I had an idea for an alternative to RC lipo for use in ebike batteries. Why not build small 18650 packs with approximately equal voltage and capacity to commonly used RC lipo packs (~5AH, 4s-6s) that have no BMS but do have balance wires and discharge wires just like lipo packs. You could use them to build larger ebike packs and charge/balance them just like lipo packs either by bulk charging or balance charging.
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The main reasons/advantages are as follows:
Some potential disadvantages are:
I am going to work on creating a few prototypes, maybe 4 packs of 6s2p. This initial mock up would be 6s and 5200mah:
I've got some jst-xh connectors on the way and then I'll be able to build some of these packs for testing. I think it could be a good missing link for ebike pack building. Testing will show me if I've missed any important considerations here.
View attachment 1
The main reasons/advantages are as follows:
- this gives modularity for pack building and breakdown, especially for stuffing into odd shaped bags
- makes replacing a bad cell group easier as you only throw out (or repair) a small ~12 cell pack instead of a 65+ cell pack
- gives lots of cell choice as there are more variants of 18650s than most other cell types
- would be physically smaller and lighter than most RC lipo packs of comparable capacity
- allows you to keep using your same charger and wiring if you already use lipo bricks
- safer than lipo
- longer life cycle than lipo
- could add plug-and-play external BMS via balance and discharge wires
Some potential disadvantages are:
- hard to match the power output of lipo without using very expensive 18650 cells
- requires spot welder to join cells without damaging them (soldering is possible but damages the cells)
- requires care to not overcharge or over discharge just like lipo (however without the same associated safety issues)
- not for novice ebike riders (just like lipo) as making parallel/series connections between bricks requires care and understanding.
I am going to work on creating a few prototypes, maybe 4 packs of 6s2p. This initial mock up would be 6s and 5200mah:
I've got some jst-xh connectors on the way and then I'll be able to build some of these packs for testing. I think it could be a good missing link for ebike pack building. Testing will show me if I've missed any important considerations here.