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can I use a rectifier as a dimmer for halogen light bulbs? Answered

I am wiring a custom exhaust hood, and am wondering if I could use a IN5402 rectifier diode rated at 3 amps, 200 PIV connected in series with a 1.9 amp halogen light load, running at 120 Volts AC in order to dim the lights in the hood at about half bright? Wondering specifically if I will run into any problems with the longevity of the "dimmer", or the life of the bulbs? Also wondering if any one might know how I could make a very simple circuit that could slow a fan down to about half speed. I am using single pole double throw bat handle switches to make a high and low setting. High will just go straight through, and low will go through the dimmer or speed reducing module.

Thanks rik

4 Replies

lemonie (author)2012-04-05

A single diode will half-wave the supply to ~50% current.


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mpilchfamily (author)2012-04-05

Check out the instructables on the right hand side here. The Variable AC Power Supply with a twist would be just what you need. All it consists of is a wall outlet and a dimmer. The dimmer will be able to control the light without any problems. It will also work well with a fan.

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Jack A Lopez (author)2012-04-04

This sounds good in theory, so I think the next thing to try is actually wiring it up to see how it looks, because the flicker might be noticeable... or it might not.  That's why I suggest trying it.

The PIV is a little bit close to the peak reverse voltage of the mains supply.  I mean if it were truly 120 Vrms, the the peaks would be at plus or minus square root of two times that, or 1.4142*120 = 169.71 V.

You know, I think they make triac type dimmers
 that can handle that amount of current, and there is even a knob you can turn to set the amount of dim-ness.

Something like one of those little dimmer switches might work on the fan too. 

Actually that Wiki page titled "Dimmer", linked above,  had lots of ideas, zany stuff too, like rheostats made out of salt water. 

I'm not sure about using the diode-in-series trick with a fan motor, because that trick gives a non-zero DC component, and something about feeding DC to a inductive load makes me uneasy.  But my intuition has been wrong before, and it might be something fun to try, just to see what happens.

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frollard (author)Jack A Lopez2012-04-04

+1 for each.

It's simply easier/cheaper when considering the fire hazard to go with a commercial dimmer.

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