Bafang 750w mid motor power issue

liftman666

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I have an electric trike that I built with a Bafang 48V 750W BBS02B BBS02 Mid Drive Motor powered by a 48volt 20ah battery pack with a 48V 30A BMS protection board.

The trike is an EZ TRIKE and I have been operating this E trike for over a year and then one day it just stops my screen on my DC18 goes blank. I checked the voltage being supplied to the system and I was only reading 3.1 volts.

I opened up the battery pack and took a voltage reading from positive to negative on the battery pack and was getting 53.1 volts. The voltage coming out of the BMS was only 3.176 volts. When I connected the charger to the battery pack, the BMS started to put out 53.3 volts. So, I put the battery pack back on the trike and went for a ride lo and behold after .2 miles my DC18 goes blank. So again, when I checked out the battery pack, I got the same results as before with 53.1 volts on the battery but only 3.178 volts on the BMS output.


The supplier of the battery pack sends me a new BMS even though the battery pack was out of the one-year warranty. So, I installed the new BMS on the battery pack and then I plug the charger in to bring it up to full charge. I installed the battery pack onto the trike and took it for a ride. At .6 miles the same thing happened again DC18 goes blank. Again, I open the battery pack and get the same readings as before with the old BMS.


My question is does anyone out there have any idea why my 750-Watt mid drive motor keeps damaging the BMS in my battery pack?
 
I think you are going at this from the wrong end, your motor isn't the problem. Your battery is the culprit. Most likely you have a bad cell. An 18650 cell would have a charge of 3.7 volts. Your 48v battery says it has 52 volts. A 48v system should charge to 54.6 volts. I think you've got one cell clocking in at 1.1 volt. According to Google this can throw off your whole bms. Since you are already in there, you can test each cell and see if this is the case. Let us know what you find. I am posting the Google response here:
Screenshot_20241125-185128_Chrome.jpg
 
I think you are going at this from the wrong end, your motor isn't the problem. Your battery is the culprit. Most likely you have a bad cell. An 18650 cell would have a charge of 3.7 volts. Your 48v battery says it has 52 volts. A 48v system should charge to 54.6 volts. I think you've got one cell clocking in at 1.1 volt. According to Google this can throw off your whole bms. Since you are already in there, you can test each cell and see if this is the case. Let us know what you find. I am posting the Google response here:View attachment 17275Ii did not say that it was fully charged at 52v. the BMS started to put out voltage at 52v, and that was just a number that popped into my head. when I do charge it fully, I do get the 54.6 volts. I just ran a test on the battery pack and it was showing 52.2 when it cut out. then it would show 3.7 volts coming out of the BMS and the battery from positive to negative reads 53.1v.
 
Youtube has a video by Luna Cycle, "Testing Bad BMS" and also VRMinde has a video, "Dead BMS, how to test it". I don't know your battery set up, but they show you how to carefully test the white connector pins which go to each cell. You can also test the groups that are in parallel to see if their group voltage is correct. I'm not an expert at this, but it seems to me, this would be the next logical step.
 
I think you are going at this from the wrong end, your motor isn't the problem. Your battery is the culprit. Most likely you have a bad cell. An 18650 cell would have a charge of 3.7 volts. Your 48v battery says it has 52 volts. A 48v system should charge to 54.6 volts. I think you've got one cell clocking in at 1.1 volt. According to Google this can throw off your whole bms. Since you are already in there, you can test each cell and see if this is the case. Let us know what you find. I am posting the Google response here:View attachment 17275
I agree. Problem is, you can laboriously find the offending cell, but if your pack is old, you'll probably lose another one soon. And cells that charge up don't always have any real storage capacity left. I recycled my 6 year old, 52 volt porta pack that serve me on 3 bikes. I found 2 bad cells, replaced them, lost another one a month later. If you want to play musical cells, mo' power to ya. No sarc, my hat's off.
 
I agree. Problem is, you can laboriously find the offending cell, but if your pack is old, you'll probably lose another one soon. And cells that charge up don't always have any real storage capacity left. I recycled my 6 year old, 52 volt porta pack that serve me on 3 bikes. I found 2 bad cells, replaced them, lost another one a month later. If you want to play musical cells, mo' power to ya. No sarc, my hat's off.
The battery pack was only 15 months old with only 10 cycles and mileage less than 100 miles. I ordered a new battery from someone else and they claim their battery is good for 15,000 cycles.
 
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ugh. You are buying bottom-of-the-line batteries. That second one is branded "Nojoke" (i.e. No Joke. So the seller has a sense of humor).

You should expect problems on bottom-of-the-line batteries I'm afraid. Sellers prey on the uneducated buyer and unfortunately not everyone knows this stuff in detail, so a lot of people get taken.

Both your 'before' and 'after' batteries have 30a BMS limits (although neither of them say whether this is peak amps or continuous, which is a big deal to know), so they are both equal. On paper at least. You should ignore the claims of 100-1000w capacity, and 0-1400 watts as they are completely meaningless.

Your BBS02 demands a max of 25a, so if your battery is rated for 30a 'continuous' current, you should be fine on that score. But if that battery manufacturer is using a 'peak' value (and maybe thats why they are mum on which) then you almost certainly have an underpowered BMS. Maybe its only good for 20a (I just made that up... its always a lesser number). If so, it would manifest itself as the BMS 'pops' as soon as the current demand exceeds the few seconds allowed under the peak load... and it shuts down. The only way to switch the battery back on again is to hook the battery up to a charger, which will reset it. Then you can go ride again, but as soon as the amp draw hits that peak value for a hair too long the BMS will pop again and you are back to repeating the process.

Testing a battery's output after the BMS pops would yield a really low output number like you are seeing, while the cells themselves test out to be fully charged.

I think there is a very good chance your 25a-continuous-output motor is exceeding a BMS continuous limit that may be right at or just below your battery BMS' continuous output limit, but the peak limit is 30a so you get some performance out of it for a short time until you ask too much of it and poof.

Try setting your BBS02's current limit to 10a and see if that makes the problem go away. Your motor output will be hobbled but the test will be valid.
 
uh oh... I looked down to the bottom of the Amazon listings you mention and sure enough, your first battery says its BMS is 30a 'maximum' so thats the peak value. Very likely what I described above is what your problem is on your original battery.

The second battery makes no such disclosures, but I think for a battery priced at about 1/3 what a pack that size should cost, we can expect they cut the same corner.

Batteries like this give acceptable output for light to medium duty hub motors, but not for a mid drive. Especially a Bafang BBSxx where those motors can peg the meter at their peak output numbers and stay there for as long as you put the hammer down.
 
ugh. You are buying bottom-of-the-line batteries. That second one is branded "Nojoke" (i.e. No Joke. So the seller has a sense of humor).

You should expect problems on bottom-of-the-line batteries I'm afraid. Sellers prey on the uneducated buyer and unfortunately not everyone knows this stuff in detail, so a lot of people get taken.

Both your 'before' and 'after' batteries have 30a BMS limits (although neither of them say whether this is peak amps or continuous, which is a big deal to know), so they are both equal. On paper at least. You should ignore the claims of 100-1000w capacity, and 0-1400 watts as they are completely meaningless.

Your BBS02 demands a max of 25a, so if your battery is rated for 30a 'continuous' current, you should be fine on that score. But if that battery manufacturer is using a 'peak' value (and maybe thats why they are mum on which) then you almost certainly have an underpowered BMS. Maybe its only good for 20a (I just made that up... its always a lesser number). If so, it would manifest itself as the BMS 'pops' as soon as the current demand exceeds the few seconds allowed under the peak load... and it shuts down. The only way to switch the battery back on again is to hook the battery up to a charger, which will reset it. Then you can go ride again, but as soon as the amp draw hits that peak value for a hair too long the BMS will pop again and you are back to repeating the process.

Testing a battery's output after the BMS pops would yield a really low output number like you are seeing, while the cells themselves test out to be fully charged.

I think there is a very good chance your 25a-continuous-output motor is exceeding a BMS continuous limit that may be right at or just below your battery BMS' continuous output limit, but the peak limit is 30a so you get some performance out of it for a short time until you ask too much of it and poof.

Try setting your BBS02's current limit to 10a and see if that makes the problem go away. Your motor output will be hobbled but the test will be valid.
How do I set the BBSO2's current limit to 10a?
 
I'm guessing you're on a budget. I think to keep you and the bike alive you will have to pay a little bit more. I ran a search on Aliexpress listing samsung, LG or Sanyo cells and this is what came up in a soft pack. The branded cells are much safer and more stable. Maybe M@ can tell us how this one looks.
Screenshot_20241204-134713_Chrome.jpg
Screenshot_20241204-135106_Chrome.jpg
 
I'm guessing you're on a budget. I think to keep you and the bike alive you will have to pay a little bit more. I ran a search on Aliexpress listing samsung, LG or Sanyo cells and this is what came up in a soft pack. The branded cells are much safer and more stable. Maybe M@ can tell us how this one looks.

Yes, I am on a budget. I am retired disabled with a fixed income. But I will keep these in mind if and when I need another battery.
 
How do I set the BBSO2's current limit to 10a?
I did a full how-to here. The article includes links to the tools that let you get into the rich settings interface that is available for BBSxx motors.


This is actually an update to an article I first wrote in 2021. As such I let all the descriptions of what every setting is reside in the original article. So while the article I am linking shows very refined, kinder/gentler settings, and those are the ones I would use as examples of what to do, the full explainer is the original article.

And while I point to the BBSHD in the title, the 'HD is the same as the '02 insofar as these settings are concerned. So these settings and methods apply to you just as they do for a BBSHD.

To answer your specific question, you want to go to the Basic Screen and set the Current Limit down from its default (which is probably 25a) to 10a. I say 10a because that is a number so low it is likely to be underneath your battery BMS' Continuous current limit. Probably well underneath it. If your battery has a 30a peak, I would expect the continuous limit is 15a, or if you are lucky its 20. I would try 10 and if the bike is reliable, go to 11, then 12 and so on until the problem reoccurs and you know where the upper limit is.

Unfortunately, reducing the current limit reduces the usefulness of the motor. The amps translate to torque on the drivetrain. The more amps, the more oomph you have accelerating from a stop. Take that away and the motor is gutless. But what we're trying to do here is just figure out the problem. I think long term if you want proper performance you will need a proper battery with a 30a continuous current limit (you don't want to match at 25 because there can still be some overlap that pops the bms if you don't allow for a little fudge in your bms' rating).
 
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