Car alternator conversion Back-emf

stepus

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Sep 3, 2019
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Hi, i had converted two alternators, first the old one is 90A bosch, and there i have original rotor but i did it turned on latche to smaller diameter and glued neodym magnets from burned R/C motor - rotor have original iron teeths but with magnets.

second is 120A alternator, i made my own rotor, from aluminium on CNC mill.
I have a question about Back-EMF from these "motors" - see picture.
What causes this distortion ? I thing I have a small gap between stator and rotor ?
Because if i connect motor in delta and turns it by hand, i feel its hard to turn, if i unconnect two phases, so they are no longer joined into a "circle" i can turn shaft easily. First motor iam running on delta - draws a lots of current about 20amp/6s lipo at no load at max RPM, but it have serious torque, it pulls me on second gear to wheelie on my ebike.. and power is about 2,5kW.
https://www.youtube.com/watch?v=ZZY_ar65OoA&t=1s

second motor draws much more current so i cant run it in delta - but i want it. Now i run it in WYE and powers my tricycle - but i want more power wich offers delta connection.

So what causing inducting current in coils that trying to stop motor ?
Sorry for my english, iam a czech.
Thanks for advise.
 

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