MAX amp for charging LI-ION???

Hi

I just bought this 36V Samsung 29E battery, size 14.5 AH.
http://www.eclipsebikes.com/145ah-lithium-frame-battery-samsung-cells-p-1119.html

I want a new battery charger that can charge it FAST up to 80% == 40.05V


What is the max charge current that I can charge this with, up to 80%, without damaging the battery?
I see the following official specs:
Charging Voltage: 4.20 ± 0.05 V
Charging Current: Standard charge: 1,375mA
Max. Charge Current: 2750mA (not for cyclelife)
http://www.candlepowerforums.com/vb/showthread.php?384132-Test-Review-of-Samsung-INR18650-29E-2900mAh-%28Blue%29


How should I understand the difference between standard and max and (not for cyclelife)?
How many amps? Is it 2-3-4-5-6-7-8-10 amps???


My own guess is:
4,2V/1,375 = 3 ----- 14,5A/3,0 = 4,8Amps for standard charge
4,2V/2,750 = 1,5 --- 14,5A/1,5 = 9,7Amps for maximum charge

Is this correct and how often can I use 9,7Amps??? Should I choose a 4,5 Amp charger instead to be safe?


Above 80% I use a slow 2amp 42V charger up to 100% charge.
I only use this 100% charger once or twice a month to balance out the individual battery cells.


Sincerely yours
Duncan

DuncanDK said:

I want a new battery charger that can charge it FAST up to 80% == 40.05V

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Cycle Satiator from ebikes.ca would let you charge it however you want to, up to 8A max current. You can create profiles for various ways you wish to charge it, including your 80% and 100%, and you switch between them in an easy menu.

You can also create fast and slow charge profiles, or jsut about anything else you'd liek to do with it (and not just for this battery....).

How should I understand the difference between standard and max and (not for cyclelife)?

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Standard means if you want to get the expected / rated number of cycles out of the cells, don't exceed that charge current.

Max means the highest current the cell is rated to take, and the "not for cyclelife" probably means that if you do that, you shorten the lifespan (number of times you can charge them back up, and eventually the capacity you get out of them, over time).

How many amps? Is it 2-3-4-5-6-7-8-10 amps???

Click to expand...

It states that already in the specs you quoted, for the cells.

4,2V/1,375 = 3 ----- 14,5A/3,0 = 4,8Amps for standard charge
4,2V/2,750 = 1,5 --- 14,5A/1,5 = 9,7Amps for maximum charge

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I don't know what that math is supposed to mean. Why are you dividing voltage by current? I don't know of any useful number (for what you're trying to do) that you can get that way. It definitely doesn't give you amps....

If you want to know what a complete pack of cells can take for current, you multiply the number of paralleled cells by the current the specs for the cell gives you.

Is this correct and how often can I use 9,7Amps??? Should I choose a 4,5 Amp charger instead to be safe?

Click to expand...

I don't have any idea what the actual numbers you can use are, but I would recommend not using anything higher than whatever the "standard" rate turns out to be.

It appears the max charge current is 2.75A. That's a little less than 1C. Normal charge current is ~0.4C, 1.375A. It's all in the specs as you posted, so I don't really understand what you don't understand. Your pack is 14.5ah so a max charge would be about 13A, while a normal charge would be 5.8A.
http://lygte-info.dk/review/batteries2012/Samsung INR18650-29E 2900mAh (Blue) UK.html

What will actually limit your amps charging, is more likely to be the max your bms is built to handle.

Reasonable to assume it can take 5 amps. Some bms are rated 8 amps. However, they recommend only 2 amps. Likely this is to extend cell life as much as possible. They give no max amps for the bms in the spec, so anything above 2 amps is a pure guess that it can take it.

The faster you charge, the less long you expect the cells to last.

One cell can take 1375 milliamps of charge current. That means one cell can take 1.375 amps. five cells parallel connected can then take 6.875 amps, for the lower rate of charge spec.

So a 5-8 amps charger could work. I wouldn't go more. Ideally, find out more about the bms used.

Thank you very much for your replys.
They helped me understand how to calculate the max AMP

you don't need to calculate the max amps. they are WRITTEN in the posted info
and as much appealing fast charging is: the faster you charge the shorter is your battery life. this may be an issue for you, or it may not. i use my bike for fun only, so i ride it once or twice a month. even charging at full allowed current will not happen often enough to make my battery last significantly shorter.
if you use your bike for going to work on a daily base i would recommend charging as slow as possible. you get home in the evening. connect the charger and let it charge over night.
i charge my bike to storage voltage after each ride and just do a fast top off with 1-2C before i leave. this takes 15-20min and is the time to put on bike cloth and stuff.

Dear Wesnewell, dogman dan and Izeman

You three come to three different answers to my question. It confuses me a little.

Wesnewell : 5,8 amps (is that 1,375*4,2??) How do you arrive at this number?
Dogman dan: 6,875 (That is 5 cells in parallel * 1,375 each)
Izeman : You do not mention a specific number. Do you mean 2 amps? Thereby referring to the "Standard charge"-number in the add for the battery?


My reason for asking is that I see 2 amp mentioned in the add as standard charge. But I think that it refers to the charger that comes with the battery and is not the standard charge current of the 14,5ah battery.

However, I have heard two other "sayings" when charging your 36V battery to only 80% (40,5V):
1) You can charge LI-ION batteries at half the amps of the AH of the entire battery. In this case 14,5/2= 7,25 amps
2) Each cell has a standard max, which can be multiplied by the number of cells in parallel. In this case 1,375a*5cells parallel = 6,875 as Dogman dan

Thats is pretty close to each other, - is it just a coincedence?. Wesnewell how do you get to your number? And Izeman how did you get to yours?

I am told that from 80%(40.5V) to 100%(42,0V) a lower current should be used in order to ease the BMS' task of levelling out charge voltage among series and cells in parallel. Is there any truth to this?

I estimated it thinking it was a 4p pack. I never looked at the the battery link.
It's a 10s5p pack with a bms. For sure the max charge current will be limited by the bms as dogman stated. Standard charge rate is 2A. They don't list max charge rate or I missed it. 5 x 1.375 = 6.875A normal charge rate for 5p. 5 x 2.75 = 13.75A max charge rate for 5p. My guess would be the bms supports a 5A max and it may be less than that, so what the batteries can take is irrelevant. The little 2A charger that comes with it will take ~7 hours to charge an empty pack. 14.5ah divided by 2.

Dogman dan made the calculation for you. Your battery is 14.5Ah with cells that have 2.9Ah capacity each. So it's 5 of them in parallel. 5 x 2.9 = 14.5. Each cell has a standard charge current of 1.375A. 5 x 1.375 = 6.875A. But the BMS may be the limiting factor.

All right, thanks all!!!

btw: if you read carefully those cells are rate 2.850 at 0.2C charge and discharge. so if you pull more than 0.2 x 2.850 = 570mA or 2.8A from your whole pack you will probably not get 2.850mAh per cell (or 14.5Ah from the pack).
they are rated for a maximum charge rate of 2.75A, or 13.75A for the pack. but this will shorten life. if you want to make the pack live as long as possible charge at 14.5 x 0.2 = 3A. so a full charge from completely empty to completely full will take around 5h.
for super fast charging there are other cells. not those. you will not be able to fully charge this pack in less than an hour without charging out of it's specification.
i hope this does not confuse more than it did help

Cells can take 1C, but charging connector will likely burn at more than 2 A.