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pot dimmer vs triac&diac dimmer

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vidi

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So I'm talking to my friend about dimming a 120V, 500W light. One version of the circuit is to use a triac and a diac and a controller.
**broken link removed**
Another thing I was thinking about was to throw a 1MΩ potentiometer into the mix and dial down the voltage on the light.
So I guess the question is, what would be the disadvantage be, if any, to just using the pot to control the amplitude of the voltage to the light as opposed to using the triac to control the pulse duration?
 
Kinda hard to judge, since your linked image says:

This Article & Circuit is Copy from www.free-circuit.com Without permission. You can read the original at www.free-circuit.com.

(Obviously not native English speakers ...)

Try some other way of posting the image.
 
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wow, thats odd, I just copied the image URL. It's definite if you've been to the site that they are indeed not English vocabularists :)

Here, check this site, you'll get the idea.

**broken link removed**
 
So I guess the question is, what would be the disadvantage be, if any, to just using the pot to control the amplitude of the voltage to the light as opposed to using the triac to control the pulse duration?

Think about the power involved. That is a 500 watt dimmer. You want a resistor capable of dissipating about 500 watts or so. Depending on ohmic value that is around a $175 to $200 USD potentiometer not to mention the heat that would pour off it or how inefficient it would be. I can buy a $9.95 dimmer at the hardware store that will use a triac and handle 600 watts.

On another unrelated note, the forums like it better when you upload images rather than link to them. When an image is removed from a URL it leaves a blank with a dreaded little red x so people searching a subject a year from now can't follow a thread.

Ron
 
On another unrelated note, the forums like it better when you upload images rather than link to them. When an image is removed from a URL it leaves a blank with a dreaded little red x so people searching a subject a year from now can't follow a thread.

What he said.

To make it easy, here's what you can do:
Create an "album" (click on "My Account" up there and select "My Albums"). Click the link to upload images, then either copy the image first to your computer, or just point to the URL of the image. The image will then be in your album. Select that image, then click on the image link that is given below and copy it. Paste this into a message and Bingo! the image will appear. As Ron pointed out, this prevents the problem of the URL of the image changing, or the image being removed from the website, or the website going belly-up.
 
I'll be sure to post screen captures of any schematic I'm interested in for the future. Sorry bout that.

So. What I'm hearing is that the main disadvantage is lack of efficiency? The other, only slightly less worrisome one being the heat throw. I guess I could get down with that as a reasonable argument against just throwing a pot on there.

Thanks.
 
Using a rheostat (which is what you'd be using, not a potentiometer; in any case, a variable resistor) is the brute-force way to do it. It simply throws away a part of the energy that would otherwise go to the light bulb as heat. Very wasteful.

The "electronic" solution, such as the circuit you're asking about, is a lot smarter about using energy. That's why we have triac-based light dimmers instead of giant wirewound resistors dimming our lights nowadays.

There are tons of dimming circuits out there in web-land. Some of them might even work ...
 
lol! for sure, I've seen a bunch of them at this point. I think the main problem is that no one ever explains them in project format, like use this kind of a connector for the thyristor and all that, and don't forget to add a heat sync to the backing plate, and so forth. It's a wild world of do it yourself. It can be really daunting to do simple things sometimes.
 
lol! for sure, I've seen a bunch of them at this point. I think the main problem is that no one ever explains them in project format, like use this kind of a connector for the thyristor and all that, and don't forget to add a heat sync to the backing plate, and so forth. It's a wild world of do it yourself. It can be really daunting to do simple things sometimes.

You go ahead and add a heat sync. Personally I will add a heat sink to my components. Now if you will excuse me I need to sync my Blackberry smart phone to my laptop computer and have a beer while I wait. :)

Couldn't help it...........

Ron
 
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