18650 battery pack questions - Page 1
Forum section: electronics / projects

author: kallisti5
author_rank: Contributor
timestamp: February 16, 2017, 03:02:58 pm
content: I've constructed a small battery pack as a test unit for an upcoming robot project.This is my first 18650 pack, so I thought I would ask the experts here to keep from blowing myself up.The documentation on the protection boards I purchased is a little... light.I have a bunch of the following:http://www.ebay.com/itm/3-cells-3s-Li-ion-Lithium-18650-14450-Battery-Input-Ouput-Protection-PCB-12-6V-/191902625285My normal 18650 charger (Turnigy Accucell 6) won't charge the pack due to the lack of balance wires.I assume that protection board will charge the pack properly when 12.6v is applied as well?Applying 12.6 volts results in the board jumping around from drawing ~1.4A to 0A every second or so.

author: kallisti5
author_rank: Contributor
timestamp: February 16, 2017, 03:05:01 pm
content: Initial voltage was 11.6v. After 5 minutes or so @ 12.6v the voltage is 11.7v. So I assume the pack is taking the charge properly?

author: capt bullshot
author_rank: Super Contributor
timestamp: February 16, 2017, 03:10:13 pm
content: No, the board won't charge the battery pack on it's own. It just protects the cells from over- and undervoltage and sometimes from overcurrent.You'll have to apply a current and voltage limited source (say about 1C for 1h charge).For now, any decent lab bench supply will do with correct voltage and current set (4,1V to 4.2V per cells, 0.5 to 1A per nomimal 1Ah cell capacity).Beware, this method works but isn't a proper charger that will protect you from burning cells.

author: kallisti5
author_rank: Contributor
timestamp: February 16, 2017, 03:15:28 pm
content: So there's the rub. I really can't use the protection circuit at all for charging then? The output of the protection board is 11.7v. Applying 4.2v @ 1A draws 0 current.So i'm going to need an additional set of wires attached to the batteries directly to charge + balance?Here's the datasheet on the control IC:http://datasheet.sii-ic.com/en/battery_protection/S8254A_E.pdf

author: Zbig
author_rank: Frequent Contributor
timestamp: February 16, 2017, 05:02:14 pm
content: It's good you've opted for protected cells but the protection is not there to make your life easier. It's your job to charge the pack properly. What's stopping you from adding the balance connector so you could balance-charge the pack with your Accucell-6? Balance connector just taps the individual cells' terminals.After re-reading your post I realized you're not talking about individual protected 18650's connected in series but rather you've built your own 3S pack using some existing protection board. In that case, I withdraw my comment until I figure out what the board you've got is really supposed to do.

author: anishkgt
author_rank: Frequent Contributor
timestamp: February 16, 2017, 05:14:27 pm
content: You need to balance these cells and the BMS has it. The board says 10A so you can draw about that much current. Anything above that the BMS will cutoff the load. Now the balance wires goes from the BMS to the balance charger like an I max or similar. Assuming those cells are connected in series, you need to set the charger at 12.6v and charge at 1A. Check the battery spec to know the nominal charge current. 1A is safe as 1A to the pack means 0.3A charge current per cell.Charge the pack with the lipo setting and cutoff at 4.1 per cell. Most chargers automatically selects charge voltage depending upon the balance port connection. You just need to set current rate.Sent from my iPhone using Tapatalk

author: kallisti5
author_rank: Contributor
timestamp: February 16, 2017, 05:23:34 pm
content: So after all of this I get the feeling:1. I need to add a set of 3s balance wires to the sense/balance terminals on the protection board2. I then take the 'main' 12v connection from the balance board and connect that to "generic rc li-ion 3s charger"3. Balance wires connected to my "generic rc li-ion 3s charger"So pretty much i'm just missing balance wires. I can use the 12v output of the protection board?Interesting the example implementations of this board show cells hooked up without any balancing wires like you're supposedto use the pack and never charge it :-|This all makes sense and kind of what I assumed. The big question was if I had to run a another set of "unprotected" 12v wiresfrom the pack in series to the charger... which would be pretty messy and kind of defeat the purpose of the balance board

author: anishkgt
author_rank: Frequent Contributor
timestamp: February 16, 2017, 05:30:48 pm
content: The pic is missing these balance wires.https://www.ebay.com/itm/182308941316. It will have 4 wires of such 3 will go to B1+ B2+ B3+ and the remains to negative terminal. The charge and discharge terminals are the same. Get lipo tested as wellhttps://www.ebay.com/itm/322204396570. Once all are soldered. Connect this tester and check the voltage of each cell.Sent from my iPhone using Tapatalk

author: anishkgt
author_rank: Frequent Contributor
timestamp: February 16, 2017, 05:33:34 pm
content: Quote from: kallisti5 on February 16, 2017, 05:23:34 pmNope nothing more needed. Just the balance wires. Don't ask the Chinese questions. Most of them would not know they just sell.Sent from my iPhone using Tapatalk