18650 battery's float voltage setting

DConlyGuy · December 2016

i am making 2 4p4s 16 volt battery's using the 18650 cells they are the 3.7 volt variety. my charge controller will charge at 16 plus volts and
it can limit how much amps it can put out too. im know full charge on the battery would be 16.8, but thinking of making it 16.4 or maybe even 16 volts . i can set the bulk and absorb to those voltages, but i know these cells dont like floated or trickled charged, so i was wandering on the float voltage to set is low so it never comes on might work? another thing is amp setting, these cells are averaging 2k mah so what amps setting on controller should i use to safely charge them ?

mvas · December 2016

RE: Charge Amps
The "Bulk Charge Amps" is usually between 0.5C to 1.0C.
Follow the mfr specs.

RE: Float
Correct, it is better to not float at 16.8v
Let the voltage drop and the trigger a recharge

RE: Max Voltage
Yes, lowering the max voltage will significantly increase total cycles, with slightly lower capacity ...
16.4 Volts vs 16.8 Volts could produce twice the cycles @ ~92% capacity
16.2 Volts vs 16.8 Volts could produce triple the cycles @ ~86% capacity
16.0 Volts vs 16.8 Volts could produce quadruple the cycles @ ~75% capacity

RE: Recharge Modes
Mode 1: Bulk Charge to 16.8v, then STOP. Wait for voltage to drop
Mode 2: Bulk Charge to 16.8v, then Absorb Charge until Amps < 3% then STOP. Wait for voltage to drop

http://http//batteryuniversity.com/learn/article/charging_lithium_ion_batteries
http://dolgin.net/Charging%20Lithium-Ion%20Batteries.html

Do not over-charge.
Do not under-charge
Follow mfr specs.

DConlyGuy · December 2016

thanks for the info so far, but here where i dont understand the math, ill have 32 cells total to start with and they will hopefully avg 2k mah each (dont have them yet) this is where i dont under stand how many amps to charge them all at at same time

mike95490 · December 2016

invest in a smoke alarm and keep exit routes clear.
String a whole bunch of batteries together, no BMS, no Binning of Cells to match them up, you will have trouble.

BB. · December 2016

Just a generic warning about any small lithium rechargeable battery:

https://www.youtube.com/watch?v=ZTzEHsJVZhA

-Bill

PNjunction · December 2016

DConlyGuy - thank you for identifying your cells as the 3.7v lithiums, which are far different from 3.2v nominal LiFeP04.

The catch-22 about doing lithium based projects, is that if you have to ask, you are unsafe. And with the limited info provided, you definitely are already in unsafe territory by thinking you just have to tack these things together, and set your charge controller voltage and be done with it.

So here are some more questions you need to know before you get started:

1) How are you going to handle temperature-compensation? (trick question)
2) What is your method of proving the all the cells have nearly identical capacity and internal resistance before assembly? How good are you at spotting fakes, or do you have a known good supplier?
3) Are you aware that these cells only have 300-500 cycles, and that a far safer but mech less energy-dense chemistry, like lead-acid AGM has similar cycle life?
4) Does your application actually demand this kind of energy-density? What voltage is your application actually going to use?
5) How much current does your application pull? - are you going to use "protected" or UNprotected cells?
6) What are your plans for over-charge and over-discharge? Similarly, what are you going to be doing in regards to balance?
7) What is your method of paralleling these 2K cells together? Soldering iron? Tack welds? Loose-fitting holders?
8) Have you give thought to switching lithium chemistry to LiFeP04, which is 3.2v nominal, and cutting your cell count down by only using 4 or 5 cells, like Headway's? Easier to charge with solar too by switching to the lower-voltage LFP chemistry.

So what exactly is your application with these cells? Maybe we can dissuade you from becoming a danger to yourself and others.

mvas · December 2016

DConlyGuy said:

thanks for the info so far, but here where i dont understand the math, ill have 32 cells total to start with and they will hopefully avg 2k mah each (dont have them yet) this is where i dont under stand how many amps to charge them all at at same time

I gave you the answer here ...
================
RE: Charge Amps
The "Bulk Charge Amps" is usually between 0.5C to 1.0C.
Follow the mfr specs.
================

If you do not understand the Li-Ion Charging Profile or the math, then you should not be charging Li-Ion batteries.
You must follow the manufacturers charging specifications.
Please provide the URL to the manufacturers charging specifications.

DConlyGuy · December 2016

mvas on the math i should of said how to figure the amp hours of the 32 battery's in the 4s4p configuration so i could get the right amp setting right

bill von novak · December 2016

DConlyGuy said:

mvas on the math i should of said how to figure the amp hours of the 32 battery's in the 4s4p configuration so i could get the right amp setting right

32 batteries cannot be connected in 4s4p. That would be 16 batteries. You do not want to charge any faster than 1C; .5C is a lot safer.

If you don't even understand what that means, you should NOT be trying to charge li-ion batteries. If you want to learn there are plenty of courses out there. Batteryuniversity.com is a good place to start.

DConlyGuy · December 2016

you are right bill i cant seem to ask the right questions the right way the 32 battery's will be two 4s4p battery's

PNjunction · December 2016

In addition to Battery U., there is also CPF (Candlepowerforum), BLF (Budgetlightforum), and of course EndlessSphere for the ebike crowd.

You'll get a similar grilling from them asking you to provide more details, such as what is your actual application, to be safe.

Lithium battery projects, from a single-cell flashlight, your own unknown 32-cell application, to that of a Tesla, requires a *SYSTEMS* approach, where more than just a single spec is involved to be safe and successful.

Answering any one of the questions I posed above (in case you missed it), will help identify if you are making an unsafe toy, or have a real interest in a working system.

DConlyGuy · December 2016

thanks bill von novak on the Batteryuniversity page half way down the 1st page they showed a picture of how to do ah. it amazing how a picture really does say a thousand words

mike95490 · January 2017

mike95490 said:

invest in a smoke alarm and keep exit routes clear.
String a whole bunch of batteries together, no BMS, no Binning of Cells to match them up, you will have trouble.

So this is all I have to write, and it gets me flagged for abuse ? Flag me for being snarky , but this is not abuse, unless you went to college and had "safe zones" to talk in.

I'm glad I don't live within your blast radius (when it goes up).

Just trying to get your attention that you are into dangerous stuff, and while you are asking some good questions, you have no concept of the other questions you need to be asking. And I can't ask them for you, because you don't give straight info about what you are doing or the source of the cells, but hey, go for it. Post your pics at the end.

18650 battery's float voltage setting

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