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I have a few questions about charging Lithium Ion Batteries aka a collection of cells...im learnin...lol

1) I am looking to setup 14x18650 cells to make a 51.8v module in series. I know I need its best to use a BMS (purchased). I also got a smart charger that is designed to charge 14s modules. Can I use both at the same time? Or will they interfere with each other?

2) The charger in question is 52v but it is also rated at 3A. Am I missing something. I understand that to charge a 14s you would basically do 4.2v x 14 = 58.8v. But I thought in this case you would only charge it at standard amps of in this case 2.2A / 2 = 1A? Wont 3 amps be way over?

This project is for learning mostly so I am not planning to use this in real "production" capacity.

Thank you for your assistance!

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  • \$\begingroup\$ Where is your charger spec link? seems like a misunderstanding ... e.g. This Charger is a very small electric bike charger for 52-volt battery (14s 18650 lithium ion) which charges to a maximum of 58.8 volts. So dont confuse 52V LiPo battery charger with ability to go to 58.8 and cutoff \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Mar 1 '18 at 1:52
  • \$\begingroup\$ Different 18650 cells have different charge rates. Some can be charged at 4A. So a 3A charge rate is not necessarily a problem for SOME cells. Check the specs for your cells. Normally a BMS is built into the battery pack. The BMS shouldn't interfere with charging unless something odd is happening. But normally there is a little bit of system engineering that goes into selecting and configuring a BMS and charger for a battery pack to make sure it all works correctly. \$\endgroup\$ – mkeith Mar 1 '18 at 6:17
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Q1) Can you use BMS and charger at the same time.

Well it is not clear what you mean by a smart charger. If it is a bulk charger (i.e. just two wires connecting to the battery's bulk voltage) then you for sure want to use the charger in series with the BMS. The BMS is what is going to open circuit the charging line when one of the cells reaches 4.2v.

If it is a balance charger, (i.e. in addition to the two bulk wires there are a bunch of small wires/balance leads also connecting the charger to the battery) well you can still charge it with the BMS on there. You will need redundant balance leads though, or partially disconnect the BMS. But I am betting you have just a regular bulk charger.

Q2. Charger specs.

The charger is likely speced for a 52v battery. If you test the output it will probably go up to 58.8 ish volts. That would just be the nominal rating most likely.

Regarding the current: If the charger is rated to deliver 3amps, and you are hooking it up to a pack that is 14s x 1p (one cell in parallel only) then you will but charging the cells too fast really. The cells might be able to take it (check the datasheet for max charging rate) but there is a direct relationship between rate of charge and rate of wear on the battery. If you charge that fast, even if your battery can take it without failing you can expect your batteries to wear out quicker.

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  • \$\begingroup\$ Hi thank y’all for your responses. The charger is supposed to support CC then CV to the end. Which is what worries me about using it with the BMS which apparently does the same thing. Here is the link to both the BMS and Charger. vruzend.com/product/52v-14s-battery-management-system-bms vruzend.com/product/52v-lithium-ion-battery-charger-3-amps I might just use 3p14s to ensure I run smoothly assuming this charger works. I asked on their forum if it will work together but didn’t a response yet... \$\endgroup\$ – Dogboyaa1 Mar 2 '18 at 2:52
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    \$\begingroup\$ BMS's do not do charge control. They react to various conditions as needed. But in the context of charging, the BMS would only act to prevent charging if the charger tried to charge the cells to too high of a voltage. So as long as the charger behaves itself, there should be no problem. \$\endgroup\$ – mkeith Mar 2 '18 at 4:59
  • \$\begingroup\$ Yeah the BMS has nothing to do with CC-CV. It just stops the charging if any one cell goes above some set value (4.2ish) It is important to use the BMS with the charger together. \$\endgroup\$ – thejun Mar 2 '18 at 5:03

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