DCkiwi
Member
- Joined
- Sep 11, 2017
- Messages
- 183
Hello All.
I sat on this for a good week ... trying to think how to word this post, what pictures to take, and ... reflecting on whether I had just 'missed many clear warnings from fellow members' ... finally, today I did an SLS search on various search terms, EG failed BMS from china, cheap BMS, testing BMS, BMS failures, ... and some more. pretty much nothing came up.
So it is with a heavy heart that I deliver this post to you all. Not so much that I got 'ripped off' a few measly $$, but more that I had no idea that tech had gotten this trashy ... hadn't been WARNING other members ... but also ... that no-one here had warned me ... about these cheap BMS's. So here goes ... *deep breath*
Background: recently I have decided to get a whole heap of cells into production. So I ordered a variety of the 'standard' cheap BMS's we have all seen ... before assuming that my $$/precious batteries would be safe, I thought it prudent to test them ... so I built a jig, and here's what happened:
sorry for bad images, new camera is literally on its way to me now ...
so the setup (above) is pretty basic. the two purple cells wired in 2s go through a linear regulator (LM317 based) to simulate the first cell in a 6s string. that way I can dial up/down the 'cell' voltage, and see what happens to the output of the tested BMS.
as you can see, cell #1 is well under 2.8V and the output is still ... Vbatt (!!).
my testing has revealed that it makes no difference to vast majority of BMS's even if the balance lead/harness is completely disconnected (!!!) which to me would seem to be the worst type of battery failure, as then there is just no info to 'MS' the 'B'.
I did pause and think before posting this. it did strike me as unlikely, but this is not a dream ... it's true!
NB votes CAN BE CHANGED, so put your current situation now, and if your situation changes, then you can come back and update your vote. the poll result can be useful for us all, please participate! cheers all well, I goofed, evidently not all polls can have votes changed. perhaps its cause its a public poll, or no end date ... dont know ... my bad.
I sat on this for a good week ... trying to think how to word this post, what pictures to take, and ... reflecting on whether I had just 'missed many clear warnings from fellow members' ... finally, today I did an SLS search on various search terms, EG failed BMS from china, cheap BMS, testing BMS, BMS failures, ... and some more. pretty much nothing came up.
So it is with a heavy heart that I deliver this post to you all. Not so much that I got 'ripped off' a few measly $$, but more that I had no idea that tech had gotten this trashy ... hadn't been WARNING other members ... but also ... that no-one here had warned me ... about these cheap BMS's. So here goes ... *deep breath*
Background: recently I have decided to get a whole heap of cells into production. So I ordered a variety of the 'standard' cheap BMS's we have all seen ... before assuming that my $$/precious batteries would be safe, I thought it prudent to test them ... so I built a jig, and here's what happened:
sorry for bad images, new camera is literally on its way to me now ...
so the setup (above) is pretty basic. the two purple cells wired in 2s go through a linear regulator (LM317 based) to simulate the first cell in a 6s string. that way I can dial up/down the 'cell' voltage, and see what happens to the output of the tested BMS.
as you can see, cell #1 is well under 2.8V and the output is still ... Vbatt (!!).
my testing has revealed that it makes no difference to vast majority of BMS's even if the balance lead/harness is completely disconnected (!!!) which to me would seem to be the worst type of battery failure, as then there is just no info to 'MS' the 'B'.
I did pause and think before posting this. it did strike me as unlikely, but this is not a dream ... it's true!