Smallest & Cheapest LiFePO4 Cell Bottom Balancer

Here is a shrunk version of my original automatic bottom balancing device

Automotive relay, 3 resistive wire from an old air dryer, and 2 small switches

A red flashing LED to show when we are  in drain mode 

Some welding

Resistors and switches close up

and the final product
There is an input for a 12V power supply, I used a solar charged 12V battery for that 

Now some testing with remaining LiFePO4 cells 

Power switch ON

View from the top

Added a little extra cover on the red wire to avoid damage from the resistor heating up

From the left side

From the right side

I later on added a little piece of aluminum to dissipate the heat a little bit more

The resistors are going up to 75°C and more or less 4A are going through them :

Measured Resistance: 0.8Ohms 

Current: I = U / R = 3.2 / 0.8 = 4 Amps

It works fine and I drained one cell yesterday with it, in 2 hours I think

The total cost is close to 60 USD:

Programmable dual relay voltmeter                                             47.50

Automotive relay 12V / 30A                                                        3

Red flashing LED                                                                         5

Switches (x2)                                                                               2

Resistive wires                                                                              free

Wires and connections                                                                  3

Battery Clamps                                                                             free

Japanese fishcake board                                                               free 

                                                                                                 -------

Total                                                                                          60.5 USD

LiFePO4 Battery Pack Bottom Balancing Tool

A little video of my automatic bottom balance device