I'm attempting to rebuild a wind generator that has a failed internal control/regulator board. Unfortunately the board components were epoxy sealed for the marine environment so not accessible or fixable.

My plan is to rectify the 3 phase output and send the unregulated DC to an external regulator circuit. I've ordered a 3-phase bridge rectifier for this and don't envisage any issues.

I'm curious about a couple of components attached to 2 of the winding leads that I haven't been able to identify and I was wondering if someone could help. The attached pictures show the rotor/stator assembly along with a magnified image of the writing on one of the components, which reads:


I'm reasonably confident that I can just connect the windings as-is (including these components) but I still would like to know what they are and what their role is.

The rotor/stator assembly

The mystery component

  • 3
    \$\begingroup\$ Most likely thermal fuses. \$\endgroup\$
    – Hearth
    Apr 14, 2023 at 0:50

2 Answers 2


They look like bimetal thermal cutoffs. They would open in case of overtemperature and close again after the temperature has dropped considerably (15 or 20°C typically). Trip point maybe 110°C. They need to be in thermal contact with whatever it is that they are protecting.

  • \$\begingroup\$ I am curious why there are two of them. The machine is 3-phase, likely Y topology (4 terminals) and since the center is used, one needs at least 3 of them to completely disconnect the generator from the downstream circuit. \$\endgroup\$
    – fraxinus
    Apr 14, 2023 at 20:57
  • \$\begingroup\$ If it's wye, the neutral may just go to ground and not ordinarily carry any current. It does appear to go to the windings. \$\endgroup\$ Apr 14, 2023 at 21:19

That was a quick turn around. Many thanks for both answers. I did a quick Google search for that component, and hey presto... I see an identical looking component from Honeywell. They would have most likely been connected to the regulator is my guess, and/or the rectifier. Either way, they are now somewhat redundant given that one of the functions (regulation) will now be outboard. I might attach one to my bridge rectifier though.

Thankyou very much for helping clarify what these components were for.

Cheers, Mike Honeywell thermostat switch

  • 1
    \$\begingroup\$ They don’t regulate anything in the conventional sense but rather act as a last line of defense against overloading the motor. \$\endgroup\$
    – winny
    Apr 14, 2023 at 9:48
  • \$\begingroup\$ These should always be included regardless of what else is connected to the machine. They're a safety device to cut off power in the event of major failures. Don't remove them. \$\endgroup\$
    – Hearth
    Apr 14, 2023 at 13:09
  • 1
    \$\begingroup\$ You should put this as a comment on the answer that actually answered your question, and then click the check-mark to the left of the answer to accept it as the solution (and give a bit of rep to the answerer) \$\endgroup\$
    – Steve
    Apr 14, 2023 at 17:55

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