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I have a range/stove hood with a really strong and loud blower motor.

It's so strong that when we moved into our small house, the inspector made me disable the highest 3 speeds/CFM fan levels (600CFM) - which I did by cutting the wire marked "strong" (there's also a "medium" and "weak" - all run from the control panel to the fan motor.)

The "medium" uses 2.9A, the "weak" uses 2.6A, and I think the "strong" (which I cut) used around ~3.2A.

Can I put a resistor onto the "strong" wire at my cut, and reduce it from probably its original ~3.3A to ~2A in order to create a slower/quieter option on my currently useless setting?

Ohm's law seems to tell me to use a 60ohm resistor - (120V/2A) = "X" resistor ohms.

I have extensive experience with 12V systems and solar, and much residential AC electrical, but I have never added a resistor or tried something like this.

The model is the "Ancona Inserta".

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    \$\begingroup\$ The power the resistor will have to dissipate is (60 Ohm)*(2A)^2 = 240W. That would be a little heater. \$\endgroup\$
    – Eugene Sh.
    Nov 11 at 20:11
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    \$\begingroup\$ The calculation you have should be rearranged to show the power dissipated in the resistor, i.e. the power that is not going to the fan. You'd still be in the area of 120W for power dissipated which is hefty. Maybe a triac motor controller at a fixed setting? \$\endgroup\$
    – vir
    Nov 11 at 20:17
  • \$\begingroup\$ Not a good idea. \$\endgroup\$ Nov 11 at 20:23
  • \$\begingroup\$ Eugene - you are off by a factor of 2, but maybe the underlying point still stands. \$\endgroup\$
    – Steverino
    Nov 11 at 20:38
  • \$\begingroup\$ @vir - Thanks for the clarification. Any details on a Triac motor? \$\endgroup\$
    – Steverino
    Nov 11 at 20:39
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Limiting the current with a series resistor might work, but as above it comes with its own set of problems. But the real issue is that multi-speed AC fans often use a capacitor or multiple/tapped windings to achieve different speeds. If that is the case, a simple series resistor will not do what you want.

Contact the manufacturer to see if a smaller motor is available. My hood came with 400 W and 600 W options for the motor.

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  • \$\begingroup\$ This: >>>> But the real issue is that multi-speed AC fans often use a capacitor or multiple/tapped windings to achieve different speeds. $$$$ You need a motor controller probably that can 'trick' the motor into thinking it's seeing something other than 60Hz. Try a ceiling fan controller... Just might work (and not violate code!) i.e. homedepot.com/p/… $$$$ Simple to try and cheap enough if it doesn't work, you're not out big $$$ \$\endgroup\$
    – Kyle B
    Nov 11 at 21:20
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This is a poor idea for two reasons:

  1. It's probably against your building/electrical code to make modifications to a fixture in your kitchen that aren't approved by the manufacturer (this is definitely a fixture, not portable electronics).

  2. Adding a resistor would decrease the current by turning a significant amount of electrical power into heat. This is wasteful, there are practical difficulties with getting rid of that heat, and you don't want your kitchen to be on fire.

Potentially, with a good enough look at the internals of the range hood, someone could come up with a way to wire in a lower power option that wouldn't involve a resistor, which would address issue #2, but not #1, unless you got that information as a recommendation from the manufacturer.

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  • \$\begingroup\$ It's clearly not uniformly against local codes to modify the fan, since I was instructed to cut/disable the high setting to be code compliant. \$\endgroup\$
    – Steverino
    Nov 11 at 20:49
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Anyhow, if you want to go ahead with a resistor, better try connecting in series with the lower speed winding. Forget the high speed motor wire, and use high switch output for medium motor winding, medium switch output to low motor winding, and low switch output to the resistor series with low motor winding. This way the current reduction is less and also power losses. Resistor calculation is not easy, because motor is not a simple resistor. You have to reduce from low speed 2.6 A to about 2 A. That is 23% lower, so you can try with (120/2.6)= 46 ohm *23% --> 11 ohm . Use an ajustable winded resistor, rated power > 50 W.

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  • \$\begingroup\$ I wired a simple light switch dimmer into what had been the "high" speed wire for the motor. It works perfectly at lower speeds now. \$\endgroup\$
    – Steverino
    Nov 13 at 19:09

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