BMS failure, troubleshooting help needed

[d3ntr0n]

Hello ES community, I've been lurking and reading for several months now so thank you for participating in these valuable and interesting forums. I have invested $2,000 in building my own E-Bike only to have the project come to a screeching halt as I tried to charge the battery for the first time. Now I am in need of some technical advice, and I wan't this to be as clear and detailed as possible so I am going to explain my build from the ground up. Skip to the question mark symbol if you don't care to read the background.

I purchased 115 Sanyo-UR18650NSX cells to build two 14s4p 52V battery packs. I tested all of the voltages on the cells to be sure they were good, and they were all reading 3.5 +/- 0.02 Volts. I used nickel strips to connect them together, which I soldered on using a high wattage iron and took painstaking care to touch the batteries for no more than 3 seconds at a time to minimize thermal damage (I didn't have a spot welder). I laser cut the end-cap for the battery so as to include main positive and negative terminal connectors as well as a mini D-sub 15 pin connector (VGA) to access the series element voltages with the BMS. The images below show one of the batteries and the aforementioned end-cap.
https://endless-sphere.com/forums/download/file.php?mode=view&id=212692
https://cdn.shopify.com/s/files/1/0...ur18650nsx_spec_sheet.pdf?2358184305725242569

I ordered a custom BMS from BesTech which is, as far as I can tell, properly sized and rated for the batteries I am using. As a note, I had planned on having one BMS and two batteries which I could swap out. This is the reason I added the mini D-sub 15 pin connection and made a custom cable to bridge the battery to the BMS. As far as I can tell this is going to work. If you are building a 52V battery pack and you like the idea of using the VGA port to run your cables through, DO NOT use a standard VGA cable. With most if not all VGA cables for PC monitors, you will cause a direct short between pins within the cable. Anyhow, the datasheet for the BMS is shown below so you can correct me if I'm wrong. At this point I should tell you I purchased a 2014 Trek Mamba, a 1500W 48V conversion kit from Hallomotor, and a Cycle Satiator charging system. Yes I am aware my battery is 52V and my kit is 48V. I've read about over-volting and wanted the ability to do so, but I mainly decided to make the 52V battery so that I could short-charge and extend the lifetime of the pack.
https://endless-sphere.com/forums/download/file.php?mode=view&id=212696

I wired the battery up very carefully, shrink wrapping every pin connection on the mini D-sub, spacing out contact points, using an organized wiring layout so as not to cross wires...the whole nine yards. I wired up the BMS exactly as shown in the attached datasheet and then I started plugging in connectors. First, I plugged the battery main negative into the BMS battery negative side. Then I connected the mini D-sub cable to the BMS, effectively wiring the BMS to the tops of every series element in the pack. However, before I could plug in the main battery pack positive cable, I smelled smoke and saw the fire coming from the BMS. I immediately unplugged it, but it is fried. Fortunately the minimum order quantity for the custom board was 2, so I have a spare. I would really appreciate any speculation as to the reason for this failure before I attempt to connect my ONLY other board. Here is a photograph of the damage. As far as I can tell, a capacitor was the link that went first, and for some reason it looks like it was the one on series element B10.
https://endless-sphere.com/forums/download/file.php?mode=view&id=212697

 

[amberwolf]

On element B10, it looks as if there is a missing transistor (this transistor is used to cause current to flow from the cell thru the large resistor (marked 101) during balancing); the pads appear to have never had anything soldered there. If that's the case, perhaps there are also other parts that were soldered incorrectly and shorted to other components? Seems unlikely, though, given the number of damaged channels.

Normally all channels are completely independent of each other, except for the series connections between each one.

It is more likely that there is either a miswire in the connector to the battery or to the BMS, so that some of the wires are out of order. That's usually what causes this kind of damage.

If so, it also usually shorts the cells out, so since your cells are all at a very low state of charge, it may have lowered teh voltage of the ones that were shorted during the incident. That may help you see which wires are wrong (assuming there is not enough damage to the wires themselves to see it, or is so much damage taht you can't tell).

You can also simply physically trace things out, or use a multimeter on continuity test, to verify that each wire goes to the correct cell group, relative to the main pack negative, in sequence.



I'd still examine the second unit to be sure it is not missing any parts from any channels, and that all channels' parts are oriented exactly the same as all others, and to the non-damaged channels on your damaged unit.