What's The Best BMS? (Grrrr... ?)

[tictag]

How many times have we heard the question, "What's the best BMS for my situation?" on this forum and how many times have we responded, "Well, it depends..."? We then go on post-after-post, page-after-page talking about what BMS's are there to do, what BMS's are available, posting caveats and more-and-more links to more-and-more BMS products.

It is a question that nobody on this forum has a 'go to' answer for.

Is anybody willing to 'do the digging' on this? Identify all (most common) BMS solutions, compare and contrast feature sets, identify limitations and come up with 'suggested further investigation' on product x, y and z for scenario a, b and c?

Note: I very purposefully do not suggest we come up with a Top10 BMS's because the 'best' BMS might not be the 'best' for every scenario.

I have never purchased a BMS before in my life, have literally ZERO first-hand experience, so I don't think I'm the best candidate to take this on ... but I know some of you regulars have such experience and some of you have time to spare to help our forum members.

Any takers?

I am aware of the following BMS manufacturers / products:

• Daly BMS
• Ant BMS
• Chargery
• SBMS0
• TinyBMS
• Orion Jr
• Batrium

 

[Dzl]

I have been perturbed by the same issue for a while now, and agree with pretty much everything you have articulated here, and have been pondering what would improve the situation. I had been considering putting together some sort of index of the 5 or so most common BMS with a quick reference of features, current limits, etc, but never got past the half-baked idea phase (and I'm in the same boat as you, spend some time researching BMS' but no real experience).

Really there are two issues that need addressing.

1. People need help understanding what a BMS is and does
2. People need help choosing the best BMS for them
3. Actually, a third thing a lot of people are just seeking is confidence/reassurance/confirmation about a BMS they think might work for them

People really need help with the first question, but usually ask the second question. It seems almost everyday there is a new thread "what is the best BMS?" or "I bought 280Ah cells what BMS do I need?"

Its hard to answer the second question in a concise way regardless of the asker's knowledge, but its especially hard if they don't have a handle on what a BMS is conceptually. And I don't fault newbies for not understanding its a rather esoteric subject, with very few beginner friendly learning resources. Even most of us who have devoted some time to learning have pretty shaky understandings in my opinion.

I think two things would be very useful

1. A thread, wiki entry, or @Will Prowse video (or all of the above) that is an introduction to BMS', what they are, what features matter, how to size them.
2. A thread, wiki entry or @Will Prowse video comparing some of the most common BMS key features.

Honestly, I think this is perfect material for Will, there are a lot of people thirsty for this info, and he is quite good at explaining things in simple terms.

 

[Dzl]

Usually when I answer the question "what's the best bms" or one of its cousin questions, I frame it as a choice dictated by finding the option that best fits the asker's goals and needs and model.

And present options as a continuum from simple/basic/beginner friendly but less configurable/full featured (Daly) to somewhat more advanced, highly configurable and full featured but less 'plug and play' (SBMS0 among others).

The only other BMS I would add to your list is:

• DYKB / Overkill Solar / Battery Hookup BMS (JBD-SP04S020)
• Daly BMS
• Ant BMS
• Chargery
• SBMS0
• TinyBMS
• Orion Jr
• Batrium

 

[JoeHam]

I agree with everything said and would approach it from the other end, as in what features do you need. Obviously every use case is different and I use my BMS only to monitor and passively balance my cells. I also only balance during charging.

Here are some features/specs to determine before you go shopping what to look for:

What voltage?

What amperage? In my case zero amps since I don’t run my system through the BMS. Others may want high amp FETs or to run external relays.

Is low temp disconnect needed? For many this is a complete non issue if their cells live inside the home. For others it’s a deal breaker to save cells from certain destruction out in the wild.

What level of cell monitoring? Voltage only, internal resistance etc.

What level of charge control? I leave that up to my SCC but others want it in the BMS.

What amount of whiz bang wow features? Bluetooth, data logging etc to name a couple. Again, some couldn’t care less and for some it’s a deal breaker.

So I guess what I’m suggesting is a detailed feature list so people can decide what they want/need and then narrow their search greatly.

I spent a ton of time figuring out my need/want list. Getting the correct BMS was simple after that ground work was done.

I also propose spending an unlimited amount of Wills time to produce a video on this subject ? as no one does it better.

 

[tictag]

I also propose spending an unlimited amount of Wills time to produce a video on this subject ?

I feel sure that @Will Prowse would be eternally grateful for a 'community sourced to-do list' ... you know, to show him just how much we love and respect his support and guidance...

 

[danphillips]

I’ve been trying to decide on a BMS as well. To list some features that we need to consider when looking for a BMS.

Voltage is a given....

Cell balancing
active / passive (active-move power from cell to cell, passive-discharge power to heat)
start at a set voltage / always balancing
balance rate

Battery protection
battery low / high voltage cut off
cell low / high voltage cut off
protection switch type - fets or solenoid
Battery temperature ( edited in)

Battery monitoring
no monitoring - just let it do its thing
battery voltage
cell voltage
balancing activity
how viewed (Bluetooth, digital display, pc)


Settings
fixed & non-changeable
high / low - battery / cell disconnect
balance start / stop voltage / difference
some units have an extensive list of options and alarms

External connections
pc with custom software
downloadable data for charts etc
low / high power solenoids
warning buzzer / led

I welcome anyone to add to this list, maybe we can get some type consensus on the best options for a given usage. There seems to be a difference between full time daily users and mobile / occasional use installations.

 

[HRTKD]

JoeHam covered it but danphillips didn't: high/low temperature

Number of cells monitored: 4s, 8s, 16s, etc.

I don't know if it matters, or if it's possible, but if you use an 8s BMS on a setup with only four cells, will the BMS still work?

 

[Freep]

One thing I don't see here that, as a newbie, seems to always be missing is software for programming and monitoring the BMS. There are tons of videos about how to wire up a BMS but I have yet to see one about programming one or any kind of walkthrough of the programs that are being used. Is there a standard that most of them use or are all they all one offs?

As an IT veteran, it has taken me a long time to get in the habit of remembering that most people don't have the baseline knowledge I have. I think this is the same here. The veterans take for granted that everyone is going to have knowledge that they really shouldn't assume people have. I don't think this is a conscious assumption at all. I think a lot of people just forget how new a newbie is.

"Everything's new when you're new. The pope can be a Jew if you're new" -- The Gomers


Edit: I just thought of another example of my ignorance. I see all this talk about protection switches. Is this in the BMS itself or controlled by the BMS? I assumed the BMS just stopped charging or discharging when a boundary condition is met.

 

[danphillips]

@Freep, a BMS is a last chance protection device to protect your cells from under / over voltage. A balancing function keeps the cells in a equalized state. Some BMSs have internal fets which work like an electronic switch to disconnect your battery, while others use a solenoid as the switch.

 

[dmcdetroit]

I cannot tell you how relieved I am to read this thread. I posted a few days ago on the "how to choose a BMS" topic, which alluded to the issues that Tictag raised -- that is, what are the variables that I need to consider to make a BMS decision. I received one response from a staffer who answered my questions unambiguously and asked for information on the one variable I had not included. Thank you, Craig.

Like Tictag, I also am not interested in a Top 10 list, especially as they are usually presented without the critical context of variations in individual configurations. As others have noted, experience in other areas of electronics and mobile electronics can only translate to a certain point. For example, I am working with someone who is an Extra in ham with extensive experience with electrical components, batteries, and so forth -- just not in the context of homebrew LI-x, which is at the core of my system at least and the key safety component, I would imagine, for DIYs.

If someone were inclined to take this on, I am a professional technical writer and I would be happy to work with them on the best way to present the information so that it is useful both to more experienced solar users and newbies like myself.

 

[Sipma02]

Really there are two issues that need addressing.

1. People need help understanding what a BMS is and does
2. People need help choosing the best BMS for them
3. Actually, a third thing a lot of people are just seeking is confidence/reassurance/confirmation about a BMS they think might work for them

...

Honestly, I think this is perfect material for Will, there are a lot of people thirsty for this info, and he is quite good at explaining things in simple terms.

I also am relieved to read this thread. As a newcomer to this forum, I have done TONS of reading and searching, and I think I have a good handle on conceptually what a BMS is, how to pick one, what my needs are, etc. I want to learn. This is DIYsolarforum after all. I do think #3 is a good consideration, that is my biggest thing right now. I'm happy to make a BMS decision and backup that decision with reasoning and research, but at the end of the day, this is my first solar setup and I am worried about missing something that might be obvious to someone with more experience. So #3 stuck out to me.

Definitely agreed that Will should make a video and it should be sticked somewhere, along with a written, somewhat technical document that corroborates the video (to follow along for us visual/written learners)

 

[dmcdetroit]

Honestly, I think this is perfect material for Will, there are a lot of people thirsty for this info, and he is quite good at explaining things in simple terms.

I watched some of Will's content; it may be simple for people who know something, but his language was too sophisticated out of the gate for someone like me without experience.

What I would find most helpful, just off the top of my head, would start with a straightforward presentation of the role of the BMS in solar systems (e.g., why it is needed and when it is *not* needed), an outline of the system variables that impact the BMS decision (e.g., types of batteries, configuration, inverter size), and how these variables align with the most common BMS features and types, including scenarios in which a simple balancer would suffice.

If this were well done, it might encourage BMS vendors to provide more of this information on their end as part of their specs. This could only be good for the industry, imho.

 

[tictag]

Some BMSs have internal fets which work like an electronic switch to disconnect your battery, while others use a solenoid as the switch.

And some others don't disconnect the battery at all - you might just get a beep or a flashing LED at best! But as has been mentioned, that might well be fine for a given scenario (and probably quite cheap, ahem, value for money!).

So, c'mon on! Who's gonna grasp this particular thorn? Who's gonna accept this particular hospital pass? Who's gonna drink from this poison chalice? Who's gonna .... OK, enough of that!

I do actually think that the 'doing the digging' task is complimentary to 'doing a video' task; I'm sure Will would very much appreciate all the right info all in one place that he can then add his own personality to for the silver screen. Or not, I guess I shouldn't assume.

 

[Ampster]

I would be happy to add my experience with the Orion Jr. It was designed to work with hybrid and battery powered EVs so it has many features not needed in a stationary storage application. It does have temperature sensors.

I know very little about the other BMSs.

 

[ToddF]

How many times have we heard the question, "What's the best BMS for my situation?" on this forum and how many times have we responded, "Well, it depends..."? We then go on post-after-post, page-after-page talking about what BMS's are there to do, what BMS's are available, posting caveats and more-and-more links to more-and-more BMS products.

It is a question that nobody on this forum has a 'go to' answer for.

Is anybody willing to 'do the digging' on this? Identify all (most common) BMS solutions, compare and contrast feature sets, identify limitations and come up with 'suggested further investigation' on product x, y and z for scenario a, b and c?

Note: I very purposefully do not suggest we come up with a Top10 BMS's because the 'best' BMS might not be the 'best' for every scenario.

I have never purchased a BMS before in my life, have literally ZERO first-hand experience, so I don't think I'm the best candidate to take this on ... but I know some of you regulars have such experience and some of you have time to spare to help our forum members.

Any takers?

I am aware of the following BMS manufacturers / products:

• Daly BMS
• Ant BMS
• Chargery
• SBMS0
• TinyBMS
• Orion Jr
• Batrium

I got the Overkill solar BMS on Amazon.
Big appeal is it has temp sensor.

The install sheet that comes with it says RETURNABLE FOR ANY REASON. If you Don't like it he will take it back, even if you burn it out. Steve has support forum on Reddit and he responds quickly to emails to his personal account. This degree of unconditional support is well worth the few extra bucks to me.

This BMS installed and working on 12 V 380 AH LiFePO4 bank 8 new 190 AH Cells from AliExpress. Haven't touched parameters yet, working on getting my motley crew of solar panels all on line. Steve answered my question said factory Parameters OK to start with and he was right.

For hand holding benefit I recommend Overkill.

 

[Freep]

Here's an example of what I feared would happen. My cells and BMS arrived today and I have this BMS that I can wire up but I have no idea how to program the thing and there is no manual. It's maddening.



Heh. I just noticed "discharge currnet"

 

[KohalaJim]

This BMS caught my eye while digesting content here. Looks to be rather plug-and-play and straightforward:

123\SmartBMS gen3 - 123electric

123electric.eu

 

[Airtime]

How many times have we heard the question, "What's the best BMS for my situation?" on this forum and how many times have we responded, "Well, it depends..."? We then go on post-after-post, page-after-page talking about what BMS's are there to do, what BMS's are available, posting caveats and more-and-more links to more-and-more BMS products.

It is a question that nobody on this forum has a 'go to' answer for.

Really there are two issues that need addressing.

1. People need help understanding what a BMS is and does
2. People need help choosing the best BMS for them
3. Actually, a third thing a lot of people are just seeking is confidence/reassurance/confirmation about a BMS they think might work for them

People really need help with the first question, but usually ask the second question. It seems almost everyday there is a new thread "what is the best BMS?" or "I bought 280Ah cells what BMS do I need?"

I just went and searched around the forum, and you are so right! I went to Beginner's Corner, to Frequently Asked Questions and found some good stuff but not a "What is a BMS" topic! And I see this thread already turning into what @tictag described. This would be very good (for someone) to add.

I'm not volunteering, I've only used two BMSs and none of the commodity ones. I'd be willing to chime in on some topics where I have experience. But to whoever does this, I think it is a decision tree, and start simple. I think the answer to @Dzl's issue 1 is pretty simple. And there must be some decent tutorial already on the web that could be linked. But all BMSs do three things, in various ways:
1) Cell-level monitoring--Measure key parameters such as cell voltage and balance to understand the state of the battery and its cells
2) Protections--Keep the cell parameters within desired limits to preserve the health of the battery and for reasons of safety
3) Cell balancing--Keep the cells balanced for higher total battery capacity and longer life

And then on issue 2, I think there are a few key questions that start from user needs and can significantly narrow the choices before going into the weeds on features and design:
1) Application? I.e. stationary off-grid, 4 season RV, mission-critical marine?
2) Power requirements? In particular will you have an inverter for AC loads, and what size?
3) Budget? $10s commodity on Aliexpress or $100s higher end
4) DIY hobbyist? Or just want a functional plug and play system?

I do think that last question is one of the key ones. Some come here asking about BMSs because they are technical and want to tinker. Others just want a more cost effective option than buying Battleborns. Either is fine, but solution options will be different.

 

[Dzl]

One thing that I would put out there that I think is both accurate and conceptually helpful for understanding the role of a BMS:
A BMS is a system, a way of accomplishing a goal, not a thing. Often it is a thing, a discrete component, but it doesn't have to be and often isn't.

Because FET based BMS are cheap, and popular here, we (myself included) usually think of and talk about a BMS in these terms, as a single unit. But the SBMS0 and the Chargery to a lesser degree are examples of a hybrid BMS with centralized command but decentralized control, and the Batrium watchmon4 and I believe the 123SmartBMS are examples of decentralized BMS'

As I understand it, a Battery Management System is defined by what it accomplishes and what its role is, (cell level protection and management of the battery). While there isn't necessarily agreement on the exact set of features that make something a BMS, I think at a minimum a BMS does (1) cell level monitoring, (2) low voltage disconnect (LVD), (3) high voltage disconnect (HVD), (4)* cell balancing

*I'm not sure I think point (4) is an essential feature but since every BMS I'm aware of includes it, I'm including it as an essential feature.

Are there other features I haven't listed here that you think should be or are essential features that a BMS absolutely and fundamentally should have. over current protection, high and low temperature protection and/or warning, data logging, State of Charge, State of Health, cell voltage delta disconnect, bluetooth or wifi connectivity, ability to interact with other components, are all features that a BMS could or should have, but not sure any qualify as universal must have's in every context, for every BMS. What do you think?

Further, for 'FET based BMS'' (sometimes called commodity BMS' or inline BMS') I think overcurrent protection and high temperature protection are arguably essential features, but more to protect the BMS than the battery.

 

[Ampster]

Most of the more expensive non FET based BMSs, for example the Orion Jr., have external current monitoring and use externally controlled contactors for LVD and HVD. I am including cell level voltage disconnects in the above. As a result they are only limited by the size of the current shunt and contractor in terms of current that they can handle.