Need help building a 24V Li-ion pack

[Tony Stewart]

Looks good. Got a good Quadcopter to go with it?

 

[audioguru]

The battery University says that 18650 laptop cells are LiCo02 (Lithium Cobalt Oxide) and other chemistries. A LiPo is also a LiCo02 cell mainly but with a different electrolyte. They all have a maximum charging voltage of 4.20V.
A LiFePO4 (Lithium Iron Phosphate) cell is different with a maximum charging voltage of only 3.65V. It might explode or catch on fire if it is charged to 4.20V with the wrong switch setting. OOps the cat bumped the switch and caused the explosion. But this project uses 4.20V cells and will simply get a low charge or no more charge if the switch is bumped to the wrong LiFe setting.

It looks like if a cell is much better than the other cells and needs more than 200mA of a discharge to match the voltage of the other cells (balancing) while charging then the charger stops or the battery cell smokes (the spec's do not say).

EDIT:
Maybe I understand charging balancing backwards. A weak cell will have a low capacity and will charge to 4.20V before the good cells that have normally high capacity. Then it needs to have its charging current bypassed until the voltage of the good cells matches its voltage.

 

[tcmtech]

Nice find TCM

spec

This is what happens when the proper information is given. A person gets workable replies that are not based on speculation and half-assed guesswork.

Looks good. Got a good Quadcopter to go with it?

No, I am starting to get a collection fo lithium battery based stuff around here and some of it runs on higher voltages so I need a unit that can work with batteries that are in the 6 - 8 cell 20 - 24 volt range.

 

[spec]

This is what happens when the proper information is given. A person gets workable replies that are not based on speculation and half-assed guesswork.

Get off your high horse tcm- you didn't have a clue what the OP was asking until I resolved the situation. If you are so thorough why didn't you confirm the battery pack configuration yourself.

There is no need for all the innuendo and circular arguments- try being direct and specific.

spec

 

[tcmtech]

Exactly! how many posts until the design was resolved when it could have been easily described much earlier.

You assumed he was running 6 - 8 battery strings in parallel. I was assuming he was running one string with 6 - 8 cells paralleled to work as one bigger cell per stage since he wanted to only run one charge control system rather than 6 - 8 of them.

As his first post describes, the wording is a bit ambiguous, but as his picture of the charge controller shows I took it to mean he wants to use one charge controller to charge multiple cells in place of each single cell as represented in the diagram.

As far as my high horse goes, well he did see what I was talking about at the end and how it would save him a load of work and money to implement with one single charge control device (as I found as well) so I find it quite justified.

 

[protocol217]

Thanks a lot for all the help, and sorry for lack of information in the first few posts, next time will do better.

 

[tcmtech]

It's okay. It's just been one of those weeks.

I've been through similar and worse stuff on every forum I am on this last two weeks.

Apparently, the has been a worldwide breakdown in people's abilities to read, comprehend, and not get butt hurt over nothing of significance.