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> Some ideas for a 24VAC dimmer?, Need help
Adriann
Posted: October 18, 2005 08:41 am
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All dimmer is designed to use on main power {eg 220VAC} and is imposible to control a 24VAC load. I found on net manny DC dimmers for low power but no for AC. I need a schematic for a simple 24VAC dimmer. I mention that i intend to use this for a 24VAC 48W 2Aheater element.
Please help.
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Ante
Posted: October 18, 2005 08:56 pm
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Use a PWM light or motor driver circuit, you will find many on Google. The heater element runs equally well on DC, just put a rectifier and a PWM circuit in front of it!
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Skeith
Posted: October 19, 2005 02:50 am
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Yeah Pulse width modulation (PWM) is the most effiecient way to dim lights (assuming they arent flourecent of course). Although if you dont want to use PWM you could use a mains dimmer the primary of a 24v step down transformer.


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Søren
Posted: October 19, 2005 06:57 am
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Hi,

QUOTE (Adriann)
All dimmer is designed to use on main power {eg 220VAC} and is imposible to control a 24VAC load. I found on net manny DC dimmers for low power but no for AC. I need a schematic for a simple 24VAC dimmer. I mention that i intend to use this for a 24VAC 48W 2Aheater element.
Please help.
Find a simple dimmer circuit for mains and post it here, then we can help you recalculate/rearrange the circuit for 24V.


Ante and Skeith <- Adriann asked for AC circuits, not a DC PWM control smile.gif


Regards,
Soeren


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Soeren

Whatever works... works.
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Sebi
Posted: October 19, 2005 03:28 pm
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The most simpler AC dimmer with triac and diac can't work on 24V AC, because the diac's triggerpoint above 35V. Use UJT for triggering or build it the UJT (if not available) with PNP-NPN complementary pair.
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Ante
Posted: October 19, 2005 07:41 pm
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Hi Soren,

The term dimmer might in this case be more a matter of speech than a question for a solution; a PWM circuit will get the job done unlike a “real” dimmer at this voltage and with better efficiency as well. The heater element works equally well on DC as it would on AC and with much lower emission of RFI.
The solution with a dimmer on the primary of a step-down transformer might not work either, not sure if the transformer can take the heat…… has anyone tried this? huh.gif


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Søren
Posted: October 20, 2005 10:48 am
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Hi,

QUOTE (Ante)
The term dimmer might in this case be more a matter of speech than a question for a solution;
Please reread the OP (especially the part saying "I need a schematic for a simple 24VAC dimmer.") and say that again wink.gif


QUOTE
a PWM circuit will get the job done
Then show the guy an AC PWM control, simpler than a phase angle dimmer ! devil.gif


QUOTE
unlike a “real” dimmer at this voltage and with better efficiency as well.
I realy urge you to come up with something that fits your words !


QUOTE
The heater element works equally well on DC as it would on AC
Sure, but perhaps he, for some reason, doesn't want (or cannot use) a DC dimmer.


QUOTE
and with much lower emission of RFI.
Totally BS - it will have a higher RFI, but whether this is a problem or not, none of us know, so let's give the guy what he asks for *or* ask him if he wants something else.


QUOTE
The solution with a dimmer on the primary of a step-down transformer might not work either, not sure if the transformer can take the heat……  has anyone tried this?  huh.gif
Yes, if the dimmer is of the right type, some won't, some will dim iron cores, some will dim electronic transformers (switchers) and some will dim both.

But it's not a problem dimming low voltage AC (forget about DIACs, they are dinosaurs - who needs them, we have better ways of timing wink.gif) I have made dimmers for both 12VAC and 24VAC.


Regards,
Soeren


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Soeren

Whatever works... works.
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Ante
Posted: October 20, 2005 08:25 pm
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I have read the question post, for sure! I am not familiar with AC-PWM, are you?
Why not let Adriann decide what he wants, I just gave alternatives to chose from! Nobody will benefit from you taking me apart sentence for sentence. I suggest you (instead of tying to glow me out) put your money where your mouth is and give the solution! I am sure this topic was not started for the purpose of you and me arguing about this so present the ultimate solution to Adriann.

“Yes, if the dimmer is of the right type, some won't, some will dim iron cores, some will dim electronic transformers (switchers) and some will dim both.”
Yes, but which is which…..?

“But it's not a problem dimming low voltage AC (forget about DIACs, they are dinosaurs - who needs them, we have better ways of timing ) I have made dimmers for both 12VAC and 24VAC.”

Ok show everybody the circuit then!
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Adriann
Posted: October 21, 2005 06:36 am
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Thank you guys for your answers. From youre debate I understand some important things.

1. A DC power supply is fine for this job. This is verry good because I can use my 12VAC transformer whith a voltage regulator and a NPN current booster. If i use a ajustable voltage regulator, the problem of dimming is resolved. Please corect me if I am wrong.
Question: In my knowlege, 24VDC is not equivalent whith 24VAC. What is the equivalent DC power for my iron specification.

2. This thread is a backup solution because I dont know if my project for a temperature controller will be a succes. This is my first major project.
I orderred (today or tomorrow is delivery)this iron.
http://tinypic.com/esrbc7.jpg

This tipe of iron (24VAC, 48W, 2A) is sell as a spare part for a astronomical priced soldering station and have an integrated thermocouple. I intend to make a controller whith UAA1016 and a triac for this iron and save money.
In UAA2016 datasheet is a simple circuit for this, but this circuit is designed for NTC tipe sensor.
http://www.onsemi.com/pub/Collateral/UAA2016-D.PDF

I find on net this circuits related to a homemade soldering station:

This is the tested schematic for a NTC tipe sensor:
http://tinypic.com/view/?pic=ekm6mv

And this is the adaptation for a K thermocouple tipe iron made by same person and tested whith succes by others:
http://tinypic.com/view/?pic=ekm6o4

My schematic is the combination of these
http://tinypic.com/esrbio.jpg

...but I'm not sure if everything is correct conected. If you guys wiew any errors please corect me. I repeat: this is my first major electronic project.
I dont know the wattage for resistors. This iron comes in 2 diferent models, whith 2 specification for K thermocouple (7-8 mV at soldering themperature and 20-25 mV) , so require an adaptation of opamp resistors.

So guys, if enybody is interested or want to help a novice....
I CHANGE THREAD. NEW THREAD IS THEMPERATURE CONTROLLER

This post has been edited by Adriann on October 21, 2005 06:54 am
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draget
Posted: October 21, 2005 09:21 am
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Temp control, light control, its all the same, essentially. Go DC and use PWM.
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Ante
Posted: October 24, 2005 08:09 pm
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Søren;

What with the circuit that will dim a step-down transformer without complications? unsure.gif I am really curious, it would solve an old problem I have with a wide range psu!

Ante rolleyes.gif

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Søren
Posted: October 25, 2005 06:30 pm
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Hi,

QUOTE (Ante)
What with the circuit that will dim a step-down transformer without complications?  unsure.gif  I am really curious, it would solve an old problem I have with a wide range psu!
What with it ?
Use continous drive on the gate and you can drive inductive loads (but rate the TRIAC properly for the load) smile.gif
Or go to a lamp shop and ask them about the different dimmers they have (usually they have a range for both "electronic" transformers and iron cores.



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Regards,
Soeren

Whatever works... works.
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Søren
Posted: October 25, 2005 06:38 pm
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Hi,

QUOTE (Ante)
I have read the question post, for sure! I am not familiar with AC-PWM, are you?
Exactly my point wink.gif

QUOTE
Why not let Adriann decide what he wants
Sure.

QUOTE
, I just gave alternatives to chose from! Nobody will benefit from you taking me apart sentence for sentence. I suggest you (instead of tying to glow me out) put your money where your mouth is and give the solution!
For Petes sake... Just scale down a dimmer.

QUOTE
I am sure this topic was not started for the purpose of you and me arguing about this so present the ultimate solution to Adriann.
Topics are like a box of chocolate wink.gif

QUOTE
Yes, but which is which…..?
Go talk to your nearest lamp shop.

QUOTE
Ok show everybody the circuit then!
Why, thought it was only Adriann who needed it wink.gif
If you want a circuit - make it.
I made these way back when I did CAD on my then brand new '286 in SmartPlot (or SmartSomethingElse), so I don't have anything digitized in a recognizeable format (and neither any printouts whose whereabouts I would know).
But just downscale a dimmer with constant gate drive and Bob's you uncle smile.gif


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Regards,
Soeren

Whatever works... works.
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Ante
Posted: October 26, 2005 01:53 pm
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I am sure it was “smartsomethingelse” but thanks, …. very constructive and helpful! dry.gif

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