A typical LFP or
LiFePO4 cell has 3.2V nominal voltage which means that if you connect 4 LFP cells
in series you’ll have a 12.8V battery pack. The charge end voltage for a 4S
pack would be 4×3.65V= 14.6V but as you know battery packs need to be balanced to serve
for a long time, especially if the cells have different internal resistance.
Specifications
of HX-JH-004 4S LFP balancer board
● Dimensions (LWH): 26×20.5×2.4mm
● Balancing current for each cell: 58mA
● Balancing voltage for each cell: 3.60V (14.4V for the 4S Li
Let’s take a closer look at the components on the PCB.
There are 4 channels with identical set of elements the biggest one of which is the 62Ω resistor (marked 620) which defines the 58mA balancing (discharging) current.
Next comes a H&M Semi HM2302A (datasheet) n-channel power MOSFET in SOT-23-3L package with A2SHB marking, a Hycon HY2212-BB3A (datasheet) battery charge balance IC in SOT-23-6 package (marked AB3A M60J), an SMD capacitor and a 100Ω SMD resistor (marked 101).
Wiring the board to a 4S battery pack
For those who are going to build a pack for the first time here is the wiring scheme:
I’ve used 0.5mm copper wire for wiring.
The PCB with soldered wires looked like this:
I used a holder for 4×18650-size cells and I intentionally used different cells with different internal resistance to complicate the job for the balancer.
Testing
The measurements showed that the balancing current was 58-59mA which is exactly what the specs tell. I’ve repeated the test 3 times. Between charging and balancing a 1-hour pause was left to have stable voltages of the cells.
Ch – number of channel of the balancer
Cell – number of cell
Before – cell voltage before balancing
After – cell voltage after balancing
Δ – the difference with 3.6V for a cell and the difference with 14.4V for the pack
ROUND 1
|
||||
Ch
|
Cell
|
Before
|
After
|
Δ
|
1
|
1
|
3.768
|
3.600
|
0.000
|
2
|
2
|
3.625
|
3.596
|
0.004
|
3
|
3
|
3.725
|
3.595
|
0.005
|
4
|
4
|
3.707
|
3.584
|
0.016
|
Pack V after
balancing: 14.375
|
0.025
|
|||
ROUND 2
|
||||
Ch
|
Cell
|
Before
|
After
|
Δ
|
1
|
1
|
3.697
|
3.600
|
0.000
|
2
|
2
|
3.685
|
3.595
|
0.005
|
3
|
3
|
3.663
|
3.596
|
0.004
|
4
|
4
|
3.683
|
3.583
|
0.017
|
Pack V after
balancing: 14.374
|
0.026
|
|||
In round 3 I’ve swapped the 1st and 4th cells to exclude the impact of a cell-channel combination.
ROUND 3
|
||||
Ch
|
Cell
|
Before
|
After
|
Δ
|
1
|
4
|
3.691
|
3.598
|
0.002
|
2
|
2
|
3.692
|
3.599
|
0.001
|
3
|
3
|
3.678
|
3.595
|
0.005
|
4
|
1
|
3.694
|
3.587
|
0.013
|
Pack V after
balancing: 14.379
|
0.021
|
|||
In the first two rounds the cell on the first channel was discharged down to 3.600V which looks pretty nice. The next two channels were below 3.6V by 0.004-0.005V which is a miserable delta. Only the 4th channel was below 3.6V by 0.016-0.017V which is not as low as the other channels but still a good result.
The 3rd round showed that the results don’t rely on cell-channel combination because the first channel with the cell №4 again showed almost no difference with 3.6V and the 4th channel’s delta was again higher than 0.01V – 0.013V to be exact.
Upgrade
During balancing the 62Ω resistors heat up the board up to 60°C. To cool it down I took a couple of 9×9×5mm heatsinks and cut the ribs to 2.1mm
I attached them together by putting a sticky insulation tape on long sides. It’s very important to use insulation to avoid contact between the heatsink and resistors.
Then I applied some thin layer of thermal conductive glue to resistors.
And accurately put the heatsink on to the resistors and left to cure for several hours.
This upgrade helped to lower the temperature by 8-10°C.
Verdict
So, this balancer is not bad at all. The first 3 channels’ accuracy is between 0-0.005V and only the last channel showed 0.013-0.017V difference with 3.6V target voltage. The balancing current is 58-59mA which is also quite accurate. The high operating temperature is something I didn’t like and put an aluminium heatsink but even without that additional cooling the board will work fine. I took it for $1.5 which is not a too high price for such a performer.
Here is the video version of this review:
