DIY Li-ion from Toshiba Battery Pack

[nicksydney]

Hi,

Got a TOSHIBA battery pack today on discount for $1 and thought of using it for my son's Nexus 9 tablet battery pack. I've googled around and found info about the battery

https://detail.1688.com/offer/525378356188.html
http://www.sourcingelectricals.com/SANYO-UF404251S-1020mAh-Lithium-ion-Battery-10185652/

According to the website the battery is 3.7v 1020mAh. I have 2 questions

(1) From my basic calculation since the Nexus 9 will need 5V (USB) so I should configure the battery as shown in the diagram picture I've attached. Using series + parallel config I will be able to get 7.4v which will need DC step down (http://www.ebay.com.au/itm/DC-DC-Buck-Step-Down-Converter-Module-LM2596-Power-Supply-Output-1-25V-35V-AU-/262638807506) to step it down to 5V what I'm doing is correct ?

(2) The second is recharging the batteries. Can I use this kind of board http://www.ebay.com.au/itm/NEW-Li-ion-Lithium-Battery-Charger-Module-Li-LED-Board-5V-1A-Mini-USB-Board-/282158390422 and hook up each of the battery to each of this kind of rechargeable board for charging them ?

Thanks for the help

Cheers

[sleemanj]

hook up each of the battery to each of this kind of rechargeable board for charging them ?

No.

Not unless the cells are disconnected from each other while charging.  The charger board is not isolated.

The easier method would be to put all the cells in parallel and boost to 5v instead of bucking to 5v.  Then you can use ONE of those charger boards to charge the whole pack in parallel.

[ebastler]

Not sure what others think, but in general I don't consider a homebrew Li-ion battery pack to be a suitable beginner project. And, beginner or not, I would be wary of $1 used battery packs of unknown origin.

That battery pack will end up being used (charged) unattended. You won't have proper temperature monitoring for safety, and won't know what those batteries have already gone through before you received them. I would be very uncomfortable using this, due to concerns about fire hazards. And I certainly would not want to build one for my kid...

[Rick Law]

Not sure what others think, but in general I don't consider a homebrew Li-ion battery pack to be a suitable beginner project. And, beginner or not, I would be wary of $1 used battery packs of unknown origin.

That battery pack will end up being used (charged) unattended. You won't have proper temperature monitoring for safety, and won't know what those batteries have already gone through before you received them. I would be very uncomfortable using this, due to concerns about fire hazards. And I certainly would not want to build one for my kid...

+1!     I just put a link in my reply in another thread to this tread.

I had an "early warning".  I was playing around with ~15 years old StarTac phone battery (less than 1000mAH, if I recalled correctly).  I used it to run an LED and that was kind of fun.  It went a few cycles without problem.  One time, right after charging and I was getting ready to connect the LED back, I reached for the battery and it was way too hot to hold!

I had pliers close at hand and I used that to grab the battery and took it to the back yard.

Since then, I handle the LiIons with a lot more respect.

[nicksydney]

The battery was taken out from a Toshiba battery pack which is normally used for 10inch tablet and from the packacing it's written (C) 2011 which I assume is 6 yrs old. It is sold for $1 as the tablet itself is not sold anymore so the shop was selling it to get rid of the stock. I'm not an expert on batteries but shouldn't it be more safer to buy from a reputable brand rather than buying 18650 unknown name batteries from China from site like Aliexpress or eBay ?

Thanks

[ebastler]

The battery was taken out from a Toshiba battery pack which is normally used for 10inch tablet and from the packacing it's written (C) 2011 which I assume is 6 yrs old. It is sold for $1 as the tablet itself is not sold anymore so the shop was selling it to get rid of the stock.

From the glue residue visible on the photos, I had assumed this was a used pack, removed from some old equipment. Easy to pinch or pierce these flat batteres if you are careless during removal. I am still not sure where the glue (or adhesive tape?) would be from -- are you sure it is new?

But still, even if this were a brand new, brand-name battery: These things are not trivial to charge safely, and would later be used in an environment where you have to fully rely on their safety! I would very much encourage you to choose another starter project.

[nicksydney]

Hi,

After doing further reading on LiPo and looking more into the board I noticed the following

(1) The batteries are configured as 3S2P as I can see there are 4 leads all together connected to the board they are - positive, negative, LP2 and LP3. Looking around for BMS boards on internet the LP2 and LP3 resemble a balancer

(2) After reading on LiPo charger it make sense to get a charger + balancer for the batteries. Found the following which says a charger + balancer for 3S - https://www.aliexpress.com/item/3S-25A-lipo-lithium-Polymer-BMS-PCM-PCB-battery-protection-board-for-3-Packs-18650-Li/32767793292.html anybody has any experience with this, interested to get feedback about this ?

Thanks for the help

[Audioguru]

I found a discarded portable vacuum cleaner with a dead Ni-Cad 7.2V battery. I have some 18650 Li-Ion battery cells from my daughter's first laptop (it is about 17 years old) and two cells in series make 8.4V when fully charged and run the machine very well for a long time. I made an LM317 8.4V current limited charger for the battery.

[nicksydney]

(2) After reading on LiPo charger it make sense to get a charger + balancer for the batteries. Found the following which says a charger + balancer for 3S - https://www.aliexpress.com/item/3S-25A-lipo-lithium-Polymer-BMS-PCM-PCB-battery-protection-board-for-3-Packs-18650-Li/32767793292.html anybody has any experience with this, interested to get feedback about this ?

Perhaps someone can share their experience using similar kind of board for charging/discharging LiPo ?

[ebastler]

Perhaps someone can share their experience using similar kind of board for charging/discharging LiPo ?

Not quite sure what you are after. More likely than not, these chargers will (normally) work. But, to my earlier point, they may not implement proper safety precautions. With the potential fire hazards of LiIon batteries, I think it is important that the whole charger + battery system is designed to be single-fault tolerant. E.g. if a component on the charger fails and it suddenly starts to charge the batteries with an excessive current, there should be an independent temperature monitor that cuts off the charging if the batteries overheat.

By polling a forum, you obviously don't get a valid statistical answer on the safety of that Chinese charger. If two or three people reply "yes, this has worked just fine for me", what do you do with that information?

My advice: Buy a brand-name power bank for your son's tablet, and find a different hobby project.

[anishkgt]

(2) After reading on LiPo charger it make sense to get a charger + balancer for the batteries. Found the following which says a charger + balancer for 3S - https://www.aliexpress.com/item/3S-25A-lipo-lithium-Polymer-BMS-PCM-PCB-battery-protection-board-for-3-Packs-18650-Li/32767793292.html anybody has any experience with this, interested to get feedback about this ?

Perhaps someone can share their experience using similar kind of board for charging/discharging LiPo ?

Hey nicksydney,
I've played with Li-ion cells for a while.
Be warned that these are no thing play with and a miswiring can cause serious damage to the cell and/or to the individual using it.

Basics:
the Nominal Voltage is 3.7, meaning the voltage should not drop below that mark when a load is connected or when discharge or when stored. Li-ion cells after a full charge is 4.2v per cell so with your config you would get 8.4v and that way of wiring is called 2s3p configuration. here you would get 8.4v and 6120mAh (6.1A).

Charging:
To charge any Li-ion packs, you have to Balance charge them which helps keep all the cells balanced else one cells would be overcharged. A BMS (Battery Management System) is a crucial thing that takes care of the charging and discharging. You can get the BMS here http://www.ebay.com.au/itm/2S-8A-16A-8-4V-7-4V-Lithium-Li-ion-Battery-Cell-BMS-Protection-Board-Circuit-/201828830065?var=&hash=item2efdef8b71:m:mVfsY3QEElqBV-G2GE7fIrw. Shows how the wiring is done as well.

Second you'll need a balance wire like this http://www.ebay.com.au/itm/New-10-PCS-2S1P-Balance-Silicon-Charger-Cable-Wire-JST-XH-Connector-Adapter-Plug-/132062032892?hash=item1ebf82b3fc:g:0ZsAAOSwjDZYdxb9 which is connected to a balance port of a charger like this http://www.ebay.com.au/itm/5Amp-AC-DC-LiPo-NiCd-NiMh-Battery-Balance-Charger-for-SKYRC-iMAX-B6AC-AU-stock-/161524001980?hash=item259b94acbc:g:Ff4AAOSwj0NUkOKm works on ac 100-240VAC and a very popular model as well.

Hope this helps you.