Li-ion battery protection/charging module  - Page 1
Forum section: electronics / projects

author: Asim
author_rank: Regular Contributor
timestamp: July 16, 2014, 09:37:51 pm
content: Hello guys,I bought this " PCB Charger for 4 Packs 3.7V Li-ion Li Lithium 18650 Recharge Battery" off ebayhttp://www.ebay.com/itm/Max-4-5A-PCB-Charger-for-4-Packs-3-7V-Li-ion-Li-Lithium-18650-Recharge-Battery-/261191600278?pt=LH_DefaultDomain_0&hash=item3cd03b8896.It has overcharging and discharging features. The main charge controller chip is Seiko S-8254A 3 or 4 cell lithium charger IC:http://datasheet.sii-ic.com/en/battery_protection/S8254A_E.pdfThe other chips are p-channel mosfets, Alpha Omega Semiconductor 4419shttp://www.aosmd.com/res/data_sheets/AO4419.pdfSO, as you can see from the ebay link, P+ and P- are used as the output or the charging points. My Question is: do I have to wait for the over discharge protection(2.4V) to kick in before being able to charge it or can I charge it while it is not in the over discharging protection?( I don't want to connect a power supply to charge it while it is giving me output voltage). I might be over thinking it,but better be safe than sorry.I read the datasheet trying to figure out this but no luckfeel free to ask me any question.Thanks in advance

author: Ton
author_rank: Regular Contributor
timestamp: July 16, 2014, 11:01:46 pm
content: You have bought a safety protection board for your battery, this is goodif you care well for your battery cells the protection board should never actual take any actions,If your want your battery cells to live long and prosperyou should take care that they are never charged higher than Vmax (typical 4.2Volt on a li ion type battery) minus some small safety/long life margin maybe 0.05V to 0.1Vthis give you a charger maximum voltage of number off cells * 4.1V as maximum voltage.far from the safety limit of number of cells * 4.35V. At this level some degrading have already started, but serious breakdowns are prevented.at discharge the same applies if you care for your cells you should not discharge them deeper than approximately 3.0V to 2.7V per cell, going all the way down to the safety limit of 2.4Volt means that degrading have started, but serious breakdown is prevented.anyway the energy left in a li ion cell when you have gone below approximately 2.8volt is very limited.as for charging, you can start a charging cycle as long as the cell voltage is lover than your maximum charge voltage minus some offset. So if you charge your cells to a voltage of 4.1V per cell, I would not restart the charger before the cell voltage is 4.0V or lower.Li ion don’t like being trickle charged, always charge them with Constant current until they reach final cell voltage and then keep them on Constant voltage until charge current have become 1/5 to 1/10 of the Constant current level.Hope this makes sense it was written in a hurryTon

author: Asim
author_rank: Regular Contributor
timestamp: July 16, 2014, 11:27:45 pm
content: If I understood correctly, it is safe to charge them when the batteries at 3.5V ( as an example) as long as the charging voltage is higher than 3.5V + margin ?Correct me if i am wrong

author: Ton
author_rank: Regular Contributor
timestamp: July 17, 2014, 12:40:10 am
content: LI Ion charging.example 4 cell. Panasonic NCR18650B 3.3Ah Li Ionhttp://industrial.panasonic.com/www-data/pdf2/ACI4000/ACI4000CE54.pdfMaximum voltage per Cell 4.2 => max battery pack voltage 4*(4.2-0.1)Volt = 16.4V for long life (maximum capacity would be at 16.8V)Max charging current from Data sheet 0.5C => 0.5 * 3.3 = 1.65ASo a charger could be a laboratory PSU where you set up the current limit to 1.65A, and the voltage to 16.4V - I would recommend a li ion charger since it would handle everything in the charging if setup correctly including proper charge termination.a charge cycle could then be: check battery package voltage and if lower than 4* 4.0V=16V then charging is ok. but will only add a few % charge.Your example of 3.5V per cell => 14 Volt would be a battery pack discharged around 50 to 60%if you connect the battery package discharged to 14Volt to the lab PSU setup as described above, you would measure something in this region.after connection :Vbat 14.4V, Ibattery 1.65A => charging in CC (Constant Current mode) adding energy to the battery very fast.The voltage rise on Vbat is based on internal resistance and "chemical reaction" resistance and it varies with different batteries.after 30 to 45 minutesVbat vould reach 16.4V and PSU would change to CV (Constant Voltage mode) and the current would slowly decrease to ~ 0Ain this mode the addition of energy slows down, as the current becomes lower.after 75 to 90 minutes the current would have reduced to around 0.165A and the Battery Pack would be fully chargedLI ion cells can be topped up, but they don’t like being kept on a charger that charges constant, but if we want to we can re charge when batterypack voltage has gone a bit down.for further information have a look in this booklet from Panasonic regarding use of Li Ion batteries.http://industrial.panasonic.com/www-data/pdf/ACI4000/ACI4000PE5.pdfand now it is 02:30 local time and it is a work day tomorrow so I am off nowBR Ton

author: Asim
author_rank: Regular Contributor
timestamp: July 17, 2014, 03:46:56 am
content: Thank you ton for this lengthy explanation, you cleared some points.

author: HKJ
author_rank: Super Contributor
timestamp: July 17, 2014, 06:43:25 am
content: It looks like the protection PCB are missing a balancing circuit (They usual are). This means that the batteries will get out of balance after some time and the protection will disable the pack.Use a hobby charge to balance the cells, maybe once a year, will prevent this.

author: Asim
author_rank: Regular Contributor
timestamp: July 17, 2014, 07:55:39 am
content: Oh, that's true. I will get a one with balancing built into it. For charging the circuit I was thinking of this itemhttp://m.ebay.com/itm/320860505997?nav=SEARCHDo anyone see a problem with it ?

author: Ton
author_rank: Regular Contributor
timestamp: July 20, 2014, 08:31:35 am
content: That charger should be fine for most 18650 cells.I would check the 16.8 Volt, if a few 100mV lower no problem, but if just a little higher then you are pushing your cells beyond max voltage. and there by reducing battery life/charge cyclesand Yes battery balancing would be best.Br Ton