Is it possible to replace segways 73.6 lifepo4 battery with Li-Ion cells ?

[Adam_0326]

Hello everyone, I’m brand new to the group but would consider myself to be quite experienced with electronics. I build custom batteries of all sorts as a side job and one of my customers asked me if I could rebuild a 73.6v Segway battery for him. My issue is that I have thousands of 18650 lithium ion cells on hand but I don’t have any 18650 lifepo4 cells.

Obviously the voltage ratings are both completely different for each battery chemistry so the current lifepo4 bms wouldn’t be compatible when using the lithium ion cells. I was thinking I’d use 72 individual Li-Ion cells to make a total of 18 cells (4P18S) (75.6v) rather than the 92 individual lifepo4 cells that make a total of 23 cells (4P23S) (73.6v). What I’m confused about is the 5 wires that go from the bms directly to the connector. I’m guessing that it’s some sort of communication link from the bms to the actual Segway ? Has anyone ever done this before ? I haven’t gotten started on this project yet because I want to be sure I’m not going to be causing any damage. Any advice or knowledge would be much appreciated. Thank you!

 

[floydr]

At 18s you would be way low in voltage both nom 66.7V and max voltage 75.6V. vs 23s nom 73.6V max voltage 83.95V. Besides what the communication problem may be.
Later floyd

 

[amberwolf]

Before you do any work on the battery, you may want to research other people's results, if anyone has ever published any on the web.
There are some OEM batteries from various companies that brick themselves if any serious fault condition occurs, such as a cell dropping below a protection level. That will happen when the cells are disconnected for replacement, for instance (the BMS will see 0v), so if the BMS has such a brick-fault-protection you'd need to wire up the new cells before disconnecting the old.

Some OEM batteries also track the capacity of the cells as they age, and "know" how much it has left; replacing the cells or adding more in parallel with the originals doesn't increase the capacity because the BMS turns off when it thinks it should be empty. The factory can probably recalibrate it, but there's probably no end-user software for that. ***

***I had an old laptop that had a capacity-tracking function in the battery and BIOS, and the battery wasn't user-replaceable. I replaced the cells, being careful to never disconnect the old until the new were in place, just in case, but the laptop would still shutdown when it thought the cells were empty even when they were still half full, and the battery meter reported the low capacity too. There was a recalibration function in the BIOS but it was grayed out, not accessible without the proper password or key when booting up I guess.


If the system requires comms between BMS and system, then you can't replace the BMS with a generic, so you can't use a different chemistry.