BMS voltages on C- & P-

18650

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Jun 19, 2019
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I installed a 36v BMS, all seemed fine, when I tested the voltage I noticed

B- Battery is at 36.6v
P- Load is at 18v (approx)
C- Charger is at 18v (approx)

The device drawing the load would not work at 18v

Has anyone come across this ?
 
18650 said:
I installed a 36v BMS, all seemed fine, when I tested the voltage I noticed

B- Battery is at 36.6v
P- Load is at 18v (approx)
C- Charger is at 18v (approx)

The device drawing the load would not work at 18v

Has anyone come across this ?
Maybe the individual cell (voltage) balance leads were not hooked up properly - interesting that you only have 1/2 of 36v.
 
OffGridInTheCity said:
Maybe the individual cell (voltage) balance leads were not hooked up properly - interesting that you only have 1/2 of 36v.

I was extremely careful to check all the balance leads. The battery was recycled so it has solder in place for all the balance leads.

I was really hoping for a response from someone who has a battery BMS and can measure it or who has actual relevant experience of the issue I have raised.
 
Are you sure the Positive connection is common terminal? Which bms are you using? pictures of the unit wired up would be helpful
 
If this is the Bluetooth boards, make sure it is switch on in software...

This is why I made something like this to test these boards. If you send me a photo ill see if I have the same and will try and test it or see if I can replicate it with mine.

 
Korishan said:
Are you sure the Positive connection is common terminal? Which bms are you using? pictures of the unit wired up would be helpful

Sorry for delay in reply, I must have missed the email notification


image_sjbftu.jpg


I have since found that this BMS unit was 16amp, I originally planned a single 10s setup but ended up witing two together, which are 20A, so I have now ordered a 35v
 
18650 said:
This is new one I bought


image_lduack.jpg
It looks like the illustration shows where you could connect. But not all at once.
The pictures below illustrate the 2 ways to connect a typical BMS
image_smtptz.jpg


The BMS most likely has 2 sets of Mosfets. You can control the charge and load separately.
 
Your balance leads in the photo are not plugged in... were they connected when you took your measurement?

Make sure its connected correctly with all cells in balance otherwise the board may have went into protection mode.
 
CrimpDaddy said:
Your balance leads in the photo are not plugged in... were they connected when you took your measurement?

Make sure its connected correctly with all cells in balance otherwise the board may have went into protection mode.

Yes all wires go to right cells

I unplugged it as I am replacing it.


Bubba said:
It looks like the illustration shows where you could connect. But not all at once.
The pictures below illustrate the 2 ways to connect a typical BMS
image_smtptz.jpg


The BMS most likely has 2 sets of Mosfets. You can control the charge and load separately.

It is the type with different port.
 
So I got the new 35A BMS, I plugged in the balancing cables, I have not soldered the thicker negative cables yet but I thought I would check the voltages to see if they resolve the problems above.

So I put one probe on the Battery Main Postive terminal, I then tried each of the Negative solder points on the new BMS,

All three show the full load of the battery of 37v

So my conclusion is that the old one was either faulty or could not cope with the 4 extra amps
 
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