I need some help with rebuilding a 7.4v lipo battery pack for a coworker’s drone that you can’t buy parts for anymore. It all started when my coworker brought in the battery pack with charger saying that the charger just kept flashing the red light when he plugged it into a usb port. I started trying to figure out what was wrong with it by poking around with a DMM and figured out one of the lipo cells was totally dead. I then went online and found 2 new lipo cells of about the same mAh rating and soldered them in, still didn’t charge the batteries. I then ordered a new Lithium Li-ion Battery Charger BMS Protection PCB Board figuring maybe it had gone bad when the dead cell did. I just soldered in the new board according to the ebay listings picture of the wiring diagram. I plugged it into the charger and still same results, red light flashes. Does anyone here have any knowledge/experience with this kind of thing? I hooked up the batteries like the attached picture below. I measure 3.8v~ between BM and B-/B+ and 7.4v~ between B-/B, but no voltage between P-/P. Should I be able to measure voltage at P-/P+?
@yuvals Is the picture I posted in my first post not visible to everyone? I can see it?
@chops728 your diagram is a little different than the circuit board I ordered. I have attached some pictures to hopefully help.
This is the new batteries soldered onto the old circuit board, ignore the smaller jumper wires I soldered on when I was trying to figure out why it wasn’t working.
This is the new circuit board soldered onto the new batteries, I am still using the original connector as I need it so it plugs into the actual drone.
This is the charger that came with the battery, no model or serial number and I can not find it anywhere for sale.
Your measurements between B-/BM and BM/B+ are correct —— not sure why you’re not getting voltage at P-/P+ —— sometimes you have to put voltage to the P-/P+ to wake up the BMS —— Also you’re using the old board for the plug — are you sure have voltage across the 2 pads you soldered to on the old board when trying to charge the battery
Also why do you have that blue wire going to the old board — with the new BMS you shouldn’t need that hooked up
If you had an adjustable power supply, you could tap into the P-/P+ wires and set it to 8- 8.4volts to see if it charges
I just copied what was there before hence the blue wire, I will take it all home with me and try what you have suggested as I have a power supply there that will work to test it all out. If it turns out to be the charger isn’t working as well can I charge the battery pack if I supply it with the 8.8vdc 1.8a or do I need to have a proper lipo charger?
You should be able to charge with your power supply 8.4 volts max — I would start out at 7.8-8 v and monitor the cells to make sure they are balancing correctly
Make sure you set the voltage on the PS before connecting to the battery
Ok so I have successfully charged the battery pack with my power supply at home. Now my question is how to charge this battery once I give it back to my coworker, anyone have a suggestion?
I charged the battery from the positive and negative on the drone connection which is basically the P+ and P- on the new circuit board as seen in the pictures above. I charged at a maximum of 8.4V at 500mA while making sure the batteries didn’t get hot and charged evenly.
So you know the connector is letting the charge in —- I would think the original charger is dead or some lind of way isn’t being told to charge the cells — you could just make up a new charger with 2 cell charger and just put the old charge connector on it
