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A windmill produces AC voltage, with increasing voltage as the turbine spins faster. If you know the max safe RPM, you could find the associated max safe voltage (V_safe). Additionally, when the leads of a turbine are shorted with each other, it induces a braking effect.

If you place a Zener diode with a V_safe breakdown voltage (maybe slightly lower for a safety margin), wouldn’t the AC voltage above V_safe go towards braking the turbine? I’m interested because of two reasons:

  1. Preventing the turbine from spinning itself apart.
  2. The V_safe I’m interested in would actually be the max value of a switch mode buck converter.

Really badly drawn turbine with two leads and two zener diodes

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    \$\begingroup\$ Zener diodes are not meant to dissipate the power associated with the application you are describing. \$\endgroup\$
    – vir
    Commented Dec 29, 2023 at 3:10
  • \$\begingroup\$ What generator power level are you considering here? How does that compare with the largest Zener diode you've seen? \$\endgroup\$
    – Transistor
    Commented Dec 29, 2023 at 3:10
  • \$\begingroup\$ @vir, I just assumed the power would be dissipated as heat or the magnetic braking in the copper coils of the generator in the braking process. \$\endgroup\$
    – kevinbuiied
    Commented Dec 29, 2023 at 3:12
  • \$\begingroup\$ @Transistor, this is all very hypothetical. But if I were to build anything like this, it'd be for a small wind turbine, maybe 100 watts. \$\endgroup\$
    – kevinbuiied
    Commented Dec 29, 2023 at 3:13
  • \$\begingroup\$ 100 W might be achievable. I can find 50 W versions in stud-mount. I'm not sure that it's the right solution though. \$\endgroup\$
    – Transistor
    Commented Dec 29, 2023 at 3:19

1 Answer 1

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You can place a zener+bjt clamp after rectifier so clamp is on DC side, otherwise (clamp on AC side) you would need to double it for both polarities.

enter image description here

Of course, the bjt has to be mounted on big heatsink. You can put a power resistor between Vcc and collector to split overall losses (like half on R and half on bjt).

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  • \$\begingroup\$ The capacitor is probably unnecessary. \$\endgroup\$
    – MOSFET
    Commented Mar 1 at 4:59

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