4PCS 3S 40A BMS 11.1V 12V 12.6V 18650 Lithium Battery Protection Board with Balance Li-ion Lithium Battery Charger PCB BMS Lipo Cell Module for Drill Motor

Finally a decent BMS for Inductive loads (motors, halogens, etc)! So far discharge is working perfectly. My only complaint is that they didn't use a single inline row of pins so a connector could be mounted to the board for the balance leads so they are spread out all over the place. But I wired it up with my own connectors. Works great so far, will update if any issues. I also wish these inexpensive BMS boards would allow/document some selection to alter the charge and discharge limits, perhaps replacing a resistor, using jumpers, or using a 10-turn Potentiometer.

I was building a air horn using an old screwgun I had laying around. I had to build the battery for it since the original ni-cad battery was dead. I replaced them with four 21700 lithium ion batteries and this bms and it fit perfectly. I had a 20amp 4s bms laying around so I tried it first. The current draw smoked it pretty quick. So I bought these 40 amp BMS. I know the air horn pulls at least 15amps, not sure of surge current. The holes in the soldering pads for the + and - output accepts a 14awg wire as well as the battery + and - inputs. For the sense leads I used 18awg.I would buy these again.

I would say the larger value is the price as I will be adding voltage indication. I would give it 5+* if it had a charging and charged status output. But I’m glad to have what i purchased seems to be working, so far, but after testing I cannot figure out the two pads left opens use. “Fc,**” this is a mobile application so extra devices aren’t appreciated. Over all happy though so far.

Update: Go find your BMS somewhere else. Skip this seller and skip Amazon. 100% of the BMS I buy on Amazon as of later are failures. Some brands of BMS on Amazon never work and others once you put them in actual use.I just had two fail being charged during testing using a benchtop power supply at the correct voltage and low amps. I was simply trying to test the BMS. Both failed withing seconds. I didn't get around to trying these until the return window was closed. Between these and several others, I'm big time in the hole.Dear Amazon - you suck as of late. Slow deliveries and shoddy products. I may as well buy off of Ali Baba direct at this point. Maye do the right thing and allow me to get my money back?

I used these to convert a ni-cad battery to a 18650 lithium pack for a drill/saw combo. The install and first complete charge-discharge-charge cycle has gone well. I don't expect to get anywhere near the 40 amp limit on these, but I am confident this battery will work well no matter how hard it is pushed.

Fits my home made lithium 12 V 3S battery nicely. The electrodes for connection all lined up perfectly for connection to my 3S 12 volt battery. See photo of finished battery with the BMS installed.

The installation of these BMS was easy and straightforward. Hiwevre these BMS so far do not work with solar charge controllers. Initially I though there was a problem with the controller so I purchased another and it was the same problem. As soon as I bypass the board the battery started charging I'm monitoring the charging progress.

One out of the four failed to function at all. A second one I destroyed by accident. The remaining two function well.