How to fix a broken 30K lithium-ion battery

Last time I posted about my broken 30K lithium-ion battery pack from LEED. Years ago, I also posted about my broken SLA battery pack from Clean Republic. Both packs are actually easy to fix if you know how the parts work.

It turns out that in both cases, the problem tends to be the connectors. The DIN connectors of the SLA battery pack gets so overheated that the solders melt. The controller sometimes burn out because of the heat as well.

The most recent connector problem with my 30K lithium-ion battery pack, as it turns out, is due to the Dean T connector (female plug connecting the battery and the controller) burning out. I never heard of this but I discovered that this was the problem why my battery pack is fully charged and yet no power comes out of the pack. The positive plug of the female Dean connector show signs of burned surface.

close-up view of the burnt female plug positive hole

multitester reading zero on the positive hole of the Deans T connector plug

I simply replaced the Dean T connector and it fixed the problem. My 30K lithium-ion cells are still alive. They should since these are Samsung cells that are rated 1500 charge cycles. They still have about 1150 cycles left so they should last for years to come.

Building a better pack with serviceable parts

Imagine a broken 40 cent Deans T connector causing you to buy a new 30K battery pack that costs at least 400 dollars? If users know how to fix their own pack they could save time, shipping money and effort.

I suggested to dealers that they provide the option to service parts but they don't see that such an option is profitable. Users are therefore left to DIY this option. Like this new DIY built 10K pack with removable 18650 Li-ion cells.

To the right is my DIY pack with removable cells that are 26,000 mAH each (Samsung ICR18650 26F). The device on the left is an inverter that converts the 24V DC given out by the pack to 110V AC that powers the computer I use to write this blog.  The pack can power my 45W computer for 5 extra hours. The pack can also power my e-bike motor kit. 

Why make the 18650 cells removable?

1. Commercially available battery packs have the battery cells parallel connected, thus, these cells  cannot be truly balanced. By making the cells removable, it is possible to check each cell using a balance changer.
2. It makes it easier to replace the broken connectors and failing cells instead of replacing the whole pack (when cells are soldered together).
3. Users learn how to make their own pack by being familiar with the parts and their function.
4. It is fun to make.  

Here is what is inside the DIY pack:

The schematic diagram for the balancing wires are shown below. This is based on the reverse-engineered connections of my old Sprinter battery pack assembly from Clean Republic.

The next time my battery pack breaks down, I know how to fix it. It is possible to get BMS board replacements from dealers. Controllers are available for 50 dollars each if these break down. The 18650 cells can be easily replaced by hand instead of having them permanently soldered to nickel plates.

This is a 7s2p battery pack configuration that the Clean Republic 10K Sprinter BMS supports. Note that the balancing wires are color-coded to make it easier to make sure the right wires are connected to the right plug. The positive and negative points of the 7 series (2 parallel) battery cells are connected to the BMS board which then balance outputs 25.9 V to the controller. The BMS also balance inputs charge to the battery cells in the series through 7 balancing wires. The BMS is like a mini balance charger for each of the parallel cell-couple in the series. The BMS board costs 25 dollars. The balancing wire white wire to board connector plugs are about 1 dollar per 10 pack set.

Remember: Before you declare your pack dead check the connectors first!

Word of advice that will save you hundreds of dollars and the trouble of sending back lithium-ion battery pack though the mail: test the connectors for burnt or melted points first before you declare your pack dead.