What is a BMS (Battery Management System) 2021

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BMS(Battery management system)
As more and more people start to switch from lead-acid batteries to lifepo4 batteries, BMS becomes the first problem they encounter.
“What is the BMS?”
“Do I necessarily need a BMS?”
“Why I need a BMS?”
…
These questions are often overwhelming for beginners.
In this article, we try to answer all your questions about BMS.
 

What is BMS?

A Battery Management System (BMS) is a electronic system that manages a rechargeable battery (cell or battery pack), such as by protecting the battery from operating outside its safe operating area, monitoring its state, calculating secondary data, reporting that data, controlling its environment, authenticating it and / or balancing it.
It is the brain behind the battery and plays a critical role in its levels of safety, performance, charge rates, and longevity.
 

Why I need a BMS for lifepo4 battery?

Many users who previously used lead-acid batteries had this question when they first switched to lifepo4 batteries: “Why do I not need BMS when I use lead-acid batteries, but I need BMS when I use lifepo4 batteries?”
 

Why don’t lead-acid batterys need BMS?

Lead-acid batterys are far less likely to burst into flames if something goes wrong with charging or discharging, simply because their ingredients are less flammable. But the main reason relates to how the cells behave after they are fully charged. Lead-acid batteries are also made up of cells in series; if one cell is slightly more charged than the others, and therefore gets fully charged before the others, it will simply pass current through the cell while remaining at a reasonable voltage while the other cells catch up. In this way the cells are “self-equalising” when charging. 
 
So normally lead-acid batteries do not need a BMS.
 

Why do lifepo4 batterys need BMS?

Lifepo4 batterys are the opposite: when a cell is fully charged, the voltage rises quickly and can reach dangerous levels. If this happens in only one cell, that cell can reach dangerous voltages before the total pack voltage is high enough to register as fully charged. Thus controlling and monitoring the total voltage of the pack is not sufficient for lithium-based chemistries, as you need to check the voltage of every individual cell making up that pack – this is done by the BMS.
 
So if you want to ensure that your lithium battery pack is safe and lasts for a long time – you do need a quality and reliable battery management system.
 

What are the functions of BMS? 

  • Protects the battery pack
  • Intelligent balances all the cells
  • Calculates the states of of charge
  • Monitors the health and safety of the battery pack
  • Provide the real-time information
  • Monitors the temperature of battery pack
 

How BMS works?

  • Protects the battery pack

It protects the battery pack from being over-charged (cell voltages going too high) or over-discharged (cell voltages going too low) thereby extending the life of the battery pack. It does this by constantly monitoring every cell in the battery pack and calculating exactly how much current can safely go in (source, charge) and come out (load, discharge) of the battery pack without damaging it. These calculated current limits are then sent to the source (typically a battery charger) and load (motor controller, power inverter, etc), which are responsible for respecting these limits.

  • Intelligent balances all the cells

Balances all the cells in the battery pack by intelligently bleeding off excess energy from cells that are charged more than others. This provides the maximum amount of usable energy (capacity) from the battery pack since the pack is only as strong as the weakest cell.

  • Calculates the states of of charge

It calculates the State of Charge (the amount of energy remaining in the battery) by tracking how much energy goes in and out of the battery pack and by monitoring cell voltages. This value can be thought of as a fuel gauge indicating how much battery power is left in the pack.

  • Monitors the health and safety of the battery pack

It monitors the health and safety of the battery pack by constantly checking for shorts, loose connections,  breakdowns in wire insulation, and weak or defective battery cells that need to be replaced.

  • Provide the real-time information
Provides real-time information and values to other devices such as motor controllers, chargers, displays and data loggers using several different methods (CANBUS, analog outputs, and digital outputs).
 
  • Monitors the temperature of battery pack
Monitors the temperature of the battery pack and controls a battery fan to regulate the temperature of the pack. Additionally, it constantly monitors the output of the fan to make sure it is working properly.
 
 
bms block

How to choose BMS?

If you have a 12v battery pack and you want to run a 500w inverter, that’s 500w/12v = 41.7amp draw from the battery pack. 
Your BMS ‘amps’ is all about allowing amps from the battery to the inverter when the battery is OK and cutting off the flow when the battery pack not OK. A battery has a max amp draw as part of it’s specifications… your LifePO4(s) will have this number. If you put 4 of them in series – then the number from 1 battery (of the 4 in series) will be the max amps you should draw and you should purchase a BMS with that as a key factor.
In this 4s battery pack example, if the maximum current of one of the cells is 100 amps, then you need to purchase a BMS with a maximum amperage of more than 100 amps
 
.In addition to this, you need to consider future expansions that may be used, such as the number of batteries you may add in the future.
 
 

What are the trustworthy BMS

BMS(Battery management system)
  • Includes a Bluetooth communication module.
  • BMS For 4 cell, 12v volt Lithium-iron-phosphate DIY batteries
  • 120 amp continuous charge or discharge current
  • Low Temperature Charging cutoff at -1c
  • Fully programmable with IOS app, Android app, or Desktop app
PRODUCT PAGE
  • Includes a Bluetooth communication module.
  • BMS For 4 cell, 12v volt Lithium-iron-phosphate DIY batteries
  • 120 amp continuous charge or discharge current
  • Low Temperature Charging cutoff at -1c
  • Fully programmable with IOS app, Android app, or Desktop app
PRODUCT PAGE
  • Includes a Bluetooth communication module.
  • BMS For 16 cell, 48v volt Lithium-iron-phosphate DIY batteries
  • 100 amp continuous charge or discharge current
  • Low Temperature Charging cutoff at 0c
  • Fully programmable with IOS app, Android app, or Desktop app
PRODUCT PAGE
Sarah O'Connell

Sarah O'Connell

As a research member with a background as an engineer, Sarah believes we need to know enough about products before we buy and use them, especially those that require some expertise and ability to operate. Sarah is happy to share her opinion and what she has learned with everyone. She believes that conscious consumption is everyone's responsibility and that all content should be complete.

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