Hi group! My current sailboat repower project will be off the shelf components with reduction gear, but I have been pondering going direct drive with a slow speed homebrew BLDC motor at some point in the future. I am thinking large diameter with at least 8 maybe more poles, phases Y-connected. Radial flux so warping of the rotor plate from heat and torque won't be as likely to scrape the magnets on the coils, and so I won't have to be so concerned with small amounts of axial play. Water cooled so a slow turning fan won't allow overheating. Yes I know this will be an expensive project and I will end up rewinding the stator multiple times but it is mostly about pushing the envelop and seeing if it can be done practically, using an off the shelf controller like the 300a 48v Kelly unit. One question is whether I will get power loss from induced current in the cooling lines if I use copper or stainless tubing. I figure on running the coolant in and back out of each individual coil core. Will induced currents simply cancel each other out? Also it seems that with lots of coils I could tailor the impedance a bit by wiring each phase in series, parallel, or series/parallel. Does this sound right? The larger diameter (maybe 22" or so) should give me lots of low speed torque, correct? And more poles reduce cogging? Going way out in left field how about say 30 poles, 90 coils? Could go series, or 15 parallel pairs in series, or 10 series of 3 coils, or 5 of 6, etc. With heavy gage connecting wire to reduce losses, might this work, so that the same basic motor could be tailored for different operational needs by rewiring? Another reason for lots of poles is so I could use cheap off the shelf magnets and not have to use custom mags. Really just pondering at this stage. I hope anybody with a background in 3 phase motors will chip in with their thoughts. The idea has sort of nested in my brain and it won't go away no matter how many beers I drink.
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