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I have a brushless DC motor I'm working with, do not have any spec. sheets for it. How can I determine if it's wired in delta or Y formation? There is nothing on the label that indicates this. Here's a picture of the label.

Motor label

TY, Fred

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    \$\begingroup\$ Can you post a pic and/or document any markings on the unit? Also, wouldn't a Y configuration require four wires while a delta only requires three? \$\endgroup\$ – Tevo D Feb 28 '12 at 18:40
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    \$\begingroup\$ @TevoD: It is not mandatory to have the neutral available with a Y conncetion, so it can still have 3 wires. \$\endgroup\$ – Count Zero Feb 28 '12 at 19:14
  • \$\begingroup\$ My motor does have only 3 wires, will try to post a pic. of the label soon. \$\endgroup\$ – fred basset Feb 28 '12 at 20:15
  • \$\begingroup\$ Thanks @CountZero. Gave me something new to research and learn. :) \$\endgroup\$ – Tevo D Feb 28 '12 at 20:39
  • \$\begingroup\$ brushless DC motors don't have to be driven like steppers, it's entirely possible to run them somewhat like synchronous three phase machines. \$\endgroup\$ – JustJeff Feb 29 '12 at 1:34
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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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  • \$\begingroup\$ Thanks for the comments Olin. Sounds like I probably have a Y configuration. What circuit are you using to control your motor by the way? Something custom designed or off the shelf? I'm still trying to get the bugs out of a custom designed board I've inherited here, got the basics working but it's blowing up driver FETs at higher currents. \$\endgroup\$ – fred basset Feb 29 '12 at 1:08
  • \$\begingroup\$ @fred: The case I mentioned was a one-off proof of concept. I used logic level FETs for the low side drivers and PNP high side drivers all manually soldered up on a ReadyBoard. Each of the 6 lines was driven seperately by a microcontroller. It is up to the firmware to never turn on the high and low side drivers of pair at the same time. \$\endgroup\$ – Olin Lathrop Feb 29 '12 at 13:05
  • \$\begingroup\$ @Olin Lathrop "I've never seen a brushless DC motor with 3 wires connected in a delta" is not proof that they don't exist. AFAIK, ALL Radio Control delta-wound BLDC motors have only THREE wires. Look at a supplier, e.g. Hobbyking, or how to DIY-wind BLDC motos e.g. southernsoaringclub.org.za or even wikipedia if you are in any doubt. \$\endgroup\$ – gbulmer Aug 2 '14 at 20:05
  • \$\begingroup\$ @Olin Lathrop "... and that makes no sense when you think about it." Why? I agree wye/star wound is 'obvious', but delta isn't too weird to imagine it would not work. A star will energise two windings (using three half-bridges, one per connection), and a delta could drive three or two windings depending on how the half-bridges are driven. \$\endgroup\$ – gbulmer Aug 2 '14 at 20:10
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Most brushless DC motors used for RC hobby use are Delta wired. Delta wiring provides a higher KV value and lower torque by a factor of 1.7 when compared to Wye connection.

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