Lithium ion charging balancer questions for 18650s

[Trancistor]

Hi - I am new to this forum, and thank you for reading my post.

I am getting one of those cheap eBay Lion balancer boards (about $9) from China, about 4 cm x 6 cm.

It is a 5S 12A balancer.  It also protects the cells.  Questions:

1)  Can I use this to balance 3S or 4S?

2)  When balancing 5S, the maximum voltage needed is I suppose 5 * 4.2 = 21 V.  Will this charge the cells to 4.2 V each? What happens if the power supply delivers 25 V constant voltage.  Will the board attenuate that?

3)  What happens if the power supply can only deliver 19 V?  19/5 = 3.8 V.  Will all five cells balance exactly at 3.8 V or will they be random with a total of 19 V?  I understand that the cells will not be fully charged. 

4)  When you say 4S3P, is that 4 series of 3P or 3 parallels of 4S?

http://www.ebay.com/itm/5-S-12A-18-5V-Lithium-ion-PCM-BMS-Battery-Protection-Board-LiMn2O4-Balance-New-/122199648617?hash=item1c73aaa969:g:JJoAAOSwal5YEbUr

Thanks!   

[fourtytwo42]

Welcome to the forum Could you please post a link to exactly what balancer board you are talking about (could be useful) ?

Hang on you already asked these exact questions before here https://www.eevblog.com/forum/beginners/lithium-ion-balancer-questions/msg1250668/?topicseen#msg1250668 and got lots of answers, so why are you reposting the same questions again somewhere else ?

[Trancistor]

Done ...

[Trancistor]

Hang on you already asked these exact questions before here https://www.eevblog.com/forum/beginners/lithium-ion-balancer-questions/msg1250668/?topicseen#msg1250668 and got lots of answers, so why are you reposting the same questions again somewhere else ?

Because the audience can be different.

BTW, I did not get very useful answers.  Only two of my 5 questions were answered in a half-hearted manner.

Also, the question is of interest to both groups.

[SMdude]

Hi - I am new to this forum, and thank you for reading my post.

I am getting one of those cheap eBay Lion balancer boards (about $9) from China, about 4 cm x 6 cm.

It is a 5S 12A balancer.  It also protects the cells.  Questions:

1)  Can I use this to balance 3S or 4S?

2)  When balancing 5S, the maximum voltage needed is I suppose 5 * 4.2 = 21 V.  Will this charge the cells to 4.2 V each? What happens if the power supply delivers 25 V constant voltage.  Will the board attenuate that?

3)  What happens if the power supply can only deliver 19 V?  19/5 = 3.8 V.  Will all five cells balance exactly at 3.8 V or will they be random with a total of 19 V?  I understand that the cells will not be fully charged. 

4)  When you say 4S3P, is that 4 series of 3P or 3 parallels of 4S?

http://www.ebay.com/itm/5-S-12A-18-5V-Lithium-ion-PCM-BMS-Battery-Protection-Board-LiMn2O4-Balance-New-/122199648617?hash=item1c73aaa969:g:JJoAAOSwal5YEbUr

Thanks!   

1. Don't think so, you would need a bms specific for the amount of cells you have in series.

2. yes 21v is absolute maximum that should be applied. The board will not attenuate overvoltage, that is the job of your li-ion charger.

3 yes, if less maximum voltage is delivered, all the cells should still be at equal voltages.

4. You are correct, 4 series of 3 Parallel.

I think it is best to use a dedicated li-ion charger, be it a module or complete charger unit. In theory, if you had a 21v 1A supply, it should charge at constant 1A current until it reaches 21v, but I would not encourage it or rely on it and think that you would be taking a big risk in doing so.

Now, where is the 5th question?? 

Cheers and be safe with lithium!

[Trancistor]

Thank you so much for your replies.  After about 10 replies and re-replies, you are the first to provide some valuable info in this regards.

1) I have seen some BMS allow lesser number of cells to be used with a higher# BMS, if they are wired properly to the BMS.  So I understand this is not a standard practice.

2) Since it is difficult to have a charger that can precisely supply 21 V CV, is there an easier way to accomplish this?  Such as a 4R resistor in series in the 25 V CV circuit, with the over-voltage protection circuitry shunting the cell?  Lot of heat and not very efficient, but should work?

3) The 5th question was deleted as I figured the answer for that.  Thanks.   

[SMdude]

There are some switching power supply modules on ebay that claim to be adjustable, but I have never tried one. I have always opted for the more dedicated solution.
There seems to be a total lack of 18.5v/21v li-ion chargers or charge modules, so I can see why you are asking the questions you are
Did find this, use at your own peril!!
http://www.ebay.com/itm/Intelligent-Smart-Charger-21V-2-5A-for-18V-18-5V-5S-Li-ion-LiPo-Battery-pack-EUT-/221213089325?hash=item338153de2d:g:vswAAMXQw8hRZ7zw

As for bms and lesser cell amounts, I think I have seen them, but have never experimented this deeply. I leave this up to those who know better(or at least they should!)

Whatever you use to charge with, I would recommend a switch mode charger/power supply over something that just shunts/burns up extra voltage.

Or design your own discreet charger to meet your needs. Or a power tool li-ion charger...

Disclaimer, I claim no responsibility for anything you may do!

[fourtytwo42]

I apologize for my earlier comment I understand now why you double posted
About your number of cells and ideal voltage, perhaps you could use a more standard number of cells allowing you to not only use an off the shelf BMS but perhaps more importantly charger THEN use an off the shelf buck converter (switching voltage reducer) to power your load with the lower voltage you obviously want, the latter would be in the order of 90% efficient so you would not loose much. At the same time you would know your cells were being properly looked after!
Can you say what your load is or what its voltage requirement is ?

[Inverted18650]

Hey mate. That board is made for a 5S unit only. To get your precise 21V, grab a little DC/DC adjustable buck module and trim the pot to get the Vout to what you want. $4 on eBay.

Are you charging individual cells that you have wired up or is this a battery you purchased? Are they Li-Po or the 18650's, etc?

[Trancistor]

Thanks for the advice.  That is a great idea and I have ordered one.  They even claim it to be LCCCCV.

Yes, they are individual 18650 cells.  I want to get up to 96S.  What is the right way to achieve this?

[SMdude]

 
96s? Holy smokes!
Whatever you do, don't accidentally touch + and - !
You making a rodent eliminator?? 

In all seriousness, Do you need to bump the voltage up that high from the battery source?
Could you use a boost converter of some sort or do you require high current at that voltage? And efficiency?
As for a right way, I think you are on your own here.

[Trancistor]

Boost converter?    - we are talking about e-drive here.  Such as 24 kWh storage and 40 kW power.

[SMdude]

Yeah, righto. That makes sense then!

Good luck with it!

[Inverted18650]

Are you asking what's the best way to get 96 cells wired up series; Like should you solder directly to the terminals or use a cell holder? Ive never gone above 14S so I'm excited to see your project.