You might get overwhelmed with different choices when looking for the best BMS for LiFePO4.
This article will make you pick the right one.
|Best Overall||Runner-up||Best Budget|
|JBD or Overkill Solar BMS
||JK BMS (Jikong)
|Best overall BMS because of good reliability, app usability, and support.||Best BMS for high active balance current but no low temp protection.||Best value for money but with a buggy app. No low temp protection.|
|5/5 ease of use||4/5 ease of use||3/5 ease of use|
|5/5 support||4/5 support||3/5 support|
|4.5/5 price||4/5 price||5/5 price|
Next, we will list the most used BMS’es for LiFePO4 batteries.
Best BMS for LiFePO4 Battery Cells
1. Overkill Solar or JBD BMS
Overkill Solar tests and calibrates each unit at their shop in Florida before shipping. They will also assemble the BMS with custom high-current wire and terminal configurations. They provide a warranty, thoroughly written documentation, and US-based tech support to DIY’ers.
Overkill Solar reached out to me and said they have a custom app for their BMS, which solves some well-known problems with the xiaoxiang app.
The balancing current is relatively low, so an initial top balance is advised. The app is very easy to navigate and adjust parameters. I recommend this BMS as a reliable but still a budget option.
2. JK smart BMS
The JK or JIKONG active balancer BMS is a great choice. Instead of wasting the balancing power as heat, it redistributes it to a lower-voltage cell. The app layout is easy to navigate, with many options. It comes with three temperature sensors for high and low-temperature cutoff. The BMS uses active balancing.
Daly has been a popular choice for many DIY’ers. Many people have chosen this brand because of the many guides you can find online. It has a vast range of options for you to choose from. It has smart options and standard options. The smart option work with Bluetooth and an app. The standard option is a plug-and-play version.
An important thing to mention with Daly is that while the discharge current is 100A, the charge current is only 50A. The balancing current is rather low at 30mA. Below you can see the spec sheets. It also has no low-temperature disconnect. A real turn-off when you live in a cold climate.
While testing this BMS on my pack, the app connectivity is buggy. It still works, but you have to be patient. The app store rates the app 1.7 stars out of 5, which says something.
4. REC BMS
REC is a Slovenian company that makes a reliable BMS. The BMS can be paired with a shunt and is Compatible with SMA sunny island. The standard REC Q BMS can be used up to 16S, and with the master unit, you can connect 240 cells in series. It also has a relay and digital outputs. The current doesn’t pass through this BMS like the DALY or JBD BMS.
Their customer support is good and compatible with Victron (cerbo GX), so you can have the battery shown on their display.
This BMS can be used with an alternator because its output can turn off a relay.
5. Batrium BMS
CellMate-K9 is the most recent version of their product line. The Batrium BMS is ideal for DIY powerwalls. With it’s many available expansions and great graphical interface, this BMS is a great option. The current doesn’t pass through this BMS like the DALY or JBD BMS.
Data logging for over 10 years with a built in clock. Additional input and outputs are available with expansion boards. You can extend the BMS if you want to add more cells to the system later.
The QUCC is a BMS that uses a relay instead of MOSFETs to break the circuit. This results in the cost being lower, but that doesn’t make it more reliable.
If you have a capacitor in your system from an inverter and the relay closes, the arc between the two contacts can cause both contacts to melt. This can prevent your relay from opening again.
BMS Buying Guide
How Do I Choose a BMS for LiFePO4?
Do you want to adjust the parameters in your BMS? If so, then choose a smart BMS. Most of the BMS’es you can find are smart.
Do you need a low-temperature cutoff? Having that kind of protection might be necessary if you live in a climate where it gets cold.
Is your battery pack top balanced? A BMS with a higher balancing current will be the best choice if it’s not top-balanced.
Do you value products made outside of China? If so, there are many options, but you will pay a higher price for them.
Read more about choosing a BMS for LiFePO4 here.
Do LiFePO4 batteries need a BMS?
If you are building a DIY battery, you should add a BMS. They can work without, because the cell voltages will drift away from each other over time.
At some point, this imbalance will cause the highest cell in the pack to be overcharged, which can be destroyed even though the total battery voltage is still normal.
That’s why you need a BMS with balancing and overvoltage cutoff.
If you buy a ready-made battery, the BMS will be included.
What is the difference between smart and dumb BMS?
A smart BMS connects to an app through Bluetooth, wifi, RS485, or a CAN connection. You can change the settings in the graphical interface. A standard or ‘dumb’ BMS is plug-and-play. The settings cannot be changed.
What is the difference between a switch BMS and a relay BMS?
A switch BMS uses MOSFETs to turn off the current. A relay BMS turns off the current with a relay. It’s worth noting that a relay is not always made to interrupt current as a breaker can. So the relay contacts can ‘stick’ to each other.
What is the difference between active and passive balancing?
Passive balancing will remove or add capacity from a particular cell and dissipate it as heat. Active balancing takes the excess from one cell and delivers it to a cell with a lower voltage. Active balancing has fewer losses -and is thus more efficient. read more about passive and active balancing here.
What size BMS should I use?
As mentioned in my other article, you should not go over 100 Amps in your system. If you do, you need to increase the voltage of your system. I still don’t understand why people would buy a 300A 12V BMS. It’s a waste of wiring costs and a safety hazard. Below are my recommended inverter sizes for a particular system voltage:
- 12V: inverter below 1,200W
- 24V: inverter below 2,400W
- 48V: inverter from 2,000W to 5,000W
Using these guidelines will not only save you on wiring costs, but it will also save you money on a BMS and a charge controller.
4S BMS LiFePO4 Diagram
Wiring a 4S 12V BMS is quite easy. The BMS has two cables. These are the main battery – and the main cell -.
Wire your 4 cells in series and then attach the 4 leads to every positive. Then connect the black wire to the main negative of cell 4.
In total, you need to connect 5 extra wires to the cells. Make sure you get them in the right order. This is usually described in the manual or on the BMS. These small wires are there to sense the voltage of every cell and charge/discharge them to balance them.
What current does my BMS need to be?
Let’s assume you have a 1000W inverter; then your current requirement will be:
We then need to include some headroom so the BMS doesn’t work 100%; this can lead to overheating.
In this case, with a 12V battery and a 1000W inverter, you need a 100A 4S BMS.
I recommend keeping the current at or under 100A.
If you have a 3000W inverter, then you should use a 48V system.
3000W/12V= 250A -> too high
3000W/48V= 62.5A -> ideal
JK vs Daly BMS
People often ask me what BMS they should get. A Daly or JK BMS. I always recommend people to get the JK BMS for the following reasons:
- JK has better support
- Higher balance current (0.6A for 100A version)
- Possibility to add heating pad
- A 100A-rated daly BMS will have a 50A charge current. JK has a 100A charge/discharge current.
Does Victron have a BMS?
Victron Energy does not have a BMS for custom batteries. They do have a BMS for their batteries and a battery balancer (more info here).
In short, Victron does not offer a smart BMS for DIY batteries.