Measuring my last Mottcell LiFePO4 cells

As I already wrote few weeks ago, I made a 3 LiFePO4 cells pack with them, bottom balanced them, charged, and discharged them few times by plugging in an iPhone / iPad 12V charger, which downstages voltage to 5V anyways (so it does not have to be 12V really to work, it could be 2 cells actually)

Few days ago, around diner time, I checked the voltage of each cell, because it had been more than two weeks and we had been charging our iDevices on this mostly

You can see here the benefits of bottom balancing the cells before the first pack charge: we are reaching the lower limits of the cells and they are still in balance, coming down together:

Voltage measured still under load (iPhone is plugged in as you can see)

Cell 1 = 2.94V

Cell 2 = 2.93V

Cell 3 = 2.92V

Pack  = 8.80V

=> So, no problem, and after reffilling my iPhone fully, it will be time to recharge the pack 

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 ESS update - 1000W Produced and DC Breaker swap

I had a problem with this 100A DC breaker, that was not handling 100A, but breaking the battery pack after all my Grid Tie Inverters would come on for few minutes producing 1000W all together

So we have 1000W produced and fed by into the Grid, plus some heat wasted for each GTI, let's say 200W (?) more, all this coming from the battery pack energy: 1200W / 24V = 50A
So this breaker was more like a 50A DC breaker in the end ....

The not really 100A DC breaker

A real (I hope) 100A DC breaker from the Enginer Prius PHEV Kit 

New position (on the floor) for this new breaker

A bar of copper is linking the bottom to top cells groups

With this new real 100A DC breaker, the ESS can hold the produced 1000W for long periods of time without any problem :-)