Charging 18650 batery via 2A USB wall charger.

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Hello,

i have a battery pack (6xx 18650 in pararell) whit output of 3.7V and a total capacity of 17400mAh(6x 2900) and i wish to make a charger from scratch. So far after reading a lot of documentation and CC/CV procedures when charging and came to a conclusion that i can make this thing relatively simply using my 2A 5V wall USB charger.

 

So i made a circuit that will do this:

 

First it connects the batteries directly to VCC output of wall charger. This will effectively put whole thing in a CC mode, since charger can only provide 2A(2.1A) and the batteries would pull a much higher current if the current would be available. All the time it is measuring the voltage on the batteries using a attiny and after the batteries voltage reaches 4.1V, it closes the VCC line feeding the batteries (using a mosfet/relay) and feed to batteries output of buck converter providing 4.2V whit 2A max output. It keeps it so until the current feeding batteries(it measures it whit a votlage drop on a low Ohm current sense resistor) drops below 5% of rated current. After, it disables any power going into batteries and just measures batteries voltage every 10 second until it falls under 3.3V and then starts charging again. It also constanlty measures temperature whit 3 temp sensors glued to pack on 3 different places whit thermal conductive tape and if any temperature exceeds threshold (currently set to 40°C) it closes any power line going to/from batteries and start flashing alarm LED.

 

Would this procedure be safe to the PCB itself and also the batteries?

 

Thanks for any help

 

EDIT: I realsied i can not charge battery directly from wal lcahrger so that is why now i will put in a BQ2057CSN a 4.2V/2A output Li-Ion charging IC whit cc/cv/conditioning modes to charge the batteries. Now i am just trying to figure out all the possible additional protections for battery that i can implenent.

Last Edited: Wed. May 16, 2018 - 07:45 AM
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Oof....

 

Image result for dynamite

 

Waiting to happen.

 

There is only one safe way to charge lithium and that's with a lithium charger. Because of mobile phones there are any number of lithium charger chips available. If you want to see what happens when you get this wrong (a bug in your circuit or software) then google "lithium explosion" on YouTube.

 

Lithium burns with a pretty red flame - but keep a bucket of sand handy because it's difficult to extinguish with foam/water alone.

 

I particularly love the crowd reaction in this: https://www.youtube.com/watch?v=...

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But the whole pack can be charged whit a SAFE total of 4.3A (1075mA/cell according to datasheet at 0.5C), so if i charge it whit 2.1A from wall socker it shouldnt burn. And when it reaches 4.2V(according to datasheet) i limit it whit CV mode and it goes on charging.

 

I just simulated same thing whit my bench power supply setting it to 5V/2.1A (it went into CC mode) and when the voltage raised to 4.2V, i changed bench supply to 4.2V/2.1A and it went into CV mode and then i waited until current dropped below 0.2A(50mA/cell according to datasheet). 

I was also logging each battery temperature the whole time and they have never risen to more then 27°C (ambient temperature was 25°C), while the whole battery pack was enclosed into a plexi glass box of 20x20cm, so it was harder for it to cool using the ambient temperature.

I realise that software bug or anything could result in fire inferno, but that is why i am using 4x temperature sensors that have option to encode a max temperature value and if any of the sensors reach it, it sets its ALARM pin low, which then disables the MOSFET powering the circuit. This in terms shuts down the entire PCB and it doesnt turn itself on again, until the power is applied again whit reset power connenctor, to open the MOSFET again and turn the PCB on.

It also turn the entire PCB off if the battery level drops below min threshold (currently set to 3.4V) to protect batteries from over depleting and has to be restarted by reset power connenctor. 

 

P.S. I tested whole idea whit LGDAS31865 4-pack, since i had 4x 18650 batteries lying around.

Last Edited: Tue. May 15, 2018 - 02:47 PM
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I could also add a separated analog circuit whit mosfet driven by a zener diode, so as soon as votlage on pack rises above 4.2V, the mosfet would close and drive any excess power over the 10W resistor until the voltage would fall below 4.2V and the msofet would open again?

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Make sure your liability insurance is current and you have enough coverage! 

 

 

Click Link: Get Free Stock: Retire early!

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ebay/amazon has plenty of chargers for <$8...why not spend your time making something fun, like a talking doorbell that says "my dog is hungry".

When in the dark remember-the future looks brighter than ever.

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Because i need PCB that charges the batetry pack up and after that outputs from battery pack 4x 2A via step-up from 3.7V to 5V. And also gives me indication if battery is under 10%, at 50% and at 100% power. And i could not find an existing pcb that would do that :D

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You could not find these:

https://www.aliexpress.com/af/USB-charger-pcb.html?SearchText=USB+charger+pcb&d=y&blanktest=0&origin=n&isViewCP=y&jump=afs

 

But I don't think I would trust these circuits much better than a homebrew one.

For homebrew you do not only have to make a circuit that "works", but als consider faiure modes. (short circuits, broken MOSfet's).

 

What is the price difference between a complete high powered power bank and loose LiPo + PCB + casing + hours ?

Big Clive on Youtube has done some reviews of these things.

Some he liked, others were garbage.

Paul van der Hoeven.
Bunch of old projects with AVR's:
http://www.hoevendesign.com

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I can not recommend designing and building a D IY lithium charger.   There are many sources of 4056-based lithium charger module boards on eBay for $0.50 to $0.80 each.  If you have six 18650 batteries, then use one on these module boards on each and every cell.   Get a 5-6 amp  regulated +5V power source: a second-hand PC power-supply works well and sells for about $5.   For a short period of time, an uncharged 18650 will draw about 900mA during its charging cycle that is controlled by a TP4056.  Most of the time, each cell will draw about 200-500 milliAmps during charging.

 

Don't fool around with lithium batteries!   Unlike NiCads they have the ability to release large amounts of energy when shorted.  This energy will heat up any material that is shorting the battery to the flame point of paper, cloth, and plastic.  18650s will explode like the firing of a 9mm handgun from overcharging by a +3V source.  The TP4056 charger ICs are designed not only to effectively charge the cell, but  they are also engineered to handle any unusual and unforseen consequence that might be overlooked by an individual building and using a DIY charger.  You do not want the legal responsibility of any fire or accident resulting from a DIY lithium battery charger!

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I could not find any whit total output of 6A(3x 2A) or 9A(3x3A) and at same time whit custom set-able detection of battery levels.

 

Well if i wanted to buy a premade powerbank, it would need to have 3x USB C output, each providing 2-3A of current, total capacity of at least 16Ah, being as smaaaaaal as possible since the whole thing is gonna be integrated into small housing, that is why i want it to be only batteries on its own, and the charging circuit to be integrated into an already existing motherboard - to save space.

 

Price difference between custom made battery pack with charger circuit+developing time and buying premade power bank is minute, but as i said before, i could not find a powerbank that would fit my needs. Also i need to make 240 of this powerbanks whit 6 batteries each so i at this volume of batteries, the price go reallly low :D

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The power supply charging the whole thing is a 5V/2.1A battery charger from samsung, not a 6Amp regulated power supply - i cant change this. 

And you think if i buy those 0.80€ pieces of crap PCBs from ebay and something goes wrong, the supplier will take any lega responsibilities? ;) There are government owned institutes that are test and certify these kind of electronic charges (among other electronic products) in my country and if i get my finished product successfully tested there, i am safe on a legal side of things. A custom designed Li-Ion charger that i will make myself, whit several safety features will be much safer that those from ebay whit 1 IC on and several peripheral components. I will be charging the battery whit purpose build IC for that, checking temperatures, having analog protection circuits to protect batteries from overcharging, over draining, over current, while each system being independent of the other one. 

 

In total:

-1x li-ion chargin cricuit BQ2057CSN 

-4x Temperature measurement, if over threshold the batteries disconnect

-Zener driven MOSFET to disconnect batteries if over 4.2V 

-whole pack bind together by rubber whit strech resistor lines in(similar princip to load cells) that detects even 0.5mm expansion of any battery in diameter and disconnects batteries

 

 

If you know of another method to protect batteries i am open for suggestion and thanks for advices :D

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Klemko wrote:

...since charger can only provide 2A(2.1A)...

 

Questions...

 

1) How do you know that?

2) What happens when you exceed that?

3) Do you know what 'rated output current' is?

#1 This forum helps those that help themselves

#2 All grounds are not created equal

#3 How have you proved that your chip is running at xxMHz?

#4 "If you think you need floating point to solve the problem then you don't understand the problem. If you really do need floating point then you have a problem you do not understand." - Heater's ex-boss

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Klemko wrote:
i have a battery pack (6xx 18650 in pararell) sic

The other freaks have focused on the charging aspect and explosions related. However by merely wiring 6 cells in parallel you've made a bomb right there. I don't know how these cells are wired in Tesla battery packs, but I think you need a fiar amount of electronics in a lithium battery pack.

 

Thinking to myself now - I've never seen a lithium battery pack without a built in charge controller.

 

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Link to charger:

https://www.samsung.com/us/mobile/mobile-accessories/phones/adaptive-fast-charging-wall-charger-detachable-microusb-usb-cable-white-ep-ta20jweusta/#specs

 

If i connect it to empty battery it wont work, since it outputs is 5V and around 2040-2090mA so it would damage the battery, so that is why now i will put in a BQ2057CSN a 4.2V/2A output Li-Ion charging IC whit cc/cv/conditioning modes to charge the batteries. Now i am just trying to figure out all the possible addtional protections for battery that i can implenent.

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Yes i agree so that is why now i will put on the motherboard of the device a BQ2057CSN 4.2V/2A Li-Ion charging IC whit cc/cv/conditioning modes to charge the batteries.

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Klemko wrote:

Link to charger:

 

That's not a charger. It's a 2A USB 5V wall-wart power supply. All the charging smarts will be in the phone. When connected to a Samsung it does something clever but other than that it's a PSU.

#1 This forum helps those that help themselves

#2 All grounds are not created equal

#3 How have you proved that your chip is running at xxMHz?

#4 "If you think you need floating point to solve the problem then you don't understand the problem. If you really do need floating point then you have a problem you do not understand." - Heater's ex-boss

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Ok thanks for correcting my terminology. But yea, it is a PSU whithou CC mode, so when it reaches max 2A output, it does not go into CC mode, but keep the output at 5V. That is why i am addind that Li-Ion charger IC.

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N.Winterbottom wrote:

I don't know how these cells are wired in Tesla battery packs, but I think you need a fiar amount of electronics in a lithium battery pack.

 

Thinking to myself now - I've never seen a lithium battery pack without a built in charge controller.

 

 

Cars run on 300+V so I would say the cells are in series and then in parallel via controller, just a guess though.

 

David

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LiIon battery packs usually have protection electronics, not a charge controller. Powerbanks have a charge controller as they charge off USB.

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Kartman wrote:

LiIon battery packs usually have protection electronics, not a charge controller. Powerbanks have a charge controller as they charge off USB.

When I made my statement I was thinking of Dell / Some HP Laptop packs and Bosch drill battery packs. These have external push button switches that display the level of charge with a bargraph of LEDs.

 

Thinking again - If you had a bunch of cells wired in series, in CC charge mode, the current would be identical through each cell, that's good, but how would you monitor each cell's voltage during the CC phase without an integrated controller (or multiple external connections) ?  Then in constant voltage mode on a 20V laptop or drill pack how to ensure each cell gets the correct terminal voltage ?

 

In parallel wired cell packs with protection electronics it gets even more complex because both CC & CV charge phases present problems when monitoring each individual cell.

 

 

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There are battery packs and there are battery packs! Yes, the battery drill packs usually have a charge controller in them. I put new cells in a cheapy Li Ion drill and was surprised at the amount of electronics in them. It was non-trivial and consisted of a few fets etc. These will probably have charge balancing electronics to ensure the multi-cell strings charge equally.

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I particularly love the crowd reaction in this: https://www.youtube.com/watch?v=...

OT:  Keep watching the video.  After that battery fire demo, there's an interlude before the next battery fire demo.  Incredible 3D-printed model aircraft.  I bet that's why Cliff had it to hand ;-) /OT

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