Questions about Li ion/ Li Po batteries - Page 1
Forum section: electronics / projects

author: bneo99
author_rank: Newbie
timestamp: December 30, 2013, 05:06:25 am
content: I was looking at a Lithium ion battery charger onhttp://www.ebay.com/itm/New-5V-Mini-USB-1A-Lithium-Battery-Charging-Board-Charger-Module-IN-4V-8V-/400353508118And i was planning to use it to charge my camera's battery which is a Panasonic Model : cga-s/106c Li-ion 3.6v 740mAh battery, but I'm afraid that I may destroy the battery due to a mistake. So I would like to ask a few questions about this battery....There is this Data and Temp pin on this battery..... how do you actually interface with these pins?Is the Temp pin connected to a 10k NTC Thermistor? or is it connected to a temperature sensor (such as Lm35/ Ds18B20)The original charger for the battery is rated 4.2v at 650mA and the charger connects to the battery temp pin for thermal protection....Any answers will be greatly appreciated....

author: peter.mitchell
author_rank: Super Contributor
timestamp: December 30, 2013, 06:47:00 am
content: I don't know why, but my instincts tells me that is a 4.1v maximum cell, so that charger won't do, because it has a fixed 4.2v charge voltage. If this isn't the case, please someone else chime in and correct me.If it isn't the case, and you do use this chip, i'd recommend a 0.5C charge rate, or thereabouts, small cells don't like high charge rates. That can be obtained by using a 3.3k~ resistor between PROG (6) and ground.At that charge rate, temperature monitoring isn't really needed, so you can ground the temp pin (1).

author: amyk
author_rank: Super Contributor
timestamp: December 30, 2013, 07:09:22 am
content: There are really only 2 voltages for lion chemistry depending on the electrode material , 3.2 (phosphate) and 3.6/3.7 (cobalt). The fully charged voltage for the former is 3.6V, and the latter is 4.2V. You likely have the latter type.The more important thing is the charge rate, charging at 740mAh battery at 1A is 1.35C which is too fast - manufacturers usually recommend ~0.6C for a regular charge and 1C for a fast charge. So do not exceed 740mA charge current, and keep it closer to ~400mA for a regular charge.

author: sleemanj
author_rank: Super Contributor
timestamp: December 30, 2013, 07:43:12 am
content: The board uses the (rather common for chinese charger boards) TP4056 single cell charger IC. Look up the datasheet for that IC and you'll find 2 things of usehttp://dlnmh9ip6v2uc.cloudfront.net/datasheets/Prototyping/TP4056.pdf1: information about setting the charge rate, as mentioned by a poster above you're going to want to modify it, you can locate the RProg on the board, remove it, and replace with an appropriate value (in addition to the table in the datasheet, 30k will get you around 50mA, and 20k around 70mA)2: information about the temperature sense, specifically that the TEMP pin of the chip should see voltage between 45% and 80% of the VCC (or ground to disable temperature sense), anything outside those ranges will shut down for over/under temp. So you'll have to look at the board to see how that TEMP pad is connected, my guess is that it's connected to the temp pin but that there is also a resistor from there to GND so it's disabled by default, and you'd need to connect your thermistor between VCC (which is probably brought out to IN+) and the temp pin to form the upper leg of a divider (with the on board pull-down as the lower leg). So the value of the NTC will be determined by that on-board pull-down.NB: I don't know what's going on with the TEMP section of the example application on that datasheet, looks wrong to me, but perhaps there is some standard temp-pin output of battery packs that they are trying to show.

author: RolfNoot
author_rank: Contributor
timestamp: December 03, 2015, 11:36:31 am
content: I'm sorry for replying this old topic but I was looking for the resistor values for the NTC circuit. This maybe helpful to others looking for the resistor values.According to the datasheet, the TEMP pin has to be between 45% and 80%. If we use 5V for supply, the voltages would be 2,25V and 4V.The datasheet mentions two resistors R1 (the pull up resistor to 5V) and R2 (the pull down resistor to GND). The NTC (R) is connected in parallel with R2. If we use a 10K NTC with a beta of 3477K the resistance for 0°C and 50°C would be 28.5K and 4.1K resp.Now we have two equations:R1 / (R2//4.1K) = 2.75V / 2.25VR1 / (R2//28.5K) = 1V / 4Vmaking right side 1:0.82 x (R1 / (R2//4.1K)) = 14 x (R1 / (R2//28.5K)) = 1substitute:0.82xR1 / (R2//4.1K)) = 4xR1 / (R2//28.5K) or4.89x(R2//4.1K) = R2//28.5Krewriting the parallel resistances:4.89x(4.1KxR2/(4.1K + R2)) = 28.5KxR2/(28.5K + R2) or20.05xR2x(28.5K + R2) = 28.5KxR2x(4.1K + R2) or28.5K + R2 = 1.42x(4.1K + R2) or28.5K - 5.82K = 0.42xR2 orR2 = 54K, round it to the available 56K resistorAnd we know:4 x (R1 / (R2//28.5K)) = 1 orR1 = 1/4 x (56K//28.5K) orR1 = 4.72KSo for protecting charging for lower temperatures than 0°C and higher than 50°C we should use a NTC of 10K with a beta of 3477K and R1 = 4K7 and R2 = 56K.Regards,Rolf

author: calistarh
author_rank: Newbie
timestamp: March 01, 2018, 05:37:27 pm
content: Awesome! Thank you very much for this. It is still relevant today.

author: mikerj
author_rank: Super Contributor
timestamp: March 01, 2018, 06:49:02 pm
content: Quote from: amyk on December 30, 2013, 07:09:22 amNot quite true, there are cobalt based cells with maximum voltages of 4.1v and also higher voltage cells that can be charged to 4.3v and even 4.35v.

author: Audioguru
author_rank: Super Contributor
timestamp: March 02, 2018, 12:07:18 am
content: The new Lithium batteries that can charge to 4.35V and take thousands of charges are called "Lithium Graphine". They are sold today for electric radio controlled airplanes, cars and drones.

author: amyk
author_rank: Super Contributor
timestamp: March 02, 2018, 12:28:41 pm
content: Quote from: mikerj on March 01, 2018, 06:49:02 pmNote the date... 4 years ago.Yes, I'm aware of the 4.3 and 4.35v cells now; but do you have any references for a 4.1v cell? I've never seen anything below 4.2 as the maximum for non-phosphate cells, although I know some systems charge them only to 4.1 to prolong cycle life.

author: mikerj
author_rank: Super Contributor
timestamp: March 05, 2018, 10:46:24 am
content: Quote from: amyk on March 02, 2018, 12:28:41 pmThe 4.1v cells tend to be older devices IME, usually marked as 3.6v nominal rather than 3.7v. This is why you can get charger ICs that cut off at 4.1v, e.g. BQ24203, MCP73826-4.1.