… a continuation from part 1.

When putting on the cell boards boards on the cells I was extra careful to not let the wires touch anything or to put the board on backwards. Each board’s LED blinks 3 times when you plug it in. I had two dead boards that didn’t blink when I plugged them in, so I had to get two replacements from Evolve Electrics. One clearly had a bad solder job, but I don’t know what was up with the other one.

Wiring the BMS was pretty much straight forward. Crimping was tough — I bought two crimpers from frys and by using both of them I could get a good crimp. If I were to do it again I probably would try to buy a better one online.

The BMS doesn’t support the Netgain controller yet. Eventually it will limit voltage to the controller when the battery gets low, but for now I wired up the LLIM (low limit) to a 12 volt buzzer.

After the BMS is all wired up, one must do the setup. Here is where I had some confusion. The setup page is pretty sparse and non-specific on what you need to do. In particular, this line

> 1.If the cells are other than LiFePO4, program the cell voltages

I thought Thunder Sky batteries were pretty much LiFePO4, so I incorrectly assumed I should use the BMS values for the LiFePO4, but that was a bad assumption! It would be nice if the setup page said exactly what to do for exactly what brands of cells; that would have made it easier for me. ThunderSky cells are LiFeYPO4 (some Yttrium thrown in) and have a difference chemistry and need a different charge setup. Davide told me on the forum to use.

V-cell-max: 4.0 V

V-cell-high and V-min-balance: 3.5 V

V-cell-low: 3.0 V

V-cell-min: 2.8 V

I’m using a V-cell-max of 3.8 or 3.9 (I forget which one at the moment, as I switched them back and forth), since other recommendations say to not charger higher than 3.8 volts, as there is little to no extra energy in that range. So, my initial charge took a long time; partially because the balance voltage was set too low, and the cells were constantly trying to balance earlier then they should.

Another problem I had was setting the current sensor direction. I’m using only one current sensor for both charge and discharge, and the direction option was confusing me. The arrow should always point into the battery, and if it is you say YES to the setting for current direction (or NO if it points out). I thought the arrow was for the flow of current, so I thought I had to flip the value for one of the two settings. It turns out that wasn’t the case.

The next problem I had was the “State of Health” of the cells was poor — like 52%. It still seems to vary when I charge, especially if the cells shunt excess current for a while, but it is definitely better than before. That seemed to be because the current sensor wasn’t “zeroed out”. More details on this thread.

I’m still getting some other warnings, such as charge over-current. I need to finish looking into those, but they don’t seem to bad.

I also tried using a different 50amp current sensor for charging, but I couldn’t get it to work for some reason, despite having the information and diagram from this thread.

One other important note in testing the BMS. The directions clearly state it, but don’t forget to do a “HOME / Test / Release Outputs” after doing a test operation. I thought setting it back to the original value would be okay — but it isn’t! On my second test charge the voltage of the cells crept up to 4.1 on a cell before I flipped off the charger manually. It took me a minute to realize that the BMS wasn’t turning off the charger because I left the output on. Doubt!

The BMS is pretty cool, although quite complicated. I’m still working out how to get my fuel gauge working. More on that later…(once Jason helps me figure it out!)

Previous Post

Plug Bug: IOTA DC-DC Converter fix

Next Post

Plug Bug: Unicycle Storage