3s or 2s packs, voltage at battery terminals much higher than at dc in/out terminals of PCB board, solutions pls

Thread Starter

ju1234

Joined Sep 15, 2018
7
I have made more than one power packs using used 18650 batteries. I have tried it with several different sets of batteries and 3 different PCB boards.

I have a 3 different 2S board, and 1 3S board. I have used them with several different batteries. All batteries were originally charged in the PC and then removed from the PC battery or they were individually chrged in a single battery charger. All batteries when tested individually or in series. were good showing more than 4.3V. I thought the maximum they are charged to are 4.3 or so. Some of them read 5.3 (taken from the same PC battery), may be you can explain that too.

Ok. I connected them to the PCB boards. Measured at PCB output: Only one pack shows correct 8.7V (2S). All others I tried are drastically low. A 3S shows only 7.8V, 2 of 3S packs show only 6.7 - 5.8V. I have checked all the connections over and over. I have changed the way they are connected, temporary allegator connections and soldered connections. They all show the same problem

Can you please explain why? and what is the solution? Thank you very much.
 

KeithWalker

Joined Jul 10, 2017
1,224
What are the PCBs that you are connecting the batteries to and how are the batteries wired together (i.e. single, several in series or in series/parallel) ? Without that information, we can not even try to answer your question.

Lithium Ion batteries are usually charged up to a maximum of 4.2 volts. Anything higher than that seriously depletes the life of the battery.
 
Last edited:

Audioguru again

Joined Oct 21, 2019
1,931
I agree and so does www.batteryuniversity.com that an older Lithium Cobalt battery has a maximum charged voltage of 4.20V.
Modern Lithium-ferrous-something battery cells are charged at about 3.2V or 3.5V.
There are some very new Lithium Graphene cells that are charged to 4.35V.
A Lithium Cobalt cell is ruined if it has been discharged below about 3V. Most products detect 3.2V then disconnect the load.
 

Thread Starter

ju1234

Joined Sep 15, 2018
7
I have used a 3S 20A balanced board purchased on Ebay. I have connected it according to the diagram the seller had on their site. The board has connections marked 0V, 4.2V, 8.4V and 12.6V and the + and -. I have connected three 18650 cells in series, say cells 1 , 2, 3. The positive end of 1 is connected to 12.6V, the negative of 3 to 0V. The bridge between 1-2 to 8.4V on the board and 2-3 to 4.2V (I have tried reversing the position of these two as well, with same result). The + and - terminals are the input (charge) output terminals. I have used the these terminals to charge the pack and it appears to charge fine.

With the multimeter, I measured voltage at various points. The voltage measured at the battery terminals is 12.6V. The 0V, 4.2V, 8.4V and 12.6V points on the board measure corresponding voltage. However the voltage at input/output terminals is never more than 8.4V. I have checked the integrity of all the connections. Today, just to be sure, I took all the soldered connections off and re-did all of them. I even used different set of cells. Same results.

Similar story with a 2S board as well. That one puts out only 5.3V-6.2V when It should be close to 8.4.

I do have one 2S board which is functioning correctly.

Thank you.
 

TeeKay6

Joined Apr 20, 2019
572
I have used a 3S 20A balanced board purchased on Ebay. I have connected it according to the diagram the seller had on their site. The board has connections marked 0V, 4.2V, 8.4V and 12.6V and the + and -. I have connected three 18650 cells in series, say cells 1 , 2, 3. The positive end of 1 is connected to 12.6V, the negative of 3 to 0V. The bridge between 1-2 to 8.4V on the board and 2-3 to 4.2V (I have tried reversing the position of these two as well, with same result). The + and - terminals are the input (charge) output terminals. I have used the these terminals to charge the pack and it appears to charge fine.

With the multimeter, I measured voltage at various points. The voltage measured at the battery terminals is 12.6V. The 0V, 4.2V, 8.4V and 12.6V points on the board measure corresponding voltage. However the voltage at input/output terminals is never more than 8.4V. I have checked the integrity of all the connections. Today, just to be sure, I took all the soldered connections off and re-did all of them. I even used different set of cells. Same results.

Similar story with a 2S board as well. That one puts out only 5.3V-6.2V when It should be close to 8.4.

I do have one 2S board which is functioning correctly.

Thank you.
Unless there is only one version of balance board sold worldwide, I think we need more info. Board mfr? model? photos or links to photos of boards (showing both sides of board and any markings)? photos of your setup including the board and any wires, batteries, etc so that we can verify correct hook-up, etc.

Other posters have already noted that it is important to charge a battery according to its "chemistry". Every type of battery has different charging rules; as noted, check www.BatteryUniversity.com for more specific info. Any battery that has a 1cell voltage of 5.3V has already been overcharged and very likely damaged.
 

KeithWalker

Joined Jul 10, 2017
1,224
With the multimeter, I measured voltage at various points. The voltage measured at the battery terminals is 12.6V. The 0V, 4.2V, 8.4V and 12.6V points on the board measure corresponding voltage. However the voltage at input/output terminals is never more than 8.4V. I have checked the integrity of all the connections. Today, just to be sure, I took all the soldered connections off and re-did all of them. I even used different set of cells. Same results.
You have not given us any information about what your circuit boards are except that they are for charging batteries with up to 3 cells. Are the PCBs just battery charging circuits or do they include a supply to drive external circuits? I don't understand what the input/output terminals are for. What is the supply for the charger and what is the output supposed to be if it has a built in supply.
KW
 
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