How to tell if brushless DC motor is wired delta or Y?
I've never seen a brushless DC motor with 3 wires connected in a delta, and that makes no sense when you think about it.  I would assume 3 wires means Y configuration with the center not available, but of course the datasheet is the right place to get this information from.

With a 3-wire Y configuration, you can go thru 12 steps per phase.  Each wire can be forced low, forced high, or left open.  Walk thru the sequence and you will see there are 12 steps as the field rotates thru one phase.  This scheme wouldn't work with a delta configuration because you wouldn't be able to achieve some of the combinations of full, partial, and no current thru each of the windings in the desired directions.  A nice side effect of this configuration and using 12 drive steps is that a wire is never switched directly between active high and active low.  In other words, proper drive automatically includes dead time between the low and high side drivers being on.

I recently did a project with a 3 wire brushless DC motor with the coils connected in a delta.  I measured the center point for each of the 12 drive steps, and they were quite evenly spaced.  This was a VCR tapehead motor being repurposed as a proof of concept test by the customer.

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