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I have an Anacona Chef Range Hood. The two Halogen lights are not working. I suspect the transformer. I would like to replace it with the LED transformer. Is it possible? If possible, what type to install?

The user installation manual for the hood is here; the circuit diagram from the manual is below:

Circuit diagram of range hood

One more question, as per the diagram, the transformer has 3 wire (GYW) as output, what are these. Are they for the three setting on the push type switch (High, Low, Off), If they are, can I bypass 1 wire (Low) as most transformers come with 2 output wires. The Input is 2 wire connected to power control on/off switch is this 110/120v?

Any suggestions or answers would be highly appreciated. Thanks

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The halogen bulbs are 12 volts at 20 watts. Almost certainly the "High" setting is 12 VAC, and the "Low" setting is the same 12 VAC but through a half wave rectifier (just a diode). So, if you want to use the current switch and processor board, you'd need something that could be driven by 12VAC, both with and without a half wave rectifier.

The problem is that half-wave-rectified AC is a lot different from pure AC; it has a large DC component to it. Some LED drivers could handle it, others couldn't. I doubt you'll find a manufacturer that will sell their product as compatible with this, as it's too rare an application for them to worry about. So, you can try various products, but you may find they won't work, and you may even find that the "Low" setting damages the bulb/circuit.

An alternative would be to install your own switch, but getting it to look good would be tough.

  • Not necessarily true. I have a hood that uses 120VAC halogens, with a hi/low/off switch where low provided by a diode. I contacted a manufacturer of 120VAC LED-based bulbs with the same form factor and asked if they'd work; they refused to comment. I tried one, and it didn't blow up, but there was almost no difference between "High" and "Low". I can definitely imagine LED drivers which wouldn't take kindly to the large DC offset of half-wave-rectified power. – Daniel Griscom Jul 17 '16 at 15:16
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    With a diode blocking 1/2 the wave it would be pulsating AC and not have a DC component. This is how the early SCR light dimmers worked and could claim 50% savings. Full on only 1/2 wave was passed to the light at a maximum. When the dimmer was adjusted less of the 1/2 wave is passed depending on the pot setting the Gate voltage value. All pulsating AC not DC at all. – Ed Beal Jul 17 '16 at 16:01
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    No. SCRs are monopolar, but they're used with a bridge rectifier to provide switching on both phases, with no DC offset. Add a diode to an AC power source and you get half wave rectified AC, which has a large DC offset. – Daniel Griscom Jul 17 '16 at 17:30
  • Does half-wave AC have a DC offset? Totally depends on how you look at it. It is certainly not 'direct' in any sense of the word; it's entirely gone half the time. However it also does not reverse polarity. Of course, you can put AC and DC on the same wire; just put a transformer in series with a DC power supply. That would be rightly described as an AC voltage with a DC offset. You could describe half-wave AC as that, but only roughly. – Harper Jul 17 '16 at 22:51
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    You're up against the switching power supply of the LED. By default they are multi-voltage and sustain constant current (and this voltage) across variable voltage inputs. These naturally defeat incandescent dimmers. LEDs can be built to sense the efforts of incandescent dimmers and perform the desired dimming, but must be engineered for each dimming method. – Harper Jul 17 '16 at 23:13
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This machine has a control board full of capacitors. That is more likely to be the problem than the transformer. Either way, you're into a fairly serious repair adventure. The transformer also supplies control voltage to the board, so a transformer failure seems unlikely.

It may be possible to tap the transformer directly and use the switch to bypass the board. But now we're verging into electrical engineering.

If it's just the bulb (or if you have the machine rigged to supply 12VAC to the bulb socket), it's a matter of trying different candidate LED "bulb" products until you find one that plays nice.

Some LEDs have switching power supplies, and they will defeat the dimmer. Others (typically 12V, intended for automotive use) are simply resistor-limited, and those should work on at least one switch setting, although potentially 3dB dimmer than intended.

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Before replacing anything, be sure that the bulbs have, in fact, failed. The easiest way is probably to use a DMM to measure voltage at the bulb's contacts but reaching both socket holes at the same time may not be so easy. Competing for "easiest" is replacing one of the bulbs with a known good bulb. Or moving a suspected bad bulb to a known good socket.

I agree with @DanielGriscom: replacing halogen bulbs with LEDs which are physically and electrically compatible is very unlikely to be successful.

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