Charging Li-Ion batteries without disconnecting the circuit - Page 1
Forum section: electronics / beginners

author: Sesam
author_rank: Newbie
timestamp: March 06, 2016, 02:08:43 am
content: So I am currently trying to make a little Raspberry Pi robot and since I will also use a Xbox Kinect I assumed that 4 Li-Ion batteries in series would be the best way to go for such a project!Now my question is whether there is a simple way to charge the batteries without disconnecting them from the circuit and also provide power from the socket to the Raspberry Pi at the same time, so I don't have to turn the RPi off?I was researching this today and found out that I should use a 4S Li-ion Lithium Battery 18650 Charger Protection Board (http://www.ebay.com/itm/4S-Li-ion-Lithium-Battery-18650-Charger-Protection-Board-14-4-14-8-16-8V-30A-/331659239679). If I use this protection board do I still have to use a constant current device for charging?I also thought that I should use a ORing Diode to switch flawlessly between the battery and the power supply. Is my idea right?Thank you in advance,SesamP.S. Sorry for all this questions but I am just really inexperienced with this kind of stuff and I don't won't to blow it all up

author: Alex Trofimov
author_rank: Contributor
timestamp: March 06, 2016, 10:06:02 am
content: Dave did a video on li ion charging. I think, it contains all the answers to your questions. :-)http://youtube.com/watch?v=A6mKd5_-abk

author: Kilrah
author_rank: Unknown
timestamp: March 06, 2016, 10:11:42 am
content: Quote from: Sesam on March 06, 2016, 02:08:43 amYes, you still need a CC/CV charger. This is only a "last resort protection" that will disconnect the battery if something is wrong. It doesn't even balances the cells, it would only cut if one is reaching its safe voltage.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: March 06, 2016, 10:17:53 am
content: If your load draws a reasonably constant current it's fairly simple as you just need to add the load current to the charge current, and make sure you get an accurate voltage sense to avoid load current affecting the sense voltage ( i.e. star connected at the battery)If load current is somewhat variable it gets more complicated.

author: Sesam
author_rank: Newbie
timestamp: March 06, 2016, 05:16:45 pm
content: Thanks for all your replies!:)I've looked into the video and gladly I now understand the charging process of the Li-Ion battery!:)Unluckily I cannot assume that my project has a constant current draw!I've attached a version of the circuit which should be able to charge the batteries!To avoid having a constant current source I decided to use those charging and protection circuits:http://www.dx.com/p/tp4056-4-2w-1-2a-5v-lithium-battery-charging-discharging-protection-module-w-micro-usb-blue-397213For the voltage regulators I thought about using :http://www.dx.com/p/dc-3-35v-to-1-25-30v-converter-auto-step-up-step-down-solar-power-supply-module-for-arduino-147356orhttp://www.dx.com/p/mini-dc-dc-voltage-stabilizer-regulator-module-red-126106(I am not sure where the difference is!)The input Voltage would have to be around 17V I assumed.Since this is my first schematic I would love someone with experience to look over it! (Thank you in advance!:) )One thing I am not sure about is whether I have to disconnect the charging circuits from each other or not during the charging process; and if "yes" would relais be a viable option!

author: Kilrah
author_rank: Unknown
timestamp: March 06, 2016, 05:21:37 pm
content: You can't chain those single-cell chargers, you'd make a nice short circuit.You really need a single, 4-cell charger circuit and a balancing circuit (if not integrated in the charger).

author: Sesam
author_rank: Newbie
timestamp: March 06, 2016, 06:08:00 pm
content: Thanks for the fast reply!:)That's unfortunate!:/I wasn't able to find a of-the-shelf board for this purpose, but I read that one can charge them in parallel easier!So I have drawn another circuit which basically switches the batteries from series to parallel whenever the power source is connected with the help of relais.The only problem I have is that I will have to switch the Vin's in a specific order to prevent a shortcut, being Vin1, then Vin1, then Vin3 and last Vin2 (Using Capacitors). Is that right?I also schouldn't have to worry about balancing if I charge them in parallel if I change the charging circuit to charge them with 2C, right?

author: LordHexahedron
author_rank: Contributor
timestamp: March 06, 2016, 07:18:59 pm
content: Quote from: Alex Trofimov on March 06, 2016, 10:06:02 amthat link isn't working (you put a space in the url, between the ? and v=... why the url bbcode anyway? you just wrote the url in the name field anyway, thus defeating the purpose of the BBCode in the first place).but this one is:EEVblog #176 - Lithium Ion/Polymer Battery Charging Tutorial