BMS necessary or not

[husknbusk]

I noticed this thread on Will's website. It says:

You can use a dedicated BMS for your LiFePO4 battery to manage various safety features, but you don't need one. You can build safety protection features as you please. Also understand that many BMS available online are cheaply made and will fail before the battery does. Many EV/marine forum people agree that a BMS is more of a liability than a benefit, unless you spend the big bucks. High quality BMS are so expensive that you are better off buying a drop-in lead acid replacement lifepo4, like the battle born, that has an actual warranty and will last for ages (click here to learn more). If you are trying to build a super cheap battery with good LiFePO4 cells, and you follow the instructions on this page and add the most basic safety features, you wont need a BMS.

But he seems to use BMS's in the videos I've seen. Is this logic still sound? I'm just getting started and wondering if there's consensus on which direction to go: with BMS or without. I'm going the DIY route anyway, so is it much bigger of a deal to balance the cells myself and choose a charge controller with temperature cutoffs instead of using a BMS?

 

[curiouscarbon]

absolutely recommend BMS

make sure the BMS can disconnect if low voltage low temperature etc.

please ask more questions as you see fit.

 

[snoobler]

Welcome to the forum.

BMS unless you have a damn good reason not to use one.

@Will Prowse tagged to bring that portion of the website to his attention.

 

[husknbusk]

Wow, thanks for the quick replies!

I noticed Will's teardown of the Ampere Time 12v LiFePo concluded its in-built BMS lacked low temperature cutoff. Is it a big deal to compensate for that using the charge controller?

I was looking at this Lisuateli--no reviews, but the info claims to have low temperature cutoff, and it's fairly inexpensive compared to BattleBorn and even the lower cost Ampere Time. If you have a gut instinct about taking the "risk" on it, I'd be happy to hear.

 

[John Frum]

Wow, thanks for the quick replies!

I noticed Will's teardown of the Ampere Time 12v LiFePo concluded its in-built BMS lacked low temperature cutoff. Is it a big deal to compensate for that using the charge controller?

I was looking at this Lisuateli--no reviews, but the info claims to have low temperature cutoff, and it's fairly inexpensive compared to BattleBorn and even the lower cost Ampere Time. If you have a gut instinct about taking the "risk" on it, I'd be happy to hear.

My gut and my brain both say wait and see.
If it gets 250 genuine reviews and the ratings are good then maybe.
Of course the price will probably increase if the product is fit for purpose.
Also I like to see some nit-picky bad reviews.
That suggests to me that somebody couldn't find much to fault.

 

[HRTKD]

I noticed this thread on Will's website. It says:


But he seems to use BMS's in the videos I've seen. Is this logic still sound? I'm just getting started and wondering if there's consensus on which direction to go: with BMS or without. I'm going the DIY route anyway, so is it much bigger of a deal to balance the cells myself and choose a charge controller with temperature cutoffs instead of using a BMS?

Many of us cringe when someone brings up that quote/video. I would never use LiFePO4 cells without a BMS.

 

[John Frum]

Many of the lithium chemistries "vent with fire" if the cells get outside of the safe envelope.
Lifepo4 is pretty safe by comparison but they do have vents(presumably for a reason) and the cell contents are toxic.
@Will Prowse has first hand experience with this.
I don't know what it takes to make one vent and I'm not keen to find out.

 

[Ampster]

I have been on the diyelectriccar forum for almost ten years and in the early days there was active debate about pros and cons of BMSs. Most of that debate was about the benefits of bottom balancing a DIY EV pack.

I would NOTsay today that, "many EV forum people agree that it is a liability". There were few choices back then. Since then many brands have been proven to be reliable and the ones that failed to be reliable have gone out of business.
The thing that really convinced me was that no EV manufacturers built EVs without BMSs.

 

[Will Prowse]

I noticed this thread on Will's website. It says:


But he seems to use BMS's in the videos I've seen. Is this logic still sound? I'm just getting started and wondering if there's consensus on which direction to go: with BMS or without. I'm going the DIY route anyway, so is it much bigger of a deal to balance the cells myself and choose a charge controller with temperature cutoffs instead of using a BMS?

Use a BMS. Read the red text.

We ran without BMS a few years back because we didn't have any good ones available, or they were $1000+. Use a BMS.

I am going to add more warnings to that page now.

 

[Will Prowse]

Wait, how did you find that page?? It is hidden from navigation. Would be interested what link brought you to that page. I have had it down for at least a year now.

That was actually a very informative page. If someone were to follow it 100%, they could easily run a pack without a bms. But considering the posts I see on this forum, I will never ever EVER recommend not using a BMS. ALWAYS use a BMS!!

 

[Will Prowse]

I don't know if I can be anymore clear with my viewers. This is the only video out of 250 videos that mentions not using a bms (I took down the whole other series of videos on this and how to do it properly), and it clearly states that you should use a bms:


I just watched the video as well, and it covers everything. BMS or not. I think I should leave the video up. What do you guys think?

 

[husknbusk]

I was doing Google search queries and it came up that way. I guess it was the "side door".

 

[Will Prowse]

I was doing Google search queries and it came up that way. I guess it was the "side door".

Wow, good to know! That page gets practically zero views. I will hide it from the search engines now. Thank you

 

[husknbusk]

Use a BMS. Read the red text.

We ran without BMS a few years back because we didn't have any good ones available, or they were $1000+. Use a BMS.

I am going to add more warnings to that page now.

Thanks--I noticed the red text after I'd already read through the page and I was all macho about not needing a BMS at that point because of that paragraph I quoted, lol. Cool how experience has changed prevailing wisdom.

 

[bocephus]

how about the other direction--with a good quality BMS, do you really need a solar charge controller??? My Victron SCC on my solar golf cart went out and I'm thinking that the high quality bluetooth BMS on the battery pack that I built would make a new Victron redundant... Please shoot holes!

 

[Supervstech]

how about the other direction--with a good quality BMS, do you really need a solar charge controller??? My Victron SCC on my solar golf cart went out and I'm thinking that the high quality bluetooth BMS on the battery pack that I built would make a new Victron redundant... Please shoot holes!

No, a BMS really only has two jobs, balancing imperfect cell voltages, and disconnecting if balance, or voltage gets too far, high, or low.

You CERTAINLY do not want to rely on the BMS to set battery voltage.

It is a safety, like a circuit breaker… it is not designed to maintain correct voltage safely.