Daly BMS lov-voltage cuttoff not working

I have a 8s 4p lifepo4 battery pack with a daly bms (this is the closest one I could fine but mine doesn't have a separate charging port: https://www.amazon.com/DALY-LiFePo4...fix=daly+bms+8s+24v,aps,409&sr=8-2-spons&th=1) One day I found out that the low voltage cutoff doesn't work! I'm not sure how low the voltage could go but my eclectic scooter would come to a craw and I didn't want to push it. I took apart my battery and checked the balance leads and everything seems to be fine. The BMS still puts out power. I'm not sure if the balance charging and overcharge protection is working. Is there an easy way to test it? Or should I just get another bms? If everything else works fine on the bms and just not the LVC then I would still be fine with that and I'll just be more careful.

(Btw I built the battery myself but I think I did a pretty good job. Its not the first one I made)

If anyone has any ideas I would really appreciate it!

I think more information is needed to give you a proper answer.

Have you wired/built your system to by-pass the BMS when discharging?

If not the above, then I would try the following:

Measure each individual cell voltage, measure total string voltage, measure current on each balancer lead, measure total string charging current and see if anything is off.


Good luck!


Edit:

I found this:

fechter said:

Once the BMS trips for whatever reason, most of them are looking for the discharge port voltage to come back up to near pack voltage to reset. If the load (controller) is disconnected or turned off, a resistor in the BMS is supposed to bring the output voltage back up to where it can reset. This is a safety feature to prevent the BMS from turning on against a shorted load. The problem is some controllers take a little current even when they are turned off, just enough to prevent resetting. Even if the controller is disconnected, I've seen some that just can't get the output high enough to reset (bad design or construction).

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In this thread: https://endless-sphere.com/forums/viewtopic.php?f=14&t=110087 - There might be some useful information about Daly BMS's for you there.

First step would still be to determan what voltage you are at.
The bms is not supposed to trip if things work as they should, the controller should turn down the power and eventually stop before that happens.

Sajeel said:

fechter said:

Once the BMS trips for whatever reason, most of them are looking for the discharge port voltage to come back up to near pack voltage to reset. If the load (controller) is disconnected or turned off, a resistor in the BMS is supposed to bring the output voltage back up to where it can reset. This is a safety feature to prevent the BMS from turning on against a shorted load. The problem is some controllers take a little current even when they are turned off, just enough to prevent resetting. Even if the controller is disconnected, I've seen some that just can't get the output high enough to reset (bad design or construction).

Click to expand...

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I believe this is what happened to me, I had to remove my battery and charge it directly. After that it worked fine but with no LVC. It was around 23 volts when this happened but I was able to charge it to 28 volts. I would think that this would have fully reset the LVC, but maybe not?

j bjork said:

First step would still be to determan what voltage you are at.
The bms is not supposed to trip if things work as they should, the controller should turn down the power and eventually stop before that happens.

Click to expand...

If you mean that my speed controller should cutoff the battery before the voltage does too low, it wont. Its a razor e300 and the controller is very simple, I'm sure at a really low voltage (maybe less than 20) it will shut off but by then my battery would have been long dead.

I have not wired it to bypass the bms when discharging and until now the LVC worked normal.
My scooter is running normal right now, but with not LVC.

Measure each individual cell voltage, measure total string voltage, measure current on each balancer lead, measure total string charging current and see if anything is off.

Click to expand...

If I do this I'm not sure what would be normal, I'm still somewhat new to battery systems and bms. Do you know of a video showing how to do this? I also don't have a multimeter with one of those loops to measure current (I forget the name). But are those things accurate enough for the small balancing current?

Also in case I didn't make it clear my BMS is putting out normal voltage through the p- wire.

methods said:

Failure Mode
Output mosfets shorted like diode

Indicator of Failure Mode
Does not stop for LVC (tho it tries)
Runs VERY HOT, far hotter than normal
If powered down you can actually measure this diode pass-thru from Blue to Black

I.E.
With a NEW unit in GOOD order you get OL (Open Circuit) between the Battery and Pack lines. Once in Failure Mode you get a Diode reading, anode pointing away, so basically... allowing any ground to return while dumping 500mV. This (at 30A) puts 15W of heat on the tiny device...

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This is from https://endless-sphere.com/forums/viewtopic.php?f=14&t=110087 (thanks for showing me that)
Ive tested resistance between the p- and b- lines and its open when the balance leads are unplugged and no voltage is comming thru the battery. Does this mean the mosfets are fine? Im not sure how I would measures diode pass-thru (still somewhat new to this)

Is it open in both directions from P- to B- *and* from B- to P-?

If yours has no separate charge port, then your P-/C- are the same wire connection pad on the BMS, right? (may not even be a marking for C-) This is what goes out to the controller and charger (and B- is where the most negative cell's negative end connects).

So the FETs for each of those are installed on the board "back to back" in series, such that if you measure across them from P- to B-, one direction (red on P- black on B-) you may measure a connection, but the other way (red on B- black on P-), you may measure open circuit, because a failed discharge FET will let current pass, and the still working but turned off charge fet would block current from getting into the pack (from P- to B-) but wouldn't be able to block it from flowing out of the pack (from B- to P-) becuase the charge FET is a diode in that direction even if it's off.

If the FETs are all working you'll read open in both directions when they're disabled.

If any of the FETs are failed shorted, you'll read a low resistance or a diode in that direction even when they're disabled.

Note that under some conditions a multimeter on Ohms will not detect this failure, but it should do so in Diode mode (looks like --|>|-- on the control).

Certain meters may not read it even under taht condition because of the way they work, but if you measure from the center of the FETs where they all connect (usually at the tabs) to B- and then the same to P-, you can read the individual sides of the charge/discharge switches even with those meters.

Use Diode Test feature on DMM with balance taps removed (BMS off).

Good = OL both directions
Bad = diode voltage in either direction

What's happening is that one mosfet array is short circuited allowing you to measure the body diode of the other mosfet array.

Resistance measurement is not what you want for this.



-methods

Final Conclusion from my Failure Analysis

[youtube]b3lKlv81oQ4[/youtube]

-methods

Not a big daly fan I see. I read an open circuit using both resistance and diode modes. What else might be the problem?

I'm a business client of daly, i can ask them about this, we had one BMS where the LVC did not work, so far. What can i ask them specifically. PM me. There a lots of fakes out there as well, defect being rebranded and sold on aliexpress. Please also send me the url where you bought it and maby can verify if its real.

The Battery Doctor said:

I'm a business client of daly, i can ask them about this, we had one BMS where the LVC did not work, so far. What can i ask them specifically. PM me. There a lots of fakes out there as well, defect being rebranded and sold on aliexpress. Please also send me the url where you bought it and maby can verify if its real.

Click to expand...

The non working cut voltage is TRUE at those BMS's! the EV company I work had to replace that brand bms at one battery(one customer battery w/ daly bms, but we have many those bms at stock..I need to test those to put out results!), I was doin 15A rate discharge in a 67V battery and it went to 15V, glad I pushed stop button at machine! battery was very hot after discharge!(under 50V is the high cells IR (internal resistance) graph zone, producing much more heat! NON safe zone!) It was a 20Ah 67V 16S battery, machine dischargin @ 15A rate (electric scooter average @ +40km/h flat)

Maybe Daly need to recall some series of those bms's... similar to onewheel company case, +100k possible recall. and to equilibrium this the FloatWheel poped out! at lest it wont stop suddenly working throwing person out of tha board..! that VESC controller is some of the recent best invents for all kind of EV's plus opensource. Thanks for developers work!