BMS problem

Baptiste

10 mW
Joined
Dec 9, 2017
Messages
27
Hello
I am not able to run my bms. I did the wiring correclty and when I try to charge the batteries (p+p-) nothing is changing after hours.
When the bms is connected to nothing there is a tension of 14v on p+p- (cells have a nominal charge of 3.6) but when I connect bms to an amplifier it goes down 2.5v and it is quite annoying in need a minimum of 5v to run my amplifier.
I am completely lost. :/
 
can you post a picture of your bms or the part description? all of them are wired differently but to me it sounds like something isn't wired correctly.
 
The bms is this one : 4S 30A 14.8V Li-ion Lithium 18650 Battery BMS Packs PCB Protection Board Balance.
So i ve got one red wire between each group of two cells ( 4 times 2*3.6V in series). A red wire and the B+ wire are connected to one extremety of the series of batteris (the positive one) and A black wire and the B- wire are connected to the other extremety ( the negative one).
And then the p+ and p- are connected to the charger or the amplifier
 
I have a similar bms, heres a picture of what mine looks like when I had all the wires solder onto it. Is that similar how you got you wires hooked up?


a 4s bms.jpg
 
No i didn t used B1,2,3 pins. I thought i could either use those or the big wire with four small ones. With what should I connect B1,2,3?
 
b1 goes between battery 1+ and 2-, b2 goes between battery 2+ and 3-, and b3 goes between battery 3+ and 4-, below is a picture that shows how it would go if connected directly on battery.

a 4s bms battery connection.jpg
 
Here are the photos
 

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maby the bms is more like 4s 12.8V lifepo bms? discharge the 4 cells down to 3.3V and connect the bms....discharge-charge okey and charge stops @3.6V singel cell-14.4Volt total pack this bms wil be for lifepo.I have wrong bms here from the same company:eek:rder 3s li-ion/lipo bms and they send 4s lifepo bms :mrgreen:
 
no first check the bms wurks on lower voltages to be sure the board is not for 4s lfp.

The cells you use are Li-ion 3.6-3.7V talking about the bms now.
 
it looks like you got it connected right, because you can connect them through the 4s connector or solder through the actual circuit board.
But I think joachim is right, the batteries you are using are li-ion which require 4.2 volts to fully charge, and the board is made for lifepo4 which are fully charged at 3.65 volts. The part number on your board is the same as on my board and mine is designed for lifepo4 and works excellent with those batteries.
It will never fully charge li-ion batteries.

This is what you got
b 4s bms 1.jpg
b 4s bms 2.jpg
 
All right thank you so much :) .
I unfortunately still have got a problem: when I connect the bms to something that needs a source of energy( in my a case; an amplifier), the tension delivered (which was 14v before I made the connection) goes down to 2.5V. This seems very strange. Have you got an answer to this problem?
 
This might be because I have unpruposely shortcut the p+ and p- but I don t know if the problem was already there before the shortcut.
 
If the BMS 'sees' any cell going below the cutoff point, it will disconnect the load. Measure each cell voltage at the BMS connector and make sure they are all within the healthy range. Try measuring them with the load connected also. Even if it was a LiFePO4 BMS, it should allow discharge with 3.6v cells.
 
Yes my cells are respectively at 3.58, 3.48, 3.47, 3.45V. I can understand that the bms will not charge the cells any futher because one is already almost too high (3.58v) but why does the bms prevent the cells from discharging when I try to supply my amplifier. Why does the tension goes from 14v to 2.5v? Should I connect the amplifier on the B+ an B- instead of p+ and p- ?
 
Baptiste said:
Should I connect the amplifier on the B+ an B- instead of p+ and p- ?

You could try that just to make sure the cells are good. It should work but won't give you protection. You could also charge that way but would need to babysit the cell voltages to make sure none go over 4.2v.
 
Ok thank you. :D
But you really don t have any explanation to the fact that the tension goes down while using the batteries?
 
Hook the volt meter to the lowest of the cells, and watch it's voltage when you connect hte load to the BMS.

I'd guess that on connection, the capacitance in the load (amplifier) is drawing so much current that the voltage of the cell(s) drops below the BMS's cutoff point,

-or-

the BMS has a current limit, causing it to shutdown due to too high an inrush current from the amplifier.
 
Baptiste said:
Ok thank you. :D
But you really don t have any explanation to the fact that the tension goes down while using the batteries?

It seems the BMS is tripping for one reason or another. That's what causes it to cut the output. With no load, it will show full pack voltage but this is going through a resistor on the BMS.

Either a cell is going too low (and this can be for a millisecond), or the current is going too high (again, this happens very fast) or your BMS is just bad.

If you bypass the BMS by going to the B+ and B- terminals and the cell voltages look OK with the load running, then I would assume the BMS is bad.
 
All right thank you for this piece of advice but could you be more specific when you re saying a cell is going too low/ the current is going too high?
 
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