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I have a KitchenAid 48-inch range hood liner for custom range hoods. Overall, it's a decent appliance, and I like it. It's advertised (on the linked page and others) as coming with "Four LED Lights with Night Light Setting." Interestingly, the user manual refers to swapping out the "halogen" lamps, so I think this model used to ship with halogen bulbs and now ships with LED bulbs. But, apparently, that's the only thing they changed. You may see where this is going...

One thing we noticed after install as that the lighting is perfect at full brightness but visibly flickers in the low setting ("night light setting" as described). It's extremely unpleasant, so we just haven't been using the low setting. But today my curiosity got the better of me, so I pulled up the wiring diagram (page 17). And then I quickly saw the problem.

The appliance "dims" the bulbs by inserting a simple diode in series upstream from the bulbs. This results in skipping every half wave of the 120V/60Hz source. I think this is called a 1/2-wave bridge dimming circuit (I could be wrong)? In theory, it cuts 50% of the power, thus dimming the bulb by 50%. I'm sure this worked fine with halogen bulbs, but LED bulbs (or, at least, these LED bulbs) do not like that.

The bulbs it shipped with are (4) MaxLite 6.5MRGD930FL/JA8/G2 LED bulbs (that is the exact manufacturer and model bulb). I know I could simply solve this problem by replacing the bulbs with halogen bulbs, but (A) I prefer sticking with LED bulbs, (B) for very technical reasons that I won't detail (having to do with a current-sensing make-up air system), I cannot replace these bulbs with halogen bulbs, and finally (C) minor nit, KitchenAid would probably find a way to argue that increasing the bulb wattage voids the warranty, even though the wires are clearly of sufficient gauge.

So, if I want to be able to use the "night light setting," I will need one of two things. Either:

  1. Preferably, a replacement MR16 GU10 500-lumen 3000K 120VAC enclosed-fixture-rated damp-location-rated LED lamp that supports this type of dimming (I saw a couple suggestions that bulbs containing full-wave bridge rectifiers should work, but I don't know how to find that information, or if that's even correct); or,
  2. The simplest possible electronic component that I can drop in-place of the in-series diode to achieve the 50% dimming without the flickering (I know—this, too, would probably void the warranty ... I might be okay with that).

Anyone have any suggestions on how I can make this appliance lighting work correctly?

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  • If you're worried about voiding the warranty, it's still under warranty. Contact KitchenAid and complain to them that it's not functioning properly because the bulbs flicker when dimmed. Let them deal with fixing it. It might be that they simply shipped a faulty unit.
    – FreeMan
    Commented Feb 6 at 17:46
  • If only it were that simple. I might still try that again and hope I get a better support person, but trying to explain this problem to a customer support person is like trying to explain nuclear fission to a kindergartener. The lights are technically bright on the high setting and dim on the low setting, so the support person doesn't think there's a problem. Commented Feb 6 at 18:05
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    Oh, and, also, because this is a hood liner meant for installing in a custom hood, if they decide the whole unit needs to be removed, then the entire hood has to be deconstructed (which is not something I will let them do). It would ... just be easier if I could fix this myself. Commented Feb 6 at 18:07

1 Answer 1

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The answer to 2 is a capacitor. It would have to be AC rated, to at least your supply voltage.

My rough calculations for the capacitance would be: If P = V²/R, then R = V²/P, so the effective impedance of a lamp is about 120²/6.5 = 2200 Ω. Four in parallel is then about 550 Ω.

To halve the current, we want to double the impedance. The impedance of a capacitor is X = 1/2πfC. So C = 1/2πfX. f is 60 Hz. So C = 5 μF, or something near that (possibly 4.7 μF) - it's not critical.

So a 5μF AC rated capacitor. For safety, add a high resistor in parallel to it (say 330 kΩ to 1 MΩ), so you don't get a nasty zap of the capacitor when servicing the thing.

Adjust the capacitor higher (brighter) or lower (dimmer) as desired.

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  • Sounds brilliant. And, to be clear, you're saying "remove the diode, replace it with the capacitor+resistor," correct? Commented Feb 6 at 21:22
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    @NickWilliams yes. The capacitor replaces the diode.
    – Simon B
    Commented Feb 6 at 22:20
  • And one more question: Since the resistor is merely in place to dissipate residual energy in the capacitor when the power is turned off, it shouldn't need to be a high-wattage capacitor, should it? 1W should be plenty? I'm looking at getting DigiKey part numbers 330KWTR-ND and 565-4663-ND, which I think should work. Commented Feb 6 at 23:38
  • (Scratch 565-4663-ND ... still looking for the right capacitor.) Commented Feb 6 at 23:54
  • Capacitor-wise, the best thing I can find that meets the criteria of 4.5-to-5 µF rated at 120VAC or higher is something like DigiKey part number 2368-CFC-4.75-ND. My only concern is that these say they're "expressly designed for ceiling fans," but as long as the characteristics are right (capacitance), I don't see why it wouldn't work. Commented Feb 7 at 0:07

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