Looking for a good bms

[Carolina Jim]

Hi jim here i want to build a 12v 100ah 4s lithium ion battery. but need help picking a bms any help would be great. Thanks. Jim

 

[snoobler]

Welcome to the forum. How much current do you need?

 

[Mike Jordan]

I just ordered 100ah cells. I was just getting ready to make the same post. I'll tag on instead.

I'm looking at 45amps tops. On average considerably less. I thought I would look at the 60amp BMS range for plenty of head room. I would like some BT connectivity. But thats probably a wiz-bang want, and not a necessity for me

 

[snoobler]

Daly makes a 12V 60A BMS w/30A charging, but it has no monitoring features, and it can't be programmed. I paid about $22 on Amazon.

 

[Mike Jordan]

Daly makes a 2V 60A BMS w/30A charging, but it has no monitoring features, and it can't be programmed. I paid about $22 on Amazon.

Link? on Amazon the 60a I found are 3x that price.

I found an ebay link that was $45

 

[snoobler]

Hmmm... unfortunately, it shows as unavailable now.

Amazon.com

I paid $21.55 after tax.

 

[Bob B]

Do some research on the Overkill solar BMS .... Should have plenty of capacity for you and Bluetooth monitor and parameter changing capabilities.

 

[Mike Jordan]

Hmmm... unfortunately, it shows as unavailable now.

Amazon.com

I paid $21.55 after tax.

Dayum! you put them out of biz

 

[snoobler]

Dayum! you put them out of biz

Dude. I'm their bitch. I made the mistake of running those reports to see how much you spend at Amazon... It was completely and totally shameful. They got a lot of mah money!

 

[Dzl]

I just ordered 100ah cells.
I'm looking at 45amps tops. On average considerably less. I thought I would look at the 60amp BMS range for plenty of head room.

You are on the right track here (building in substantial safety margin). Often BMSes have different ratings for charge and discharge, so its worthwhile to have an idea what each will be.

As has been mentioned for smaller, simpler systems either the JBD Smart BMS (sold by Overkill Solar and others) or the Daly BMS are good options. The Daly is lacking BT, user configurable settings, and low temp cutoff but its a solid barebones BMS and pretty cheap. Overkill solar has BT, low temp disconnect, and good support and documentation. Its a good beginner friendly option.

 

[Carolina Jim]

Welcome to the forum. How much current do you need?

This will be my 1st battery build so im not shure how much i need ???

 

[Dzl]

This will be my 1st battery build so im not shure how much i need ???

This is the most important factor in determining BMS size/rating so its pretty important you get some idea what your max current draw will be.

This is the somewhat tedious but important step of thinking through and adding up all the loads (power consumers) that might run at one time.
An 'energy audit' will help answer this, and other important questions about your system.

Alternatively, you can just buy a BMS that is significantly larger than you think you might need, or can carry more current than your battery is rated for if you want to sidestep the energy audit. But you at least want to have an idea what your major consumers will draw.

You have a 100Ah battery, if its rated for 1C, you should never go above 100A continuous, and ideally you should try to stay below half that most of the time. If you buy a ~120-150A BMS you can be relatively sure it will not be the bottleneck

 

[Carolina Jim]

This is the most important factor in determining BMS size/rating so its pretty important you get some idea what your max current draw will be.

This is the somewhat tedious but important step of thinking through and adding up all the loads (power consumers) that might run at one time.
An 'energy audit' will help answer this, and other important questions about your system.

Alternatively, you can just buy a BMS that is significantly larger than you think you might need, or can carry more current than your battery is rated for if you want to sidestep the energy audit. But you at least want to have an idea what your major consumers will draw.

You have a 100Ah battery, if its rated for 1C, you should never go above 100A continuous, and ideally you should try to stay below half that most of the time. If you buy a ~120-150A BMS you can be relatively sure it will not be the bottleneck

Ok that's what i thought. my end goal will be 3 of these battreys. my needs at the cabin are small led lights water pump 12v fan and such. how do you know you are getting a good quality bms at a good price .amazon doesent have much that i have found. Thanks for helping me i know im lost with this stiff but love to learn but at 53 i don't retain much. Thanks. Jim

 

[Carolina Jim]

Hi jim here i want to build a 12v 100ah 4s lithium ion battery. but need help picking a bms any help would be great. Thanks. Jim

I have another question. can i buy a smart bms and use a 12s and connect to 3 separate 4s battery cells???? Thanks jim

 

[Dzl]

I have another question. can i buy a smart bms and use a 12s and connect to 3 separate 4s battery cells????

No. the __s refers to # of cells in series. 4S = 12V, 8S = 24V, 12S = 36V

If you will have 12 cells, and want a 12v system you have two options:

1. build 3 x 4S battery packs each with its own 4S BMS (this is called 4S3P or "series first"). Basically you build 3 separate independent batteries and put them in parallel
2. build 1 x 3p4S battery pack with a single 4S BMS (this is called 3P4S or "parallel first"). Basically before you put your cells in series, you create groups of 3 in parallel each group behaves as (and is seen by the BMS as) a single cells, then you put those 4 groups in series to create 1 x 12 cell 12 volt battery.

If you are buying/building one at a time, really your only option is the first option.

Ok that's what i thought. my end goal will be 3 of these battreys. my needs at the cabin are small led lights water pump 12v fan and such. how do you know you are getting a good quality bms at a good price

Its a fraught market, not quite as bad as the raw cell market, but competitive. Stick with what others have used and had good experiences with. Learn about the basic purpose and function of a BMS (there are a wide range of features, the core essential featureset is cell level monitoring, balancing, and high and low voltage disconnect, low temperature disconnect is also important).

The two 12V BMSes I recommend most to newbies are:

1. The JBD Smart BMS (specifically the one sold by Overkill Solar--which stands out due to the beginner friendly support, documentation, and good customer service/return policy). I think it costs around $120 for a 120A BMS
2. The Daly BMS, much more basic, but well tested and cheap. Zero configuration burden for the user, but also zero configuration ability. A 150A Daly BMS can be had for $85 or 100A for $35, higher current versions go all the way up to 500A but cost substantially more. Two things to be aware of with Daly, no low temp protection, and a choice between common and separate port.