Thread Rating:
  • 0 Vote(s) - 0 Average
  • 1
  • 2
  • 3
  • 4
  • 5
Motorola Phone Battery BMS Terminals
#1

Hi all,

I have been fortunate to score a whole heap of Motorola phone Batteries, all in VGC. I am trying to figure out a way to use them and I was hoping someone might know how the BMS functions on this battery. At the top of the batteries there are two pins which have around 7.5 volts in all of them. On the back are four terminals none of which show any voltage. I found a dud one with zero voltage and broke it down and it was very difficult to get the 18500 cells and split them apart. I damaged one cell almost immediately. I was wondering why I cant leave them intact and solder a BMS to the four terminals making use of a very sturdy housing and wiring ready to go. At 7.4 volts I am assuming it is a 2S battery and so even if I parrallel them all I will still have a series problem that is unmanaged, unless I can figure a way to use those four terminals. Of interest the older batteries have three terminals on the back and they show the voltages of both the cells in series.


Attached Files Thumbnail(s)
           
Reply
#2
Usually, not always, phone batteries don't have a bms that can be interfaced with. It might have a small bms internally, though (would measure about 6mm x 20mm or so) and would only be rudimentary type of bms, namely over/under discharge protection.
Normally 1 pin is Pos, 1 is Neg, 1 is Temp. I don't recall what the 4th pin would be used for, unless it's for the main bms (in the phone) to actually see the different voltages of the cells.

Can you provide a picture with what voltage and resistance readings you get probing the various pins?
Proceed with caution. Knowledge is Power! Literally! Cool 
Knowledge is Power; Absolute Knowledge is Absolutely Shocking!
Certified 18650 Cell Reclamation Technician

Please come join in general chit-chat and randomness at Discord Chat (channels: general, 3d-printing, linux&coding, 18650, humor, ...)
(this chat is not directly affiliated with SecondLifeStorage; VALID email req'd)
Reply
#3
All four pins show no voltage but have continuity and a resistance between 3 of them. The two outer terminals have the higher resistance. I have seen one of
the batteries marked positive and negative on the outer two terminals. Do you think I would be safe using these batteries without a BMS if I limited the maximum voltage and charged slowly? I want to use them in a very consistent discharge charge regime for optimum cycle life






Reply
#4
Ahhh, bigger bms than I thought.

Ok, from what I can gather here, the acros would be:

BP = Battery Pos
BG2 = Battery Gnd
CP = Charger Pos
CG = Charger Gnd

BG2 and CG are possibly connected together on the pcb. The CP will only come live when voltage is applied externally to that port and wakes the bms up for charging.

And that pack looks to be a 3s1p pack, not 2s. And they are rated for about 700mAh from what I found. Now, I suppose it's possible they are connected in parallel, but you said you got 7.2V, which kinda throws off. Is there a cell under the pcb? I can't tell in the image. If so, then maybe it's a 2s2p configuration.
Proceed with caution. Knowledge is Power! Literally! Cool 
Knowledge is Power; Absolute Knowledge is Absolutely Shocking!
Certified 18650 Cell Reclamation Technician

Please come join in general chit-chat and randomness at Discord Chat (channels: general, 3d-printing, linux&coding, 18650, humor, ...)
(this chat is not directly affiliated with SecondLifeStorage; VALID email req'd)
Reply
#5
there are four cells in total I have seen voltages from 7.5-8.0 across all the batteries I have pretty sure its 2s2p. I figure there is no voltage as a safety feature on the exposed back of the battery. On one pack it had positive and negative marked on the outer two terminals so I just have to figure out what the inner two terminals are. If I can charge each pack individually then connect all of them in series I may be able to build a usefull battery.

Whoops clarification the battery pack pictured only has three terminals on the back of the battery sorry my mistake.
Reply
#6
Might be why there are 4 pins. The phone might have a resistor that causes a certain resistance between 2 of the pins, and that turns the bms on. Some power tool battery packs are like that.

Have you done a search of the bms numbers that's silkscreened on the pcb? I can see DIACEL & AP202, but that's only partially the numbers as there's a grey goober still on the pcb Tongue
Proceed with caution. Knowledge is Power! Literally! Cool 
Knowledge is Power; Absolute Knowledge is Absolutely Shocking!
Certified 18650 Cell Reclamation Technician

Please come join in general chit-chat and randomness at Discord Chat (channels: general, 3d-printing, linux&coding, 18650, humor, ...)
(this chat is not directly affiliated with SecondLifeStorage; VALID email req'd)
Reply
#7
i doubt those bms boards were designed for series use.
parallel you could get away with.
when 1 pack hits lvd the others get hit with more load and they disconnect in a domino effect.
in series the unit that disconnects first has the full string voltage across its bms.
it will likely get damaged.
Reply
#8
Thanks for the input on paralled vs series kc8adu I was considering running them in parallel and just taping all the cases together, maybe 10 at a time and then into a bus bar. 7.4 nominal is a hard voltage to find an application for but I was thinking of putting it through a voltage stepper and into a grid tie inverter. If I charged the battery from the two discharge terminals at the top of the battery and limited the voltage to say 8.1 volts and no lower than 7 to 7.1 and did the duty cycle slowly over 24 hours could I get away with bypassing the BMS ?
Reply
#9
I don't see why putting them in series would cause a problem. If 1 turns off, voltage stops. No cells within the string would see full voltage. After all, a battery cell doesn't see high voltage if another is disconnected.

However, you could take 3 units and connect them in series and put a load on the whole string and monitor each pack voltage and temperatures.

In another since, you could always just completely disconnect the bms all together. But that would require opening up each pack to remove the bms board.

Trying to charge by bypassing the bms, with it still connected, could be very difficult, depending on how the bms is designed. It might be designed that if it senses power flowing backwards, it shuts down to protect the cells. Can you take one of the boards out so we can see what the other side looks like?
Proceed with caution. Knowledge is Power! Literally! Cool 
Knowledge is Power; Absolute Knowledge is Absolutely Shocking!
Certified 18650 Cell Reclamation Technician

Please come join in general chit-chat and randomness at Discord Chat (channels: general, 3d-printing, linux&coding, 18650, humor, ...)
(this chat is not directly affiliated with SecondLifeStorage; VALID email req'd)
Reply
#10
I will do a full autopsy in the morning (midnite here) of a pack with four terminals on the battery. I will get the curcuit board out completely and work out a wiring diagram. I really want to make this work and save these cells as a stack of them are brand new still in the factory box, and I can get more.
Korishan likes this post
Reply


Who read this thread?
19 User(s) read this thread:
Sean (08-10-2019, 06:45 AM), 3xtr3m3 (08-10-2019, 05:27 PM), kc8adu (07-24-2019, 05:14 PM), BitcoinBandit (07-29-2019, 03:09 AM), juanjo57 (08-10-2019, 09:21 AM), RikH (07-30-2019, 10:32 PM), ajw22 (07-24-2019, 02:41 PM), Wolf (07-25-2019, 12:25 PM), chuckp (07-25-2019, 10:57 AM), Bubba (07-26-2019, 12:25 AM), gpn (08-11-2019, 02:59 AM), HughF (08-01-2019, 09:06 AM), Oz18650 (08-10-2019, 04:19 AM), Geek (08-12-2019, 01:10 AM), Chiptosser (07-26-2019, 01:23 AM), Stefaan De Ridder (Yesterday, 12:29 PM), PAF (07-24-2019, 02:10 PM), Korishan (08-10-2019, 11:19 AM), jiggyjonboat (08-06-2019, 01:54 AM)

Forum Jump:


Users browsing this thread: 1 Guest(s)