Lithium-ion battery protector or charger board? Both? - Page 1
Forum section: electronics / projects

author: romantronixlab
author_rank: Regular Contributor
timestamp: July 27, 2014, 02:47:48 pm
content: Hello againI am working on a little project modifying an electric screwdriver 3.6v, replacing Ni-cad with lithium (found right size) but I’m having a hard time finding information on the different devices to charge and protect the battery. Plan on using a TP4057 1A 5V but it does not say if it protects from under voltage. Also this uses 2 IC's taking up more space.Is a charging board the same as a protection board; is the protection board capable of controlling charging, or a hybrid of the two?What are the differences of the two?Probably I will end up etching my own design because of the limited size, but if I can use any of the two, or the two better.

author: mij59
author_rank: Frequent Contributor
timestamp: July 27, 2014, 06:10:59 pm
content: Hi,The TP4057 is only a battery charger.A battery protection circuit can e.g. monitor the battery voltage and current .The protection circuit will disconnect the battery from the load if the battery voltage get too low or the current gets too high.

author: romantronixlab
author_rank: Regular Contributor
timestamp: July 27, 2014, 06:46:54 pm
content: So it would be best to get a protection pcb to charge and discharge? Or would I still need the charger board.Hours long searching for information but nothing useful found.

author: microbug
author_rank: Frequent Contributor
timestamp: July 27, 2014, 09:54:38 pm
content: Find a protection PCB online (eBay, Deal Extreme, Aliexpress, battery websites e.g., orbtronic/all battery) for the protection side of things. Make sure the cut-off current is above the max current you expect to draw. Since you're replacing the batteries with lower internal resistance and higher voltage lithium ones, you'll want at least double the normal current. At a guess, 2.5A+.When the battery is functioning normally (i.e., not over 4.2V, not under 2.5V, not drawing more than protection pcb rated current), the protection PCB is effectively invisible. You can connect a charger board to the protected battery without problems. A very common charger board uses the TP4056 which runs off of a 5V source such as a USB port.

author: Zepnat
author_rank: Regular Contributor
timestamp: July 27, 2014, 10:33:35 pm
content: I wouldn't worry too much about a protection circuit if only you are using the screwdriver and are quite disciplined when you are using it, finding a protection board that will handle the ~20 amps or so needed by the motor won't be easy infact I've never seen one, most cut off around 5~6 amps.If you recharge as soon as the motor power starts to drop, the offload battery voltage will bounce back to a safe level.Running the motor till it stops however (like most people do) will permanently damage the battery. And good lithium batteries ain't cheap!Multiple batteries in series though must use a protection board.Personally I would use the TP4057 and maybe a protection board on the output on the charger I case the IC fails and tries to overcharge.

author: sleemanj
author_rank: Super Contributor
timestamp: July 27, 2014, 11:06:33 pm
content: Short answer: you need both.The charger manages charging, it follows a profile - soft start, constant current, constant voltage, shut down. It does not monitor the cell when discharging.The protection board sits monitoring the cell all the time until something goes into a very bad state (very low voltage, very high current) and then simply disconnects the cell, you don't really want the board to trigger as a matter of routine, it's a "fail safe".Usually you would have a protection circuit for each cell, if you're using 18650 cells for example the protection circuit simply sits on top of the cell -http://www.gearhack.com/myink/ViewPage.php?file=docs/Protecting%2018650%20Lithium%20Ion%20Battery- a "protected 18650 cell" simply has this circuit already installed under the plastic wrapping.LiPo packs (not the RC type) often have protection circuits built in also, usually quite visible on one edge of the cell.

author: romantronixlab
author_rank: Regular Contributor
timestamp: July 30, 2014, 10:30:47 am
content: I will be using 14500 so they fit inside the case, will the same charging profile as the 18650 applies?The driver used 3 1.2v ni-cad but Ill be using 2 lithium in parallel to increase the mah to 1800.I tested the max load current draw and it takes about 9 to 10 amps but that was holding it with pliers (no usual usage), and with normal load it draws about 3amps peak and leveled to 1.2 amps.I saw a charger board that fits nice inside the case but the protection board is whole new story. Will probably need to design one in eagle that have the charging portion in it. If I cannot find one already made that fits.Thanks for the reply guysThis is what i like about modding and electronics.

author: sleemanj
author_rank: Super Contributor
timestamp: July 30, 2014, 11:04:05 am
content: You can get boards that do both charge and protectThe charge profile is the same regardless cell size, but the maximum current you should charge at is related to the cell capacity, a typical rule-of-thumb is you would want to charge at something around 0.5C (half the capacity, if your battery is 1000mAh, 500mA max charge current), but see the datasheet for the specific cells if available.

author: Zepnat
author_rank: Regular Contributor
timestamp: July 30, 2014, 09:06:40 pm
content: Don't take this the wrong way but trying to get 10amps out of two 14500's is asking for trouble. A IMR 14500 can do about 3 amps but they are only about 600mah, which add up to the original 1200mah. Please just replace the ni-cd's they have much higher current capability and don't have the explosion and fire risk of lithiums.

author: sorin
author_rank: Frequent Contributor
timestamp: July 31, 2014, 06:25:19 am
content: You need LiFePO4 Batteries.

author: romantronixlab
author_rank: Regular Contributor
timestamp: August 01, 2014, 03:12:59 am
content: Quote from: Zepnat on July 30, 2014, 09:06:40 pmI got two 900 to make 1800mah. I know ni-cad's have more amperage per cell but it gets to me when they are drained with no use, and it at the time when i need it most.Quote from: sleemanj on July 30, 2014, 11:04:05 amWill order some of those to try it out.

author: NiHaoMike
author_rank: Super Contributor
timestamp: August 01, 2014, 04:34:57 am
content: Use low self discharge NiMH.

author: Zepnat
author_rank: Regular Contributor
timestamp: August 01, 2014, 10:27:30 am
content: Quote from: NiHaoMike on August 01, 2014, 04:34:57 am+1

author: romantronixlab
author_rank: Regular Contributor
timestamp: August 03, 2014, 12:59:50 pm
content: Quote from: Zepnat on August 01, 2014, 10:27:30 amNi-MH is a decent alternative but where is the Make part of things, I like to explore and design new things on my own. Of course why reinvent the wheel if this is already available on eBay or other places. But i like the excitement and the goal celebration at the end of a completed project. BTW I know very clear the dangers of playing around with lithium batteries seen enough YTube videos about it and have seen how loud and powerful they explode at my workplace. :-//Hence this post - how protect and circuits.Thank You all again for the opinions, suggestions and comments they are all welcome.