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Max charging current lithuim 3s6p

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jourylek

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First of all let me introduce myself, I'm an electrical engineering student in college. I've been working my whole life with electronics but this is my first experience with 18650 batteries. I've made my own 50W high power flashlight and it's working nice off of wall power. However, I want to make it portable, so I bought 2 laptop accu and made a 3s4p accu. I'm charging it with 1A, and if my calculations are correct it will take approximately 17 hours to charge my batteries.

Battery specs: 3s4p of 2700mAh lithium batteries

Charger specs: Imax b6

My question, in short, as far as I know it is safe to charge a single cell with 1A. However, my battery has 6 cells in parallel, so is it safe to charge it with 6A? What is the max current I can charge my batteries with?

once again in short can i charge dis battery pack safely whit 3 amps?
Kind regards,

Joury (I'm Dutch so excuse me for some grammar mistakes)
 

alec_t

Well-Known Member
Most Helpful Member
Welcome to ETO!
Are you aware of the hazards of charging lithium batteries?
I suggest you start by reading this.
Do your cells have their safety cut-outs attached?
How do you propose to balance the cells?
 

jourylek

New Member
yes iám aware of the hazards, i ve read the article before i came here, but it dindt answer my question . and i do balance charge my battery whit a balance charge. the cell that i have a ript out of 2 new laptop battrys (becaus its cheaper to buy that in a laptop accu that separaly) and i could trial and error but that why i ask it because whit this kind of stun i do not want to end up as the note 7.
 

alec_t

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jourylek

New Member
i dont want my battery to end up as a battry from the note 7 ( in dont want it to explode ) it was a bad joke srry:)
 

audioguru

Well-Known Member
Most Helpful Member
Your battery will explode or catch on fire if you do not charge it correctly. The voltage and current must be correct and the charger circuit must disconnect the charging when it detects a full charge.
An 18650 battery cell usually has a manufacturer's name and part number printed on it. Then lookup its datasheet where they recommend the charging current.

How is "3S4p" connected? 3 cells in series making a string then 4 of the strings in parallel? Then there are not 6 cells in parallel.
 

jourylek

New Member
o sorry my bad. i is a 3s6p battery pack. and if i think logily as 1 18650 can handle 1 amp of charge then 6 in parallel means 6 amp a bit too much. or did i calculate something wrong? is it safe to charge it whit 3 amps? i uploaded a file of my calculations
 

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audioguru

Well-Known Member
Most Helpful Member
We do not know your battery cells because you did not post its datasheet or its part number.
Who says the capacity of each cell is 2700mAh? Who says the battery is 10.5V because it varies from 3.2V per cell when low to 4.2V per cell when fully charged which for 3 cells in series is from 9.6V to 12.6V.

We do not know if your "converter" keeps the LED current constant as the battery voltage drops as it discharges so the length of time for one complete discharge is difficult to calculate.
 

spec

Well-Known Member
Most Helpful Member
Hy jourylek,

Welcome to ETO.

We do not have many members from The Netherlands. Which area are you from? If you put it next to 'Location' on your user page, it will display in the box at the left of your posts.

Could you give a sketch of your battery pack to clarify exactly what the arrangement is. Do you in fact have three batteries in series to make one stack and do you then have two stacks connected in parallel. There is a further bit of information that we need to clarify: are the individual batteries connected in parallel with their corresponding partners in the opposite stack.

Can you also confirm that ACCU means accumulator (rechargeable battery).

Here is a bit of information about Lithium Ion (LiIon) batteries and batteries in general.

(1) It is always far better to charge each battery cell individually (that way you can cater for each cell's individual needs.
(2) The worst arrangement is to charge in series
(3) Charging in parallel is not so bad.
(4) LiIon batteries are the easiest to charge out of all the battery types to charge and use (properly): Lead/Acid, Nickel/Cadmium, Nickel/Metal /Hydride, LiIon.
(5) There are dangers with LiIon which means that you have to charge and discharge them correctly.

Is it possible to configure the 18650 LiIon batteries so that they can be removed from the torch and charged individually (don't worry how this will be dome for the time being)?

spec
 

jourylek

New Member
Hy jourylek,

Welcome to ETO.

We do not have many members from The Netherlands. Which area are you from? If you put it next to 'Location' on your user page, it will display in the box at the left of your posts.

Could you give a sketch of your battery pack to clarify exactly what the arrangement is. Do you in fact have three batteries in series to make one stack and do you then have two stacks connected in parallel. There is a further bit of information that we need to clarify: are the individual batteries connected in parallel with their corresponding partners in the opposite stack.

Can you also confirm that ACCU means accumulator (rechargeable battery).

Here is a bit of information about Lithium Ion (LiIon) batteries and batteries in general.

(1) It is always far better to charge each battery cell individually (that way you can cater for each cell's individual needs.
(2) The worst arrangement is to charge in series
(3) Charging in parallel is not so bad.
(4) LiIon batteries are the easiest to charge out of all the battery types to charge and use (properly): Lead/Acid, Nickel/Cadmium, Nickel/Metal /Hydride, LiIon.
(5) There are dangers with LiIon which means that you have to charge and discharge them correctly.

Is it possible to configure the 18650 LiIon batteries so that they can be removed from the torch and charged individually (don't worry how this will be dome for the time being)?

spec
im from amsterdam.

her is a schematic of my battery pack
https://postimg.org/image/dlvtcr0cv/ (high res)
 

spec

Well-Known Member
Most Helpful Member
Hi jourylek,

Amsterdam= nice :)

Thanks for the diagram; that illustrates your battery pack well.

spec
 

jourylek

New Member
thank u, but i im correct in series u may not exceed the rated 1 amp. but in parallel i should be possible. but because it is 6 paralel that means 6 x 1amp= 6amp total but i think that to much i think that charging this battry whit 3 amps sould be fine.
because i want to take this with me sometimes whit out balance charger. as far i know it sould not be a problem to charge it without a balance charger. (for some short time) (https://goo.gl/E6Qgei) this charge but i need to be sure that my battery can handle 3 amp of charge. (i would like to better safe then sorry)
 

alec_t

Well-Known Member
Most Helpful Member
The problem with 6 parallel strings of 3 is that the strings will not have exactly the same characteristics; which means that they may not all draw the same current. This could result in one or more drawing excessive current if you use a 3A constant-current type of charger.
 

jourylek

New Member
The problem with 6 parallel strings of 3 is that the strings will not have exactly the same characteristics; which means that they may not all draw the same current. This could result in one or more drawing excessive current if you use a 3A constant-current type of charger.
oke but if i balacne charge them on 12,6 volts @ 3 amp then it sould be fine ?
 

spec

Well-Known Member
Most Helpful Member
The problem with 6 parallel strings of 3 is that the strings will not have exactly the same characteristics; which means that they may not all draw the same current. This could result in one or more drawing excessive current if you use a 3A constant-current type of charger.
This is true, but as the schematic shows, the batteries are not only connected as strings of three but also in parallel. This means that the only option you have is to balance charge at three levels of six parallel batteries.

Unless you go for fast charging, forced charging etc, and in the process reduce the life of the battery, the charging regime for LiIon batteries is very simple: charge to 4V and discharge to 3V. You can juggle with the figures to get different trade offs. And that is all there is to it. Of course you are wise to limit the current to a level specified on the battery data sheet. This is an area where parallel charging does have a disadvantage: you cannot, in theory, fast charge, because you cannot guarantee that the batteries will current share at all times. In practice it is not normally a problem because the internal resistance of the batteries tends to even the charging currents out.

And once a bank of parallel bank capacitors have settled into their environment there should not be any problems.

As a consequence, you can charge LiIon batteries in parallel quite successfully, although as I keep saying, it is far superior to charge each battery individually.

In the case of the six batteries in parallel at a first stab I guess that a maximum charging current of 6A would be OK for 18650 LiIon batteries.

In terms of safety:

(1) Keep away while charging and discharging or if the battery is hot.

(2) Never put your eyes near a hot or charging or discharging battery. In fact, never put your eyes near any battery at any time.

(3) Legislate for an explosion- make sure that if a battery explodes it does the minimum of damage and that the damage is acceptable.

This applies to any battery type and any charging method. It also applies equally to, so called, protected batteries.

spec
 
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audioguru

Well-Known Member
Most Helpful Member
www.batteryuniverrsity.com says that a normal Lithium battery cell that has its charging terminated when its voltage reaches 4.0V has its capacity at only 75% of its rated fully charged capacity. Charging to 4.20V per cell then regulating that voltage but continuing charging until the current drops low is a full charge giving full capacity but the charging time is longer.
 

spec

Well-Known Member
Most Helpful Member
www.batteryuniverrsity.com says that a normal Lithium battery cell that has its charging terminated when its voltage reaches 4.0V has its capacity at only 75% of its rated fully charged capacity. Charging to 4.20V per cell then regulating that voltage but continuing charging until the current drops low is a full charge giving full capacity but the charging time is longer.
Yes, fully agree AG. That is the trade off between shorter battery life and more complex charging versus longer battery life and simple charging. The later is adopted in many critical areas, like Tesla electric automobiles for example.

Conservative charge/discharge voltages also increase safety.

Taking an example of a 18650 LiIon battery with a nominal capacity of 3.5AH (the highest you can get as far as I know). This would reduce to 3.5 *0.75 = 2.63AH, which is quite a reduction as you imply. The 75% figure is only average though and, in practice, and depending on the exact battery type and manufacturer, the loss in capacity can vary.

spec
 
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