No, I don't want to make my fan go dark, just control its speed!
240v AC, a few 10s of watts, classic induction motor I suppose.
Are there special triac circuits for inductive loads like this or can a standard one (ie filament lamp dimmer) be used?
The only one I have to hand is potted so I cannot see the circuit, and marked "not for inductive loads"
(It does say "Anything Else" at the top
TIA
Cliff
240v AC, a few 10s of watts, classic induction motor I suppose.
Are there special triac circuits for inductive loads like this or can a standard one (ie filament lamp dimmer) be used?
The only one I have to hand is potted so I cannot see the circuit, and marked "not for inductive loads"
(It does say "Anything Else" at the top
TIA
Cliff
I spend most of my work day working with (mostly) leading edge dimmers and I'm not aware of any standard type dimmer being made in the lighting industry for inductive loads.
I have seen it done with small motors but you do run the risk of cooking the dimmer, perhaps spectacularly. Standard dimmers tend to cut the AC sine wave pretty nastily too , I can't see that being good for the motor. The cheaper the dimmer the quicker the rise time - or harshness of the cut, if you like, that's why you find cheap dimmers kill light bulbs more quickly.
You might find something triac or SCR based made specifically for inductive loads but I'm not aware of anything made for lighting that could be used for both. Or at least, not reliably.
Hope that helps
Peter.
I have seen it done with small motors but you do run the risk of cooking the dimmer, perhaps spectacularly. Standard dimmers tend to cut the AC sine wave pretty nastily too , I can't see that being good for the motor. The cheaper the dimmer the quicker the rise time - or harshness of the cut, if you like, that's why you find cheap dimmers kill light bulbs more quickly.
You might find something triac or SCR based made specifically for inductive loads but I'm not aware of anything made for lighting that could be used for both. Or at least, not reliably.
Hope that helps
Peter.
Thanks for replying, BUT
The previous owner fitted a speed control to my kitchen cooker hood!
The motor is a 230V caged induction motor (I assume it is - no cap or brushes) and the speed controller is in a standard lighting patress, with a fan symbol on the control knob.
It works fine fron almost idling to full speed - unfortunately the innards are potted in black gunk so I cannot find out the circuit without destroying it!
I am not to sure about your statement on "cut sine-waves".
All the lamp dimmers I have seen use a simple phase-angle (R-C-diac) fired triac with no attempt at slope tuning.
The previous owner fitted a speed control to my kitchen cooker hood!
The motor is a 230V caged induction motor (I assume it is - no cap or brushes) and the speed controller is in a standard lighting patress, with a fan symbol on the control knob.
It works fine fron almost idling to full speed - unfortunately the innards are potted in black gunk so I cannot find out the circuit without destroying it!
I am not to sure about your statement on "cut sine-waves".
All the lamp dimmers I have seen use a simple phase-angle (R-C-diac) fired triac with no attempt at slope tuning.
I have seen ceiling fans that change speed with a "dimmer" but i do not think they are the same thing as a light.
The light just gets a bit l of the current cycle turned off by a triac. but most fans use a synchronous motor (AC brushless) ithink it might get a bit slower and then just stop. (if the inductance of the motor did not kill it first)
240V cieling fan controller might be available in warmer countries that use 240v?
The light just gets a bit l of the current cycle turned off by a triac. but most fans use a synchronous motor (AC brushless) ithink it might get a bit slower and then just stop. (if the inductance of the motor did not kill it first)
240V cieling fan controller might be available in warmer countries that use 240v?
A little more info..........
http://www.fairchildsemi.com/an/AN/AN-7511.pdf
Chapter 3 in this text....
http://www.nxp.com/acrobat_download/applicationnotes/APPCHP3.pdf
Looks to be a Triac AC motor control....
http://www.spelektroniikka.fi/kuvat/triacd.pdf
I hope this helps!
Tall Shadow
http://www.fairchildsemi.com/an/AN/AN-7511.pdf
Chapter 3 in this text....
http://www.nxp.com/acrobat_download/applicationnotes/APPCHP3.pdf
Looks to be a Triac AC motor control....
http://www.spelektroniikka.fi/kuvat/triacd.pdf
I hope this helps!
Tall Shadow
Tall Shadow said:
Thanks again!
The third item is interesting (the first two deal with PWM control).
Is that Hungarian or Finish?
Anyway, the chip used (U208B) has a Telefunken data sheet showing this circuit and clearly states:
Because the current lags the voltage with inductive (motor) loads, there is a built-in current detector which prevents false triggering when the load current is > 0.
I don't find any of this very intuitive - a life-long fear of coils etc!
Anyway, thanks for your help!
agm2003 said:
Well, as we have seen from above, the problem is phase chopping an INDUCTIVE load with a "conventional" TRIAC dimmer.
Since the current lags the voltage, it is necessary for the control circuit to have a current sensor so that switching does not take place in those quadrants where I > 0.
When I have time I'll get the 'scope out to better understand how that works. It DOES work!
agm2003 said:
cliff said:
Here in the States, in the "Home Improvement" stores I mentioned, They sell Ceiling fan Speed controls that are made just for controlling the motor's speed. They are not just a "Lamp Dimmer" or other simple Triac chopper controllers. They are purpose built just for fan speed control.
I know your electrical system is 220vac -vs- our 110vac, but there has to be someone over there who uses an AC speed controller in something that you can adapt.
Look around at various places where AC motors are used..then see if you can adapt the controllers to your usage.
Maybe you could even find what you are looking for at a surplus shop???
I'm just thinking "Out Loud" here.....
Tall Shadow
I don't have enough time at the moment to read all the replies but I have looked at triac phase fired controllers before and whenever you connect the triac to a load with significant inductance you have to be careful that the phase difference between the current and voltage doesn't latch the triac. It's normal to fit snubber circuits at the output to avoid that - but you can also buy 'snubberless' triacs, I think ST Microelectronics make some. And like the others say, noise.
I vote variac.
I vote variac.
This thread has wandered off!
You are correct, except that a variac is not possible in a domestic situation!
The links posted by Tall Shadow earlier show that the problem (out of phase current) can be solved by sensing both voltage and load current to compute the correct firing time. Thee are chips that do this.
Really, there is not much more to say.
eeka chu said:I don't have enough time at the moment to read all the replies but I have looked at triac phase fired controllers before and whenever you connect the triac to a load with significant inductance you have to be careful that the phase difference between the current and voltage doesn't latch the triac. It's normal to fit snubber circuits at the output to avoid that - but you can also buy 'snubberless' triacs, I think ST Microelectronics make some. And like the others say, noise.
I vote variac.
You are correct, except that a variac is not possible in a domestic situation!
The links posted by Tall Shadow earlier show that the problem (out of phase current) can be solved by sensing both voltage and load current to compute the correct firing time. Thee are chips that do this.
Really, there is not much more to say.
I have used the ceiling fan type to control other fans, worked a treat! But I do admit, never saw one in Europe or the UK. Here in the States they are very common.
Gajanan's comment about the resistor/capacitor controller is interesting. I remember years ago seeing a dimmer project in an electronic mag that used caps to dim a light. The idea was to NOT generate noise.
It used different cap values switched into the circuit in series with the lamp. Just a 1st order low pass filter!
Gajanan's comment about the resistor/capacitor controller is interesting. I remember years ago seeing a dimmer project in an electronic mag that used caps to dim a light. The idea was to NOT generate noise.
It used different cap values switched into the circuit in series with the lamp. Just a 1st order low pass filter!
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