7S A123 26650 - Need some questions answered!

ESK8 Builds
21

Wouldn’t the BMS think there was only 6 cells? Also, the balance port would have a 6s connector not 7s.

22

The BMS would be made for 7S though. “7s lifepo4 bms”

The balance port on the BMS would have a 7S connector. Jinra is talking about laptop style charging though. The BMS will take care of balancing the cells.

23

So you are saying a 6s lipo/lithium ion charger + a 7S bms? I’d be interested to know if someone has tried this. Sounds good. Thanks for correcting me guys.

24

So a BMS like this perhaps? All though this one might be overkill since I wasn’t planning on using it to discharge. http://www.bestechpower.com/224v7spcmbmspcbforlifepo4batterypack/BMS-D138.html

And then just a normal 6s charger? It does seem harder to find 7s lifepo4 bms, so depending on how expensive they are, might not be worthwhile the hassle in the end…

25

Actually just found this one: http://www.batterysupports.com/24v-252v-7s-30a-7x-36v-lithium-ion-lipo-battery-bms-pcm-pcb-p-258.html

Says it’s applicable for 3.6V, so does that mean its good for lifepo4? How does it know to charge to 3.6V vs. 4.2V?

26

First one will work, second one will not. The second one balances to 4.2 per cell which will damage your lifepo4 cells.

If you want decent energy density, and safety, why not go for Samsung 25R’s? Each cell has a built in safety. I prefer li-ion cells since they’re more energy dense than LIFEPO4’s.

27

Thanks I thought the second one wouldn’t work. But just out of curiosity, why does it say:

_Applicable for _ 25.2V (3.6V * 7S) lithium battery & packs 25.9V (3.7V * 7S) lithium battery & packs 29.4V (4.2V * 7S) lithium battery & packs Lithium battery (Li-ion) Prismatic Lithium Polymer battery (Li-Po)

Would you say there is any difference in safety between Lifepo4 and Samsung 25Rs? The other reason though is because this is only 6s, not sure if the 25R’s will have enough amps…

28

25.2V (3.6V * 7S) lithium battery & packs

This is nominal voltage, not full charge. If you read the description below, it says it balance charges to 4.2v per cell which is not good for lifepo’s.

Series doesn’t have anything to do with discharge rate. If you need the amps you add more cells in parallel. So if you’re running 6s4p, you’d have 80A of continous output. 25R’s are very widely used in esk8 and other hobbies and are pretty much a gold standard for li-ion. They have higher energy density meaning they pack more punch for the space used.