5PCS 2S 7.4V 8.4V 8A 18650 Charger PCB BMS Protection Board for Li-ion Lithium Battery Cell

So far, so good. Made a pack of 2x18650 in 2S configuration.voltage initially was zero, but just plugged in the charger, and it activated. Voltage output was about 8.14v (because the batteries were almost fully charged). Plugged in charger, light on charger was Red, then after about 1 minute it switched to 10.3v and the charger light went Green. Which is what I expected. Works great so far!

These little devices do exactly what they are supposed to - when they work. I received 5 of them and the first 2 did not function. Because I am stubborn, I did not give up and tried the remaining 3 and they functioned perfectly.These are really great when they work to protect the potential little battery bombs we use everywhere. Not so impressed with the quality control of the delivered devices and will buy from elsewhere when I need more.UPDATE: I lowered my rating to one star since out of the 3 that “worked” one of them would cut off the output voltage every 100mS when connected to a perfectly charged cell with a very light load. So 2 were initially dead, one is unusable with weird operation, and I certainly don’t trust the remaining 2 of the five I received, even though they seem to work - for now.

I picked this to test because of the High-current (8A max) output spec and simple design for isolating the batteries from external circuitry. It is tiny, fits easily in the curved space between two 18650 cells, or in the center of a block of four. My test build has the board shrink tubed between two cells. No problem with heat so far, but have not tested full load, or low-voltage cutoff situations.The charging circuit seems to work flawlessly. Input and output are just two wires (V+ and V-). Mine charges to approx 8.45v when line voltage is up to 9v (following specifications) and discharges when there is a load. This was using a 9v-2amp wall brick charging the two Li-Ion cells and also operating 24v LED from a boost circuit. Batteries fill in whatever the charger is unable to supply and keep the uninterrupted operation of the lights.I hope others can contribute information about designs to put these in series/parallel banks for 14.4 volt or higher for solar-PV energy storage, or maybe where to wire a charge indicator light to identify fault cells..

The media could not be loaded. I was pulling my hair out trying to figure out WHY! This BMS wasn't working. Then after reading other buyers review I found out that u must "initiate" the BMS. I did that and BAM! it started working.Ironically I designed this 20,000 mAh variable power supply to be free of houshold power to be used while traveling and or camping BUT I needed to plug it into a household outlet to initial the dang thing. Lol 😆 I find that ironic.Anyway, the BMS is up and doing its job. I do wish for led indicators, red for charging, green for cutoff voltage has been reached and a flashing red LED if a problem occurred. I would think that would be a simple adjustment to this somewhat simple design. Anyway I like the size! I am using to charge 21700 cells (I hope it works). Im still wiring the rest of the project so I will soon see if it works.I wil update with data.Dave C. Stout

I bought these some time ago, and finally got to the project that needs them. I set up the battery pack by itself, so I could test it independently. Once I inserted the four 18650's, I didn't get anything on the output. I ended up reverse engineering the board, and found one thing that concern me. And, after reading other reviews, I found a workaround for a board that doesn't have output voltage when batteries are connected.These boards were designed almost exactly like the example 4-cell circuit shown in the ABLIC S-8254A Battery Protection IC that the board is based on. The only change was to place two MOSFET's in parallel for each of the charge and discharge circuits. The reliance on the internal protection diodes in the MOSFET devices for charge/discharge reverse current flow leaves a lot to be desired. The datasheet for the AO4407A MOSFET's specify a maximum of -3 Amps for the internal diodes. Two in parallel, making a max of -6 amp for the boards. Stating that the board can handle 5 amps is not leaving much overhead. Due to this obvious shortcoming, when necessary, I will add another rectifier across the charge MOSFET pair to pass discharge current. Since I don't expect to be charging the pack at more than 3 amps, I won't need a rectifier across the discharge pair for the charge circuit.The board I am using in my current battery pack doesn't power up (supply voltage on the P+ and P- solder pads) when batteries are connected. Connecting a charger or a 16.5V power supply to the pads for less than a second will get the board working. I started out with fully charged 18650's, so 16.5V won't hurt anything. Once the batteries are in, and the board is working, it will not require a charger or power supply to kickstart the board unless batteries are removed.I haven't tested the board and batteries under load yet, nor have I charged batteries with it. However, after looking at the circuit, datasheets, and reading other reviews, I expect them to work just fine.Edit:I thought some might like a copy of the reverse engineered schematic of the board for troubleshooting purposes. The active parts are:Q1 - Q4 - AO4407A - Alpha & Omega SemiconductorU1 - S-8254A - Ablic Semiconductor