Charging 18650 LiIon and LiFePo4 Question.

[rizky_p]

Hi, which one is safer charging 18650 in paralel or serial? i am using unprotected Sanyo 18650.

Can i safely charge LiFe 18650 in serial or paralel?

thanks.

 

[mdocod]

Re: Charging 18650 and Life Question.

standard lithium cobalt oxide cells can be charged in parallel with pretty good results, they tend to balance as they charge when in parallel because voltage and state of charge are in direct relation, so the voltage tends to balance between the cells, but only cells that are in a similar state of charge (or discharge) should be charged together this way. Serial charging of these cells is not recommended UNLESS it is only used to charge up to a point, (like say 4.0V per cell) and then the pack is "balanced" cell by cell after the fact (topping up to ~4.20V per cell)

Lithium Iron Phosphate cells are probably more well suited to serial charging as they tolerate overcharge more like Nickel based rechargeable cells (they just heat up as overcharged, but don't become dangerous), just charge to ~3.8V worth per cell and they will balance out reasonably well. You can extend cycle life by balance charging LiFeP04 packs, but it is not absolutely necessary as the chemistry is safe.

 

[rizky_p]

Re: Charging 18650 and Life Question.

thanks, I was trying to charge 3 18650 LiIon pack which has exactly the same age and wear. charging them 1 by 1 just time consuming so decided to paralel charge them.

When in 1S3P configuration is that mean i can increase charging current by 3 folds?

 

[saeckereier]

Re: Charging 18650 and Life Question.

PLEASE if you talk about the different battery/cell types use the adequate terms. Everytime something starts a thread like this they feel like leaving out some part of the name doesn't matter, but it does.

Usually they're referred to like this:

LiIon - The well-known standard Lithium Rechargables (in detail: Lithium Cobalt Oxide)

LiPo - Lithium Polymer cells used in RC applications, fast charging, very flat cells, even more dangerous than LiIon

LiFePo4 - (or LiFePo but not LiPo or LiFe) Lithium Iron Phosphate cells, the newest variant on the block, safe chemistry, less capacity, high discharge rates available

It would be so nice if we didn't see the same happening as with CR123As, two more letters really aren't so hard to type and make a hell of a difference here..
Don't want to offend you, but it really makes it so lot easier..

EDIT: BIG thanks to mdocod for *always* using an unmistakeable wording

 

[yellow]

If You put single cells in parallel without further "equipment" (= a resistor)
You pretty much have a short till the voltage is the same on the cells!

 

[saeckereier]

Re: Charging 18650 and Life Question.

If You put single cells in parallel without further "equipment" (= a resistor)
You pretty much have a short till the voltage is the same on the cells!

I think you perhaps mean Serial? Parallel is connecting both + to one wire and both - to another..
EDIT: As for the other one, you don't have a short until voltages are equal, you are actually shorting them out completely, but without a resistor and only cable you're usually doing that anyways.. Can you perhaps clarify your post, I'm confused.. 8-|

 

[DM51]

Re: Charging 18650 and Life Question.

I think you perhaps mean Serial?

No. When you connect 2 cells of different voltages in parallel (+ve to +ve and -ve to -ve), there is an instant flow of charge from the higher one to the lower, until they achieve balance. Effectively, the higher cell is charging up the lower cell.

This current flow can initially be at a very high rate indeed, but the voltage of the higher cell will quickly sag and the current will then settle down to a more reasonable rate, dropping all the time, with the cells eventually achieving full balance after ~15 minutes or so.

Li-Ion cells can tolerate high current in short bursts, but connecting 2 cells in parallel should not be attempted if the voltage difference between the cells is more than 0.5 volts.

 

[rizky_p]

@saeckereier: thanks for pointing the issue.

tried charging 3 18650 in paralel it works nicely, it was the first time so i babysit the charging the whole time

 

[saeckereier]

Re: Charging 18650 and Life Question.

No. When you connect 2 cells of different voltages in parallel (+ve to +ve and -ve to -ve), there is an instant flow of charge from the higher one to the lower, until they achieve balance. Effectively, the higher cell is charging up the lower cell.

This current flow can initially be at a very high rate indeed, but the voltage of the higher cell will quickly sag and the current will then settle down to a more reasonable rate, dropping all the time, with the cells eventually achieving full balance after ~15 minutes or so.

Li-Ion cells can tolerate high current in short bursts, but connecting 2 cells in parallel should not be attempted if the voltage difference between the cells is more than 0.5 volts.

Now that I didn't know, thanks for the enlightment. Disregard what I said

 

[mdocod]

Re: Charging 18650 and Life Question.

thanks, I was trying to charge 3 18650 LiPo pack which has exactly the same age and wear. charging them 1 by 1 just time consuming so decided to paralel charge them.

When in 1S3P configuration is that mean i can increase charging current by 3 folds?

your original post asks about standard li-ion (cobalt oxide) and LiFeP04 cells, now you have changed the subject to Lithium Polymer. As far as charging methods, lithium Polymer follows similar rules as Cobalt oxide cells. They do not tolerate overcharge well, and should be charged parallel with similar starting voltages, or individually, or with a balancing charger.... To answer the charging rate question, yes, for example, lets say you have a cell rated to be charged at 2 amp, and you wire 3 of these cells in parallel, you can now theoretically increase charging rate to 6 amps, (each cell will still be seeing about a 2 amp charge rate)...

 

[rizky_p]

Re: Charging 18650 and Life Question.

your original post asks about standard li-ion (cobalt oxide) and LiFeP04 cells, now you have changed the subject to Lithium Polymer. As far as charging methods, lithium Polymer follows similar rules as Cobalt oxide cells. They do not tolerate overcharge well, and should be charged parallel with similar starting voltages, or individually, or with a balancing charger.... To answer the charging rate question, yes, for example, lets say you have a cell rated to be charged at 2 amp, and you wire 3 of these cells in parallel, you can now theoretically increase charging rate to 6 amps, (each cell will still be seeing about a 2 amp charge rate)...

sorry i mean LiIon

 

[rizky_p]

Finally finished my 3x18650 lithium Ion Pack for My Son RC. Configuration 3S1P. I also add 3S balance connector for charging. Work nicely and charges easily and safely with hobby charger. I can monitor all cells voltage.



thanks