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First pack build - BMS issue
#1
Hi everyone,

I'm making my first attempt at building a pack:

High quality, but used Samsung LI-iON 18650's arrange as 4s

Input from a AC powered Supply set to 16.8VDC and 1.0A max

The Cells all tested good on an Obus charger and have similar mAHr results
Cells currently holding about 3.8V each.

BMS:   cf-4s30a-a      


I have it wired up as per the wiring diagram and everything is good until I insert the last cell.


When un-powered, the first 3 cells total about 11.8V.
     When the last cell in inserted, the TOTAL pack voltage falls to about 11.2V

The cells are all correctly orientated.

When measured individually, the cells are all good, and Total around 15V, so I believe the problem is in the BMS.



Any suggestions woulld be appreciated, Thanks!
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#2
Wink 
It is hardly possible to make any analysis statement without picture, circuit, voltages, currents, and so on.

What i can say is either the BMS is bad or you have wrong connections. But, the hardly does any help.

Big Grin
1 kWp in Test
4 kWh battery target - plus Mobile Home battery
Ultra low cost
Electronics ? No clue. Am machinery engineer.
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#3
Finally able to get some pictures ...


Cells:    Samsung   ICR18650-26J     

BMS:     CF-40S30A-A   



Wiring arrangement:

This is to test out the BMS, so I rigged up a system that uses a 4x cell holder, while still allowing the balance leads to connect to each cell...


Power is applied through a barrel connector to the P+ & P- solder pads.   (Problem occurs before applying power)


Balance lead B- and Pack negative connected to the B- Pad.
Pack Positive connected to the B+ Pad.


Balance leads are soldered on to nickel strips and firmly held in contact by cell holder springs.

All connections read good on a continuity checker.  Voltages on the Balance Cable are the same as when reading on the individual solder pads on the PCB.


What's Happening:

When inserting the cells the Balance leads show appropriate voltages for B1-B3.

The Total Voltage at B3 is 11.8V (All Cells are around 3.8V)

If I measure at B+ (Pack +), without the 4th cell inserted, I read 11.2V.

If I insert the 4th Cell, the B+ voltage remains the same. (11.2V), when it should be reading approx. 15.6V

The Cells are all good, and I have tried multiple cells with the same results.



Any suggestions, other than 'get a new BMS'??    Smile
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#4
How is the cell holder wired from cell to cell? Picture of that wiring could help as well.

But, just based off the above, it would seem to me that you have cell 3 and cell 4 wired in parallel instead of series. That'd be the only explanation I can see, other than your bms is busted.
Proceed with caution. Knowledge is Power! Literally! Cool 
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#5
The holder does a back and forth arrangement:



(The negative of each cell goes to the spring)
DCkiwi likes this post
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#6
did you connect B- to the B1- cell, I can't see on the photo

and also B+ to B4+ ?

the balance wires and the extra wire need to go to the pack

best regards

Stefaan


Attached Files Thumbnail(s)
   
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#7
Yes,

B- is connected to the Negative lead of the pack.

B+ is connected to the Positive lead.

B4 Balance lead is also connected to B+ on the PCB.

If I insert B4 in the holder so only the negative side is touching, I get the expected 15V (or so).


The weird 11.2V on B+ is present with only the first 3 cells installed and doesn't change when the 4th cell is fully inserted.

I'm thinking there is probably a short somewhere on the board, but I can't see it visually and I don't have a schematic.
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#8
removed. Nonsense from me.
1 kWp in Test
4 kWh battery target - plus Mobile Home battery
Ultra low cost
Electronics ? No clue. Am machinery engineer.
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#9
(04-29-2019, 02:20 PM)sunkmail Wrote: Yes,

B- is connected to the Negative lead of the pack.

B+ is connected to the Positive lead.

B4 Balance lead is also connected to B+ on the PCB.

If I insert B4 in the holder so only the negative side is touching, I get the expected 15V (or so).


The weird 11.2V on B+ is present with only the first 3 cells installed and doesn't change when the 4th cell is fully inserted.

I'm thinking there is probably a short somewhere on the board, but I can't see it visually and I don't have a schematic.

why did you make that connection?
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#10
(04-29-2019, 02:38 PM)Stefaan De Ridder Wrote:
(04-29-2019, 02:20 PM)sunkmail Wrote: Yes,

B- is connected to the Negative lead of the pack.

B+ is connected to the Positive lead.

B4 Balance lead is also connected to B+ on the PCB.

If I insert B4 in the holder so only the negative side is touching, I get the expected 15V (or so).


The weird 11.2V on B+ is present with only the first 3 cells installed and doesn't change when the 4th cell is fully inserted.

I'm thinking there is probably a short somewhere on the board, but I can't see it visually and I don't have a schematic.

why did you make that connection?
Because it is correct.
1 kWp in Test
4 kWh battery target - plus Mobile Home battery
Ultra low cost
Electronics ? No clue. Am machinery engineer.
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