Advantage to BMS transfering battery load?

I'm looking to build my first battery.

I've noticed some BMS's, like Daly, will have leads and all the system load will transfer through the BMS.

Others, like REC BMS, only have sensor leads to monitor cells, and don't carry the system load.

Are there advantages to one style over the other? I assume those that carry the load (Daly) pass it through an internal shunt to better measure current. If true, do the REC-style ones have noticeably worse SOC monitoring?

Are there other key differences in the different BMSs?

Yes. Contactor BMS are more efficient and handle higher currents, at the cost higher cost and more design complexity.

You also have to be more careful with contactors as they don't have unlimited operations, it wears them out to open under load so you really want to avoid the BMS ever routinely or repeatedly having to interrupt.

The external shunt or sensor on a contactor BMS is not necessarily better or worse than the internal one on a FET BMS. In most cases, it's likely better. It all depends on the quality of the sensor.

All of the popular BMS products discussed on the forum do not have an internal shunt therefore are not high precision devices with regard to SoC. This is one of the main complaints mentioned.

There are 3 ways to control the DC system load.
1) Power FETS on the BMS PCB. There are 2 sets, 1 for charging and 1 for discharging.
2) High amperage Contactor
3) Remote Trip DC breaker.

hwy17 said:

The external shunt or sensor on a contactor BMS is not necessarily better or worse than the internal one on a FET BMS. In most cases, it's likely better. It all depends on the quality of the sensor.

Click to expand...

The ADC is a big part of this issue. A typical microcontroller is only 8 to 12 bits which doesn't afford enough resolution to capture small standby currents. I've experimented with a 20 bit TI INA229 shunt monitor and it is super accurate but it costs a couple of dollars all by itself.