Just to protoype this we have over $4k invested.... and that is just in V4.0
The back button will show you V3.0, V2.0, V1.0, and the year of education by fire it took before that.
The BMS you see for $75 is nothing compared to a full featured system. Things like cell level datalogging, temperature compensation, expansion capability, re-programmability, isolated communications/compatibility with other systems, a software package.... To the customers we are looking at this is an incredible bargain.
Ignore the silk... I just ran up against the clock
What you are looking at from left to right in the bottom picture is:
*Satellite for master with connectors and relays (Satellites are customer specific so we dont have to change the main board)
*PWM section - this one should be good to 150V 60A and it has a built in +/-100A hall for monitoring charge current.
(Master stacks on top of PWM. Electrically isolated + small shield. Satellite extends away on two 25pin flat-flex cables)
Then the duplicated pairs are the slave boards with the LTC chips along with their respective satellite boards... again... so we can change connection schemes without changing the main board. It also allows us to fully pot the slave and makes it smaller and easier to mount to the frame
The shunts are 20W TO126 and we are running them at >2A
PWM section has 4 x IRFB4115 fets and enough 250V 1.2uF ceramic caps to make you cringe. This time we also have some large Schottky diodes in there for isolation.