I have an AC motor with 7 different wires connecting to it, and I'd like to identify how the windings are configured. The wires are:

  • Red
  • Orange
  • Yellow
  • Blue
  • Black
  • White
  • Yellow+Green

What I've been able to gather so far is that:

  • Yellow+Green is protective earth and connected to the motor housing and nothing else
  • White is directly connected to mains neutral
  • Live mains is switched directly onto Yellow, Blue, Black, or nothing to provide 4 different speed settings
  • There's a capacitor across Red and Orange

These are the resistances I've measured between the different wires in Ohms:

Orange Yellow Blue Black White
Red 34 29 23 17.3 33.2
Orange 28.6 22.6 16.7 0.3
Yellow 6.1 12 28
Blue 6 22.1
Black 16.4

(Note that the measurements between White and the other terminals might be slightly high. They were made from the neutral pin of the AC cord of the device for convenience, whereas everything else was measured directly on the connectors on the motor.)

Given that information, how would I go about identifying the motor's configuration?


  • 1
    \$\begingroup\$ what markings are on the motor? \$\endgroup\$
    – jsotola
    Commented Jul 10, 2021 at 19:41
  • \$\begingroup\$ @jsotola There's no visible markings on the motor. I believe it to be hessaire.com/collections/mc37m-mc37v-m150-parts/products/… which says 115V / 2.4A. \$\endgroup\$ Commented Jul 10, 2021 at 20:10
  • \$\begingroup\$ Another thing I noticed about the motor is that it makes a clicking sound once per revolution when spun slowly by hand. That sound disappears as the fan gets up to higher speeds. Maybe that's some kind of starter mechanism that disengages once centrifugal forces are high enough? \$\endgroup\$ Commented Jul 10, 2021 at 20:17
  • \$\begingroup\$ Any capacitor built in or connected to it? \$\endgroup\$
    – winny
    Commented Jul 10, 2021 at 20:33
  • \$\begingroup\$ @winny There's no built-in capacitor I could identify. There's an external capacitor between Red and Orange. \$\endgroup\$ Commented Jul 10, 2021 at 20:34

1 Answer 1


Something like this:


simulate this circuit – Schematic created using CircuitLab

my reasoning was

  • the capacitor connectes to the cross-phase coil

  • ignoring the capacitor there will be no loops

  • wherever there is a lowest resistasnce those two nodes must be connected.

  • \$\begingroup\$ Which suggests the four speeds are (fastest) Black, Blue, Yellow, Off. \$\endgroup\$
    – user16324
    Commented Jul 11, 2021 at 12:10
  • \$\begingroup\$ Thank you! Would you happen to know what this configuration is called? What do you think the purpose of L6 is? I'm wondering if it's just a measurement error or the resistance of the wires leading to the motor rather than an actual coil. \$\endgroup\$ Commented Jul 11, 2021 at 15:06
  • 1
    \$\begingroup\$ if L6 is measurement error it's a systematic error. necause it's consitent across all the other measurements which show slightly higher resistance to orange than to white. it could be a sentrifugal switch but the figure seems a bit high for a switch, \$\endgroup\$ Commented Jul 11, 2021 at 20:37
  • \$\begingroup\$ Thank you. Would you happen to know how I might be able to differentiate between a systematic error and there being a low-resistance coil? I'm also curious where the centrifugal switch would fit into that schematic. Is the idea that it disconnects the capacitor once it's up to speed? What practical effect does that have? \$\endgroup\$ Commented Jul 13, 2021 at 16:32

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