Help wanted to identify part of e-bike BMS - Page 1
Forum section: electronics / repair

author: spa2036
author_rank: Newbie
timestamp: August 23, 2025, 10:49:22 am
content: I have an e-bike battery pack that does not take a charge. The batteries in the pack are OK and so is the charger. So far I identified a diode that blocks in both directions so I assume this part is broken. I have tried to search the internet with the inscription on the part but sofar no luck.The markings are DK ( zener?) followed on next line with 1 I GB9 or so in SMB size format.This battery pack has model no: EBG360-140P3S14. I have tried to contact the manufacturer Phylion Battery Co Ltd in China, but they do not respond, neighter did Batavus ( bike brand).How can I proceed in repairing this BMS/controller? Please find attached a photo of D49 which is the defective diode.Thanks in advance

author: gamalot
author_rank: Super Contributor
timestamp: August 23, 2025, 11:05:03 am
content: THe one with marking CV is SMF4L45CA, and the one with DK is SMF4L60CA:https://www.littelfuse.com/assetdocs/tvs-diodes-smf4l-datasheet?assetguid=d2ba8fab-1de3-4176-8530-f36ecb0b8799They have a very high breakdown voltage (55V and 66.7V) so it's normal that you measure bidirectional blocking.

author: Psi
author_rank: Super Contributor
timestamp: August 23, 2025, 11:16:31 am
content: Odd silkscreen marking for a non-polarized component.

author: gamalot
author_rank: Super Contributor
timestamp: August 23, 2025, 11:24:56 am
content: Quote from: Psi on August 23, 2025, 11:16:31 amThere is nothing wrong with the silk screen of the device in the picture.The silk screen with polarity mark is like this:

author: mikerj
author_rank: Super Contributor
timestamp: August 23, 2025, 11:30:09 am
content: Quote from: gamalot on August 23, 2025, 11:24:56 amThe silk screen suggests a polarised component, but the part is not polarised. Your picture shows a component, not the silk screen for it.

author: spa2036
author_rank: Newbie
timestamp: August 23, 2025, 11:57:21 am
content: It is possible to test the SMF4L45CA ( D29) with my DMM and a simple component tester from FNIRSI that indicates it is a zener diode with Vf = 0.5V. While testing D49, SMF4L60CA I have no readings either direction. My component tester tells me "Broken or dammaged component". Does that means that maybe D29 is suspicious of being broken because of getting a reading?The two Mosfets on the back of the pcb mounted to the heatsink were easy to identify, NCE80H12, but the two next to the diodes I have a hard time identifying them.

author: spa2036
author_rank: Newbie
timestamp: August 23, 2025, 12:00:57 pm
content: I am not trying to modify the battery pack I woud like the pack to accept a charge. When connected to the charger it tries to charge at 42V and one second later the charger stops charging.

author: gamalot
author_rank: Super Contributor
timestamp: August 23, 2025, 12:02:33 pm
content: Quote from: mikerj on August 23, 2025, 11:30:09 amOh, I see. I used to call the markings on components silkscreen. My mistake!

author: gamalot
author_rank: Super Contributor
timestamp: August 23, 2025, 12:07:22 pm
content: Remove D29 from PCB. If you can still measure a voltage drop of about 0.5V in any direction, then it is definitely damaged.

author: spa2036
author_rank: Newbie
timestamp: August 23, 2025, 12:28:26 pm
content: Finally identified the two other two mosfet's as F540NS.

author: spa2036
author_rank: Newbie
timestamp: August 23, 2025, 08:32:03 pm
content: Replaced D49 and the battery is taking a charge.Thank you all for helping me out!