all the weight on one thing to control the show.
It’s always the goal to minimize labor cost, I’ve just always played more fundamental role of various projects I do to for deeper understanding that helps with future decisions.
But yes I’ll get in line and say BMS is absolutely necessary. Yes yes yes don’t think just do

oh for sure dont get inline, but do post the pictures when you stuff burns to the ground..

'come on dude all jokes aside ;

there a whole forum section dedicated to "crap i done stupid", but it's always your choice and responsibility, just dont get on a high horse when people give you advise/try to help you

 

[Samsonite801]

I guess it depends on how much you spent on your cells, and how much time you have on your hands to manually watch over them.

And if they are a cobalt-based chemistry which is at higher risk of going into thermal runaway, maybe you're a fireman too?

No, all kidding aside, the BMS does perform 5 tasks at minimum...

Low-temp cutoff
High-temp cutoff
Low-voltage cutoff
High-voltage cutoff
Cell balancing (cell-level voltage awareness)

Additionally, the bluetooth managed ones give a really simple way to read logging, see current status, troubleshoot, read cell voltages, make BMS configuration changes, etc.

 

[A.Justice]

I guess if you're going to be physically sitting in front of your cell monitor, every single time you charge and discharge your cells, at any rate, the ENTIRE time, then you could probably get by without a BMS.

However, if you intend to charge or discharge, and even step out of the room for coffee (there's multiple stories on here where people stepped out for a drink, and overcharged their cells while they were gone), then you should have a BMS monitoring your batteries for you.

I just don't understand why anybody wouldn't use one now, there are MANY great units available for under $100, which is normally less than the cost of a single cell. It might work, until it doesn't, and the consequences of an overcharged cell can be catastrophic.

 

[Samsonite801]

I guess if you're going to be physically sitting in front of your cell monitor, every single time you charge and discharge your cells, at any rate, the ENTIRE time, then you could probably get by without a BMS.

However, if you intend to charge or discharge, and even step out of the room for coffee (there's multiple stories on here where people stepped out for a drink, and overcharged their cells while they were gone), then you should have a BMS monitoring your batteries for you.

I just don't understand why anybody wouldn't use one now, there are MANY great units available for under $100, which is normally less than the cost of a single cell. It might work, until it doesn't, and the consequences of an overcharged cell can be catastrophic.

Yeah, and here's the thing, I've read about an older trend in the boater community (more in European countries), who would run without BMS, because they claimed they had their inverters and charge controllers set up to stop on critical limits.

And I know you can get a Victron (and perhaps other brands too) of charge controller setups with temperature sensors, etc, and set them to tight parameter and stop the current flow when they hit volt and temp limits.

However, a failure which those setups can't account for, is that since they only have a visibility into entire bank level voltage, if a single cell fails in a series string, and pulls the volts down on the entire bank, the charger will just try to charge on the bank even more, and overcharge all the good cells, taking out the entire bank.

BMS gives a cell-level voltage monitoring, so if a single cell goes outside voltage limits, it will stop current on the whole pack.

And yeah, the price of BMS is not super high, it is cheap insurance. I've even heard it can be wise to add a BMS onto non-lithium battery chemistries as well. I have seen several for sale on AliExpress and other places which state that certain models specified will support lead chemistries as well.

BMS is the last line of defense when all other measures on battery protection fail.

 

[ericfx1984]

Do I really need a bms? If I can monitor my batteries manually? That is by ensuring I don't discharge below 12v and don't overcharge above 13.8v? Do a top voltage balance say once a month?

well you can pay for a BMS... or pay for your personal value per hour

 

[timselectric]

Do you need it, no.
Should you have one?
Absolutely
For sure
Without a doubt
Of course
100%
And, yes.

 

[Thisguy80]

Like I said I didn’t say bad idea but..
The amount of people running no BMS vs ones with issues is very small percentage, can something go wrong of course and this is also true of BMS units being sold so when or if it fails don’t come crying to manufacture.
Level of safety and ways to minimize risks are always a factor.
I’m not attempting to change anyone’s mind as that’s nearly impossible.
BMS can fault and will not for everyone but a percentage as with other methods.
I guess what I’m saying is people are obsessed with automation and tend to focus on that process and it’s with everything, accounting for 50% of product advertising by word of month by consumer.
Does automatic processes make life easier sure, it’s not like I’d like to continue to tweak my carburetor car all the time for it to run correctly vs my fuel injection get in go car but I do understand how to make that happen which is just another method from getting from A-B
We use airbags etc but helmet could be better in car why since professional drivers sure do,along with full frame roll cages, wouldn’t that be safer? They seem to think so and numbers clearly show it,but we use a different process instead. Even tho deaths using that equipment is far safer and hard to argue.
I have no self interest either way and just thought a DIY crowd were more open to options outside of norm.
Bottom line I wouldn’t recommend my process, especially to people new to LFP chemistry.
While many utilizing this technology is driving money towards better product and more competitive market getting the rest including me fully on board with idea of BMS is only way to go.
I’m sure if I was having issues it would drive me to other monitoring options.
My system is away from house in temperature controlled environment with remote alarms that if I had neighbors would wake them up and operate in window far away from edge it will be difficult to fall off.
It’s not really time consuming but I do check systems during the day probably more than some.
Going by internet and my experience with operating cells most push them to rated numbers so one guy results of battery life/issues could be totally different from another, just to many variables to account for.
One of the great features of internet is looking at people who come up with different ideas on how to do something, seeing or hearing of results that DIY crowd has done to fix or solve problems.
Long live the BMS as I’m sure I’m just late to the party.
You all win I surrender so no more rambling from me or car analogies. Closed.

 

[A.Justice]

Like I said I didn’t say bad idea but..
The amount of people running no BMS vs ones with issues is very small percentage, can something go wrong of course and this is also true of BMS units being sold so when or if it fails don’t come crying to manufacture.
Level of safety and ways to minimize risks are always a factor.
I’m not attempting to change anyone’s mind as that’s nearly impossible.
BMS can fault and will not for everyone but a percentage as with other methods.
I guess what I’m saying is people are obsessed with automation and tend to focus on that process and it’s with everything, accounting for 50% of product advertising by word of month by consumer.
Does automatic processes make life easier sure, it’s not like I’d like to continue to tweak my carburetor car all the time for it to run correctly vs my fuel injection get in go car but I do understand how to make that happen which is just another method from getting from A-B
We use airbags etc but helmet could be better in car why since professional drivers sure do,along with full frame roll cages, wouldn’t that be safer? They seem to think so and numbers clearly show it,but we use a different process instead. Even tho deaths using that equipment is far safer and hard to argue.
I have no self interest either way and just thought a DIY crowd were more open to options outside of norm.

The DIY crowd generally isn't interested in having their entire project ruined, or potential house / RV fire. I find it odd that somebody would use super high-tech modern lithium batteries, and not be willing to use the same high-tech monitoring systems that they require. To use a car analogy, this is like buying a 2022 Corvette, and saying that you don't trust the computer, so you put a carburetor back on it.

Bottom line I wouldn’t recommend my process, especially to people new to LFP chemistry.
While many utilizing this technology is driving money towards better product and more competitive market getting the rest including me fully on board with idea of BMS is only way to go.
I’m sure if I was having issues it would drive me to other monitoring options.
My system is away from house in temperature controlled environment with remote alarms that if I had neighbors would wake them up and operate in window far away from edge it will be difficult to fall off.
It’s not really time consuming but I do check systems during the day probably more than some.
Going by internet and my experience with operating cells most push them to rated numbers so one guy results of battery life/issues could be totally different from another, just to many variables to account for.
One of the great features of internet is looking at people who come up with different ideas on how to do something, seeing or hearing of results that DIY crowd has done to fix or solve problems.
Long live the BMS as I’m sure I’m just late to the party.
You all win I surrender so no more rambling from me or car analogies. Closed.

Just out of curiosity, how would your system handle a failing, low voltage cell if you weren't right on top of it? ALL cells WILL eventually fail, 100% of the time, it's just a matter of when it happens.

One cell starts to dip voltage, your pack appears to have a lower voltage than it "should" be, and now your charger is trying to put 14.4 volts on a 3S pack, which overcharges the remaining cells to 4.8v each. Now instead of a battery, you have a balloon (and hopefully not worse), all in the name of saving a fraction of a percentage of the total battery cost.

I just can't see a single reason to justify not having a BMS. I understand that you feel your situation is unique, and it very well may be, but I wouldn't suggest that ANYBODY try and build an unmonitored lithium pack.

 

[Samsonite801]

Just out of curiosity, how would your system handle a failing, low voltage cell if you weren't right on top of it? ALL cells WILL eventually fail, 100% of the time, it's just a matter of when it happens.

One cell starts to dip voltage, your pack appears to have a lower voltage than it "should" be, and now your charger is trying to put 14.4 volts on a 3S pack, which overcharges the remaining cells to 4.8v each. Now instead of a battery, you have a balloon (and hopefully not worse), all in the name of saving a fraction of a percentage of the total battery cost.

I just can't see a single reason to justify not having a BMS. I understand that you feel your situation is unique, and it very well may be, but I wouldn't suggest that ANYBODY try and build an unmonitored lithium pack.

Yeah, and to add to this a little. The reason this wasn't concerning to have a cell failure on a lead acid pack, is those cells are more tolerant to overcharging, as we would just see like the equivalent of an equalize charge voltage which might make it gas more, but wouldn't kill the cell.

Lithium cells are not as tolerant about overcharging without damage. And, if it is one of the battery chemistries involving cobalt (higher probability of thermal runaway), overcharging is one of the factors that can trigger a thermal runaway.

That's probably the main reason BMSs became the norm starting with cobalt chemistries was for safety purposes. Imagine if your cellphone battery didn't have a BMS, there would be more meltdowns in society like the Samsung Note 7 banning they had by the airlines...