Need help deciding what BMS to go with

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Neb_sakard

New member
Joined
Nov 26, 2021
Messages
1
Hi,
Let me describe my project and I need help deciding what BMS to go with. I am planning on making a Powerwall to power some external devices. The inverter I chose would be a MPP LV2424.
Batteries would be 18650s and I am planning on wiring them to that I would have blocks of 55 in parallel and then run 7 of those in series. This would give me enough voltage to run the 24v inverter. As of now we would be only pulling 1100 watts but would like to build the Powerwall to be able to take the full load of the 2400watts. What BMS would be good for a project like this?
Thanks for all the help in advance
 

OffGridInTheCity

Active member
Joined
Dec 15, 2018
Messages
1,863
2400w/24v = 100a. Suggest a 125a or 150a 7s BMS. This is pretty mainstream and something like a DALY should work for you. This is just one suggestion - there are many in this 'lane' to choose from :)
 

cak

Member
Joined
Mar 14, 2021
Messages
97
I am currently operating a similar system but with many more cells in parallel(I think 150ish). The current pack is an old design and not the best cells but it has been meeting my needs for a 3000w Reliable(that is the brand it isn't actually reliable) inverter. The only thing I have noticed is under high load the voltage drop is significant so if the resting voltage is under 25 it will often hit the inverters low voltage shutoff. I am planning an upgrade to better designed packs of more selectively chosen cells(7s200p) soon but have to finish setting everything up. Eventually I have a bigger 6kw inverter but I figure that will need more batteries to work well, going for 7s400p or more eventually although each module of cells is only 100p for flexibility and weight.

I have been using a 100A Daly smart BMS for my current pack but have the parts for a DIY BMS for my new pack design. The Daly BMS can be a pain since it needs a charging jump start whenever it is first connected and sometimes when it triggers a safety shutoff.
 

win0911

New member
Joined
Sep 18, 2020
Messages
7
2400w/24v = 100a. Suggest a 125a or 150a 7s BMS. This is pretty mainstream and something like a DALY should work for you. This is just one suggestion - there are many in this 'lane' to choose from :)
Hi.
Could I know how to calculate to determine the capacity of the BMS to use?
 

Zwy

New member
Joined
Nov 29, 2021
Messages
4
Hi,
Let me describe my project and I need help deciding what BMS to go with. I am planning on making a Powerwall to power some external devices. The inverter I chose would be a MPP LV2424.
Batteries would be 18650s and I am planning on wiring them to that I would have blocks of 55 in parallel and then run 7 of those in series. This would give me enough voltage to run the 24v inverter. As of now we would be only pulling 1100 watts but would like to build the Powerwall to be able to take the full load of the 2400watts. What BMS would be good for a project like this?
Thanks for all the help in advance
I run the Growatt SPF3000 24V all in one in my truck camper. I used a Daly 250A Smart BMS on 280Ah LFP prismatic cells with it. My preference with any of the Chinese electronics is to run around 50% capacity. I don't see failures or surge shutdowns like others do.
 

OffGridInTheCity

Active member
Joined
Dec 15, 2018
Messages
1,863
Hi.
Could I know how to calculate to determine the capacity of the BMS to use?
BMSs do a couple of things - e.g. if they find something wrong the cut-off the battery from the circuit.
Here's the kind of things a BMS will check for / cut-off the battery if out of spec....
1) At a minimum they protect against charging and discharging too much.
2) They often include min/max temperature sensing.
3) They often include balancing - but not always.
4) They often include min/max current

It's #4 that where you need to buy a BMS that allows the max amount of current your need / your battery supports - which is expressed in amps coming in (charging) / out (load) of the battery. It's typically the load that is the key metric :)
 

win0911

New member
Joined
Sep 18, 2020
Messages
7
I run the Growatt SPF3000 24V all in one in my truck camper. I used a Daly 250A Smart BMS on 280Ah LFP prismatic cells with it. My preference with any of the Chinese electronics is to run around 50% capacity. I don't see failures or surge shutdowns like others do.
Wise decision
 

win0911

New member
Joined
Sep 18, 2020
Messages
7
BMSs do a couple of things - e.g. if they find something wrong the cut-off the battery from the circuit.
Here's the kind of things a BMS will check for / cut-off the battery if out of spec....
1) At a minimum they protect against charging and discharging too much.
2) They often include min/max temperature sensing.
3) They often include balancing - but not always.
4) They often include min/max current

It's #4 that where you need to buy a BMS that allows the max amount of current your need / your battery supports - which is expressed in amps coming in (charging) / out (load) of the battery. It's typically the load that is the key metric :)
I will learn the lesson soon by doing calculations for my future DIY batteries
 
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