Li-ion battery Charging - Page 1
Forum section: electronics / beginners

author: rc_mandar
author_rank: Newbie
timestamp: June 17, 2015, 10:06:08 pm
content: Hello eevblog fans,I am a kinda newbie to electronics. I mean I had been working/playing with electronics gadgets but not entirely with the components till a few months back.I wanted to have a powerbank but instead of buying i decided to make a diy build. I have been watching EEVblog channel and couple of others too. GreatScott is also a good channel. Anyway, i broke open a lenovo z580 laptop battery and got hold off Sanyo R1112 3.7V Li-ion batteries. Upon opening the battery pack i googled the label and found that the li-ion cells are 18650 size/type and are also of unprotected type.Now i would like to use the battery cells, however, the task in front is how to charge them.I have following options:1) to buy this charger:http://www.ebay.de/itm/EU-Digital-Ladegerat-fur-Li-ion-3-7v-Akkus-4x18650-Vander-Batterie-/351428563186?pt=LH_DefaultDomain_77&hash=item51d2c650f2(because cheap and will be available to me fastet)2) or to use a dc-dc adjustable converter (cheap chinese) to 4.12V or 4.2V from 20V IBM laptop powersupply3) or to make a voltage divider circuit to 4.2V and supply power to it from a cheap chinese 5V 1A wall adapter.I do not care for life or capacity of the salvaged Li-ion battery cells. I do care for the safety of the user.Please suggest solution.PS: I have 6 li-ion cells (all working), would be in 3S2P configuration in the power bank.

author: codeboy2k
author_rank: Super Contributor
timestamp: June 17, 2015, 10:42:25 pm
content: Just buy a charger. It's probably the quickest, cheapest and safest for you.Anything you cobble together DIY will be unsafe and inadequate-- you will not make a professional case, and you will be putting yourself at risk each time you try to use it (and batteries need to be charged many times).Most chargers have current limiting and heat sensors built in that make them much safer. Plus they cover the unsafe electronic parts in nice molded plastic cases, something you are not likely to do if you DIY it using oddball DC-DC convertors and wall warts from china.The one you linked to says it is a "smart" charger, so I am assuming (perhaps unwisely) that it has a microprocessor and current and temperature sensors built in and will not overcharge the battery.

author: hayatepilot
author_rank: Frequent Contributor
timestamp: June 17, 2015, 10:45:32 pm
content: If you want to use the cells in 3S2P configuration, I suggest you charge them also in that configuration.Otherwise you would have to take the pack appart every time for charging. You would need to have a battery holder for this to be practical.To charge the whole pack at once I would recommend a charger from the RC Hobby department such like this one:Turnigy Accucel 6Dave did a teardown on this:He was pretty pleased with the little thing.Another big advantage of those chargers is that they can charge about any battery type.There are also ones with integratet power supply to run directly from mains.If you're in a hurry you can also pick one up from your local hobby shop. Although not quite that cheap.Greetings

author: Whales
author_rank: Super Contributor
timestamp: June 17, 2015, 11:30:04 pm
content: Many chargers are poor in terms of safety. Don't assume they are safe just because they are being sold on the internet.There are whole communities withhorror storiesandguides to safe usage. I recommend you have a read around if you already have not -- I am not a conclusive source of safety information!Be aware of some of the common pitfalls, such as:Trusting your charger not to overcharge. Many don't have tolerances good enough and charge to 4.3V or higher. Sometimes the exact same model has variation between individual chargers so some customers have no problems whilst others do.Trusting your charger alone. Cells sometimes get too hot, chargers sometimes overcharge. Never charge your batteries unattendedThe batteries you have harvested are likely lithium cobalt (LiCo) cells ('lithium batteries' is general slang, but there are actually many types) which are common in 18650 laptop cells. The '3.7V' is an average term: you generally charge them to 4.2V and discharge them to around 2.8-3V, but being more conservative in how far your discharge them avoids them deteriorating as quickly.

author: rc_mandar
author_rank: Newbie
timestamp: June 18, 2015, 02:32:47 pm
content: Hello guys,thanks for wonderful replies.@hayatepilot: Yes, i immediately thought about it. There is a newer version of this charger. It is a nice all rounder. I had it years back but do not have it any more. But this project is not a big deal so want to do it the safe yet dirty way.I am sorry but can't resist, so for the sake of the argument can any body answer me for the following question?Please see the image and tell me what will be the current flowing to the battery. My answer is around 660mA depending on the internal resistance of the battery.

author: hayatepilot
author_rank: Frequent Contributor
timestamp: June 18, 2015, 05:07:43 pm
content: Why have you connected the resistors in parallel instead of in series?Parallel resistors don't limit the current in a circuit! So if you would connect this circuit to an empty low internal resistance cell, there would be a very high current flow. It could easily exceed 10amps!I=dU/RdU=Voltage Difference Charger - CellR=internal Resistance of the CellI would at least put a 1Ohm resistor in series with the cell to limit the current to about 1A.Or better you use a LiIon charging chip from the start instead of the LM2596.Greetings

author: rc_mandar
author_rank: Newbie
timestamp: June 18, 2015, 07:05:42 pm
content: Yeah, lame mistake on part.

author: Rick Law
author_rank: Super Contributor
timestamp: June 18, 2015, 11:17:27 pm
content: Quote from: codeboy2k on June 17, 2015, 10:42:25 pmI agree with with codeboy2k here. I have been charging my 18650's with home-brew solutions. But to make any of them easier for my family to use, I had to ditch the gator clips, jumpers, and cryptic messages on home-grown programs.Sizing this "User Interface Improvement" project, converting the home-grown is going to be expensive and the packaging is going to be crappy. More expensive than the better low-end chargers. I ended up purchasing a mid range charger.Thermo-cutoff is critical when you are charging batteries in an unknown state. I have not placed enough importance in that until my last salvage. Any of the 6 from my latest pack is "a fire waiting to happen" when it is charged in high-Amp and without thermo cutoff.Apart from thermo cutoff, these are nice features I would suggest you look for:1. Adjustable charge current2. Adjustable max charge voltage3. Adjustable charge saturation (what is defined as full)4. Settable time limit5. Logging: Logging is important so you can analyze the charging/discharging profile of the unknown-state cell.5. Discharge testing (how many mAH or WH can this cell hold)18650 has enough power to create a big problem when something goes horribly wrong. So, you need to respect the power and the danger. The cheap charger address the charging well when it goes right. They do not adequately address what if it goes wrong.