Bafang 250W mid-drive motor rewind not going so well.(burned count: 2) - Page 1
Forum section: electronics / repair

author: Refrigerator
author_rank: Super Contributor
timestamp: August 07, 2022, 05:43:44 pm
content: When testing out my homemade BLDC driver it died and cooked my motor.Since i'm no stranger to rewinding motors i took on the task of fixing what i've done.Problem is that after rewinding the motor still doesn't work and the only conclusion that i've been able to come up with is that i rewound it wrong.The old windings had to be cut out and torn out to be able to take the stator out so i didn't really know how it was wound originally.I assumed it would be a simple A-B-C-A-B-C all the way around the stator but evidently that doesn't work.The rotor has 16 poles (N-S-N-S alternating, the usual), and the stator has 18 poles.I rewound the motor one phase at a time, winding one pole, skipping two, wind another, did this for all three phases then connected them in a Y configuration.Fortunately i can cut the windings apart and resolder them in any configuration, so rewinding is not necessary.But first i need to find out how they are supposed to be conncted, do you guys have any suggestions?

author: langwadt
author_rank: Super Contributor
timestamp: August 07, 2022, 06:36:12 pm
content: https://electronics.stackexchange.com/questions/483177/how-to-determine-brushless-dc-bldc-winding-pattern-based-on-poles-and-slots?

author: Refrigerator
author_rank: Super Contributor
timestamp: August 07, 2022, 06:42:39 pm
content: Found this cool blog, which explains in excruciating detail why i am stupid.https://things-in-motion.blogspot.com/2019/Anyways, now i know that my motor is a 18s16p, balanced BLDC motor and looks like my windings should be reconfigured to "AaA-BbB-CcC-AaA-BbB-CcC".

author: Refrigerator
author_rank: Super Contributor
timestamp: August 07, 2022, 10:09:05 pm
content: It wasn't easy and it isn't pretty but i've managed to rewire the windings and it finally works.Swapping the wires around got really confusing, because it turned into a mess of wire ends.Then the windings that were reversed had to be wired differently. I got the connections wrong at least five times.Looks like my new bldc driver doesn't like driving it at full speed, i guess it wasn't made for motors that go this fast.I should test it with another fast-running BLDC motor to make sure.Anyways, tomorrow i'll take the bike for a maiden voyage, perhaps i'll cook the motor again, who knows

author: Refrigerator
author_rank: Super Contributor
timestamp: August 08, 2022, 03:50:37 pm
content: After about 10km the motor lost power and got very stinkyI thought i could get away with low temp enamel wire but i guess i'll have to rewind it again with some better stuff.Was prety peppy while it lasted. Top speed was about 35kph.

author: Refrigerator
author_rank: Super Contributor
timestamp: August 08, 2022, 06:39:09 pm
content: Okay so after reading a few sources i can't help but want to rewind the motor again but completely differently this time.Previously i wound the wire very tightly to make sure it doesn't come off and transfers heat as well as possible.Now i want to wind the windings loosely so that i can add wedges to compress the windings very tightly against the stator.The aluminum housing of the motor comes very close to the windings so i think i might even be able to add some thermal pads to transfer the heat directly from the copper to the housing.