TRIAC Dimmer

Who says that they do? News to me. They sould extend bulb life anyway.

Do you have a source for that assertion ? Doesn't sound right to me.

Not if used to control the load the same way ( phase control ). IGBTs and MOSFETS are being used for pwm control though which also gets over the lamp 'singing' issue.

Graham.

Luhan Monat wrote in news:FPqke.1049$rr.824@fed1read01:

They sure extended the life of the 130VAC bulb in my dining room;it lasted

Of course,lamps are resistive loads while motors are inductive loads.

I never heard of any IGBT or Power MOSFET dimmer for consumer use.

Hi all,

Quote:

Power harmonics caused by dimmers

All phase control dimmers are non-linear loads. A non-linear load is one where current is not in proportion to voltage. The non-linear load on dimming systems is caused by the fact that current is switched on for only part of the line cycle by a phase control dimming system. This non-linear load creates harmonic distortion on the service feeder.

Harmonics are currents that occur at multiples of the power line voltage frequency. In Europe where line frequency is 50 Hz the 2nd harmonic frequency is 100 Hz; the 3rd harmonic is 150 Hz, and so on. In North America where line frequency is 60 Hz the 2nd harmonic frequency is 120 Hz; the 3rd harmonic is 180 Hz, and so on.

Excess harmonic currents cause conductors and the steel cores of transformers and motors to heat. Odd-order harmonic currents (specifically the 3rd harmonic) add together in the neutral conductor of 3 phase power distribution systems. The 3rd order harmonic current present on the neutral is the arithmetic sum of the harmonic current present on the three phase conductors (this also applies to the 9th, the 15th and so on harmonics). Harmonics could theoretically elevate the neutral current to 3.0 times what is present on a phase conductor. With typical phase control dimming system connected to three pahse feed, the harmonics normally elevate neutral current to about 1.37 times phase current. If the wires are not properly rated for this, neutral conductor overheating or unexplained voltage drops can occur in large dimming systems.

Please see this

Hi, Jack. In addition to the other good concepts already mentioned, you also might want to look at the DC component of the motor voltage. A simple lamp dimmer (pot+R/C, diac, triac with R/C snubber across the triac and series choke to limit EMI) usually doesn't switch symmetrically around the AC neutral, because of breakover voltage asymetry in the diac. That results in a DC component being applied to the motor of up to several volts, which causes heating and reduces life.

Good luck Chris

Hi Chris,

Thanks for your suggestion. I was curious because a simple triac dimmer as you suggested is causing lot of heating in my induction motor, particularly at low speed. So I thought to figure out the problem before I use it in a microcontroller driven dimmer, where I'll be using triac driver MOC3022, which would probably don't cause any DC component problem.

Thanks

They don't. However, if you adjust a motor controller to the point that the motor stalls, that could bring about the motor's demise. It is not the triac that causes the problem, it is the misuse of allowing the motor to stall.

Will an IGBT or Power MOSFET dimmer provide a

Since the triac does not cause the problem, the question is moot.

Ed

The problem is trying to use a triac dimmer on an induction motor.

For an induction motor, you need a completely different approach, maybe even a different kind of motor.

Sorry I don't have any suggestions as to how to go about fixing the problem, maybe google on "induction motor speed control".

Good Luck! Rich

Right, the PIC folks are fond of pushing their dsp chips as a solution to this problem. They use the dsp and power drivers to generate a very high current, variable frequency sine wave at 12V, and then push it through a transformer to power the induction motor.