Author Topic: Protecting 2 18650 Li-ion batteries.  (Read 1371 times)

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Offline VEGETA

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Protecting 2 18650 Li-ion batteries.
« on: September 30, 2016, 09:07:09 am »
Hi

I've been searching of means to protect 2 series 18650 batteries (assume unprotected and not genuine) and I came up with this:

Instead of an IC to protect the 2 of them together, I thought of protecting each one of them individually using this IC: http://www.diodes.com/_files/datasheets/AP9211.pdf

This IC has the 2 mosfets inside it, so will it work this way? I tried to mimic the status of having 2 protected cells in series. Here is a schematic photo:



What will happen if the user put 2 protected cells with this circuit?

thanks
 

Offline amyk

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Re: Protecting 2 18650 Li-ion batteries.
« Reply #1 on: September 30, 2016, 11:14:37 am »
Yes, protected cells will work the same as normal cells within the protection limits. They may appear to have a slightly higher internal resistance due to the MOSFETs within the protection.
 
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Offline VEGETA

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Re: Protecting 2 18650 Li-ion batteries.
« Reply #2 on: September 30, 2016, 02:24:02 pm »
So my circuit is correct if the 2 cells put in series?

My concern is that the protection IC is made for one cell... so maybe the voltages will affect it. Like having 0-4v for first cell while the 2nd one is 4-8v. I wonder if this is normal and won't make a problem.

The datasheet I guess says "Battery positive" and "Battery negative" so voltage doesn't matter here. My point is having a +4v voltage difference between VDD and VSS instead of a true 0v on VSS. Is this gonna work fine?
 

Offline VEGETA

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Re: Protecting 2 18650 Li-ion batteries.
« Reply #3 on: October 06, 2016, 11:03:09 pm »
Will my circuit work for non-protected cells? 2 in series?
 

Offline VEGETA

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Re: Protecting 2 18650 Li-ion batteries.
« Reply #4 on: February 18, 2017, 07:01:14 pm »
I've thought about this and I finally settled to use 4 Li-ion batteries! 2 in series and 2 in parallel for increased current because it is important for me. The pack's total voltage is 8.4v maximum, so will this individual protection technique works fine or should I make a 8.4v over-voltage protection for the whole pack?

If protecting the whole pack is safe I will get it... but what IC? I couldn't find a suitable IC for this. I am glad to take help.
 


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