Author Topic: Problem with DIY dimmer  (Read 8001 times)

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Offline panossTopic starter

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Problem with DIY dimmer
« on: August 19, 2018, 07:06:17 am »
I have built the dimmer shown in the attached file.
(the parts are the ones shown in the drawing)

It works fine with incandescent bulb and works fine with a Tecsol soldering iron I had.
(here let me note that I want it for this job, to regulate the temperature of the soldering iron)

I burned the Tecsol and I got a ZD-70D Double Power Tweezers 20Watt / 130Watt ...
Well, with this soldering iron the dimmer does not work !!!
Its temperature is constantly at the maximum no matter the position of the potentiometer !!


Why is this happening?


I tried again with the incadescent lamp and then with a motor: the dimmer with these works fine!
Only with this particular soldering iron I get this strange bahavior!

 

Offline james_s

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Re: Problem with DIY dimmer
« Reply #1 on: August 19, 2018, 07:30:31 am »
This iron probably has an internal controller. It may also have a transformer, basic dimmers don't like inductive loads.
 
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Offline Ian.M

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Re: Problem with DIY dimmer
« Reply #2 on: August 19, 2018, 08:12:42 am »
The iron probably has a similar phase control circuit in it for its dual power feature.  As its normal operating power of 20W requires a TRIAC fired at a phase angle of 123 degrees, most or all of the range of your phase control circuit is ineffective.
 

Offline panossTopic starter

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Re: Problem with DIY dimmer
« Reply #3 on: August 19, 2018, 08:24:02 am »
Guys, sorry to dissapoint you...but no internal controller, no transformer, no phase control circuit, no star wars tech.
Take a look at the attached photos (I just opened it up).
A f$$#ing diode in a switch!! :-DD
When the switch is pressed the diode is shorted, so you have the whole sinewave accross the resistor...(and, according to the manufacturer, goes from 20W to 120W... ::))
« Last Edit: August 19, 2018, 08:45:00 am by panoss »
 

Offline Ian.M

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Re: Problem with DIY dimmer
« Reply #4 on: August 19, 2018, 08:40:54 am »
Well, that's unexpected.   The diode can only reduce the power by 50% in any full cycle.   The only way it could work as specified is if they used a PTC heating element, which could draw 120W when cold, but its resistance goes up enough when hot for it to drop to 20W at 50% duty cycle.   In that case, when you reduce power, the element cools and it draws more current till it reaches equilibrium, only slightly cooler.

To be certain what's going on,you'll need to measure the current it takes, preferably using an isolated current probe on a scope.  Alternatively, first measure the element resistance when cold (across mains plug L and N pins with the button held down), run the iron till its at max temperature, unplug it and immediately start measuring its element resistance (across mains plug L and N pins with the button held down), repeating the measurement every ten seconds as it cools till the solder on the bit solidifies.

The diode may be causing issues for your control circuit - You could try putting a 40W incandescent bulb in parallel with the iron so the TRIAC's load isn't Hi-Z on one half cycle, to see if that lets you get a usable control range.

« Last Edit: August 19, 2018, 08:46:37 am by Ian.M »
 

Offline panossTopic starter

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Re: Problem with DIY dimmer
« Reply #5 on: August 19, 2018, 08:52:20 am »
I 'll just replace the diode and the switch with a wire (or short the switch).
But because it must not work at 'full speed' for more than 20 seconds (according to the manufacturer) I 'll always use it in conjuction with my dimmer.
« Last Edit: August 19, 2018, 09:12:10 am by panoss »
 

Offline panossTopic starter

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Re: Problem with DIY dimmer
« Reply #6 on: August 19, 2018, 01:02:15 pm »
What about this:
1. replace the diode in the soldering iron with a wire
2. put the diode 'before' the dimmer (so the circuit is: mains->diode->dimmer-soldering iron)

Should this work?
 

Offline Ian.M

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Re: Problem with DIY dimmer
« Reply #7 on: August 19, 2018, 01:13:30 pm »
Not any better - it doesn't matter what order the dimmer TRIAC, element and switch¦¦diode are, as they are all in a series circuit.

The only good option is to permanently attach its cord to the dimmer.   You can either short out the handle switch and put a 'boost' switch on the dimmer, or rewire with a four wire cord and use the extra wire to make the handle switch the 'boost' switch (which bypasses the dimmer pot so it goes to full power when pressed).   In series with the dimmer pot, put a preset so you can set max normal power to a bit more than 50% - 60% should be OK.

However at the end of the day, its still an unregulated firestick, and you'd have been better off getting a dirt cheap Hakko clone, then saving up to replace the bit and element with genuine parts.
« Last Edit: August 19, 2018, 01:16:19 pm by Ian.M »
 
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Offline panossTopic starter

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Re: Problem with DIY dimmer
« Reply #8 on: August 19, 2018, 02:22:52 pm »
I don't understand why the diode makes it work in 'full mode' no matter the pot 's position.
Can someone explain this?
 

Online Andy Watson

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Re: Problem with DIY dimmer
« Reply #9 on: August 19, 2018, 02:29:27 pm »
It's clearly not a diode. A diode would simply halve the power. Are there any markings on it? Can you provide a close-up, in focus picture of it?

 

Offline panossTopic starter

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Re: Problem with DIY dimmer
« Reply #10 on: August 19, 2018, 02:45:43 pm »
It clearly is a diode, 1N4007.

 

Online Andy Watson

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Re: Problem with DIY dimmer
« Reply #11 on: August 19, 2018, 03:00:02 pm »
There must be some nefarious activity elsewhere then :)

The DC component will alter the response of your phase controller, but that does not explain why it goes to full.

ed: negation added, oops !
« Last Edit: August 19, 2018, 03:15:46 pm by Andy Watson »
 

Offline panossTopic starter

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Re: Problem with DIY dimmer
« Reply #12 on: August 19, 2018, 03:06:25 pm »
but that does explain

Does or does not?
 

Offline schmitt trigger

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Re: Problem with DIY dimmer
« Reply #13 on: August 19, 2018, 03:12:27 pm »
The photo is too blurry to read the part number.

A possibility is that the “diode” is actually a SIDAC?
I used it once as a simple, one step dimmer.
 

Offline panossTopic starter

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Re: Problem with DIY dimmer
« Reply #14 on: August 19, 2018, 03:14:11 pm »
I know that it 's blury but this is because of the camera.
I can see it my own eyes it 's a 1N4007 diode.
« Last Edit: August 19, 2018, 03:25:10 pm by panoss »
 

Offline panossTopic starter

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Re: Problem with DIY dimmer
« Reply #15 on: August 19, 2018, 04:12:34 pm »
I want to make a simulation of my dimmer in LTSpice (for educational purposes, to learn a little bit of LTSpice).

In C:\Program Files\LTC\LTspiceXVII\examples\Educational I found dimmer.asc (I attached it in case you don't have it)

I want to change the Triac to the one I have (BTA12-600B) and the diac to BR-100. (in dimmer.asc I see just 'Triac', something generic and not a specific Triac)
How can I do this?

 

Offline Ian.M

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Re: Problem with DIY dimmer
« Reply #16 on: August 19, 2018, 06:09:22 pm »
You'd need LTspice compatible models for the DIAC and TRIAC you want to use,  put the model files (.sub or .lib) in the same folder as the sim, add a .lib statement to invoke each of them and set the part no.s of the TRIAC and DIAC symbol each to the name of a model in your model files.

P.S. I *strongly* recommend measuring the iron element's hot and cold resistances by the procedure I described in reply#4.  The *ONLY* way that iron can meet its specs for power levels is if the element is a PTC resistance.
 

Offline panossTopic starter

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Re: Problem with DIY dimmer
« Reply #17 on: August 19, 2018, 09:14:38 pm »
Here is what I did yesterday for the diac:
1. I created a file named 'BR100_diac.mod.:
2. I opened it with LTSpice.
3. I added this content (I found it here) and saved it:
Quote
.subckt diacBR100 1 2
*Based on BR100 measured data
*Convergence problems often occur with this model
*If you have a better model please tell me
Vdummy 1 5 dc 0
Ediac 5 2 TABLE {I(Vdummy)} =
+ (-10.06m,-20.46) (-9m,-20.5)    (-7.02m,-20.72) (-5.98m,-20.89)
+ (-5.05m, -21.11) (-3.26m,-21.91) (-2.15m,-22.96) (-1.6m,-23.99)
+ (-7.2n,   -32.5) (-4.0n, -32) (-3.2n,-31) (-2.9n,-30) (-2.5n,-28.03)
+ (-2.3n,-25.27) (-2n,-20.15) (-1.9n,-15) (-1.8n,-7.96) (-1.5n,-1.2)
+ (0,0) (1.6n,1.24) (1.65n,5.15) (1.7n,7.91) (1.8n,10.1) (1.9n,15)
+ (2.1n,20) (2.4n,25.28) (2.9n,28.26) (3.3n,30.5) (1.6m,23.21) (2.3m,22.16)
+ (3.1m,21.44) (4.05m,20.99) (5.01m,20.65) (6.04m,20.32)
+ (6.98m,20.14) (8.09m,20.02) (9.08m,20.02) (10.12m,19.91)
.ends diacBR100
4. Right click->create symbol
5. Component->AutoGenerated->diacBR100 and the part enters in the schematic.

I suppose the procedure is correct, but the model?
How shall I know if it 's correct?

And the model for BTA12-600B? I haven't found anything.
 

Offline panossTopic starter

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Re: Problem with DIY dimmer
« Reply #18 on: August 20, 2018, 07:13:58 am »
I did as suggested:
When cold, Resistance=280 Ohm.
Time(seconds)Resistance(Ohm)
0"1100
10"1014
20"955
30"906
40"860
50"827
60"790
70"745
80"712
90"683
100"660
110"640
120"622
130"605
140"587
150"560
160"546
170"533
180"521
190"505
100"490
210"477
« Last Edit: August 20, 2018, 07:24:55 am by panoss »
 

Offline Ian.M

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Re: Problem with DIY dimmer
« Reply #19 on: August 20, 2018, 08:40:51 am »
Yep. That's a PTC element.  At 230V RMS supply, it will initially run at 189W from cold, dropping to 48W (or maybe 44W if you extrapolate to allow for the time delay from disconnecting till the first resistance reading), so with the diode in circuit that would be 22W, which matches up well enough with the iron's specs.

The DIAC models from users.skynet.be/hugocoolens don't play well with LTspice.   The tabular behavioural voltage source model  is problematic due to all the breakpoints in the curve and because it breaches one of the required assumptions for a BV source:
Quote from: LTspice help
... However, it is assumed that the circuit element current is varying quasi-statically, that is, there is no instantaneous feedback between the current through the referenced device and the behavioural source output. ...
and the macro model isn't in LTspice compatible syntax.   
 
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Offline panossTopic starter

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Re: Problem with DIY dimmer
« Reply #20 on: August 20, 2018, 08:53:22 am »
Yep. That's a PTC element.  At 230V RMS supply, it will initially run at 189W from cold, dropping to 48W (or maybe 44W if you extrapolate to allow for the time delay from disconnecting till the first resistance reading), so with the diode in circuit that would be 22W, which matches up well enough with the iron's specs.
This (pleasantly) surprises me, I expected that the manufacturer would be too...optimistic  ::), as usually happens with these cheap electronics stuff.

The DIAC models from users.skynet.be/hugocoolens don't play well with LTspice.
So, where can I find the correct models for the diac and the triac (BR100 & BTA12-600B)?
 

Offline Ian.M

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Re: Problem with DIY dimmer
« Reply #21 on: August 20, 2018, 09:32:11 am »
Well you can *try* converting the macro model from users.skynet.be/hugocoolens to LTspice syntax:
Code: [Select]
************************************************************************
* BR100: Diac, breakover voltage 32V, breakover current 10uA
* Pkg: Do-35, Ref: Philips, measured I-U characteristic by H. Coolens
* modelled phenomenologically as a current-dependent voltage source
* rise/fall times from parallel capacitance/serial resistance too small!
* BR100 rise time 1.5us typ. (discharge of 100nF with Ipeak=0.5A)
* DB3 rise time 2us max. (10%-90%, discharge of 100nF through 20Ohm)
* author: Detmar Welz
*
* Patched for LTspice syntax, but totally untested
************************************************************************
.subckt BR100 a b params: A=8.5 B=1u C=80m
Vdiac 1 a dc 0 ; ammeter
Cdiac 1 b 1n ; important for stability
Rdiac 1 2 1
Bdiac b 2 v={A}*atan(i(Vdiac)/{B})/i(Vdiac)**{C}
.ends BR100
************************************************************************
but don't blame me if it gives convergence errors or stalls the LTspice engine!  Use with misc\DIAC.asy.

You got lucky - BTA12-600B is in the Triac_st library at LTwiki.org:
http://ltwiki.org/files/LTspiceIV/lib/sym/ValVol/ST/thyristors_st/triac/Triac_st.lib
Download it and use with misc/TRIAC.asy by
Code: [Select]
.lib Triac_st.lib
« Last Edit: August 20, 2018, 09:34:22 am by Ian.M »
 
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Offline Ian.M

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Re: Problem with DIY dimmer
« Reply #22 on: August 20, 2018, 09:46:21 am »
Just a thought - I *think* that iron could be temperature controlled by a smart enough controller.    If you run it from DC, the current through it can be used to calculate the element resistance, which can give you the element temperature, and, if the thermal resistance to the tip can be characterised, the bit temperature could be modelled from the excess power required to maintain the element temperature over that with the iron at rest.

The devil would be in the details - maybe full wave rectify the mains then use a MCU to do fast PWM with a MOSFET, sensing the voltage and element current during the PWM on time.  However the firmware would be non-trivial to write.
 

Offline panossTopic starter

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Re: Problem with DIY dimmer
« Reply #23 on: August 20, 2018, 09:59:20 am »
put the model files (.sub or .lib) in the same folder as the sim, add a .lib statement to invoke each of them and set the part no.s of the TRIAC and DIAC symbol each to the name of a model in your model files.
1. I created a file BR100.sub in the same folder as my .asc file
2. I put as content of BR100.sub the text you posted.
3 . I put op: .inc F:\LtSpiceProjects\dimmer_1\BR100.sub  (in folder F:\LtSpiceProjects\dimmer_1 are located the dimmer_1.asc and the BR100.sub files)
4. I don 't understand what you mean by 'set the part no.s', can you explain a bit more?

What I also did:
I put a generic diac, the one included in LTSpice, right clicked it and as 'SpiceModel' I entered 'BR100'. Is this correct?

Just a thought - I *think* that iron could be temperature controlled by a smart enough controller.    If you run it from DC, the current through it can be used to calculate the element resistance, which can give you the element temperature, and, if the thermal resistance to the tip can be characterised, the bit temperature could be modelled from the excess power required to maintain the element temperature over that with the iron at rest.

The devil would be in the details - maybe full wave rectify the mains then use a MCU to do fast PWM with a MOSFET, sensing the voltage and element current during the PWM on time.  However the firmware would be non-trivial to write.
Sounds very interesting.
But I would need a rather hard to find PSU, an SMPS that would convert 230VAC to 230VDC...(30 Watts??)
« Last Edit: August 20, 2018, 10:14:10 am by panoss »
 

Offline Ian.M

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Re: Problem with DIY dimmer
« Reply #24 on: August 20, 2018, 10:34:58 am »
Place a DIAC (misc\DIAC.asy) and right click its attribute:value which is initially 'DIAC' and change it to 'BR100'.

If the model file is in the same folder as the sim, you don't need the full path in a .inc or .lib statement, so chop that down to:
Code: [Select]
.inc BR100.sub
For the DC supply, if the controller is measuring both the voltage and the current, simply full wave rectify the mains and *DON'T* use a reservoir capacitor.  The resulting waveform peaks at 325V (assuming 230V mains) but the RMS voltage is only 230V.   Use a separate supply for the MCU e.g. the board from a basic USB charger wallwart.

PWM the full wave DC at lets say 31KHz with 50% duty cycle, and you'll have the same power level as the switched diode gave.   Ideally the PWM should be just above the audio frequency range, but if you don't mind the risk of it 'singing' a bit, a lower PWM frequency could be used - which will be necessary if the MCU's ADC isn't fast enough to take at least two samples during the PWM period, one for voltage and the other for current.
 


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