[SirAlec]

^^^
that was my next exact query.

[meerkat]

Originally Posted by wildon

The problem may be because of the Bulb wattage. Normally fan regulators made for controlling low wattage (75W). If you are using a 100W bulb it may burst

Try connecting a lower watt bulb 40w or 60 w and see.

I am using a 40w or 60 w bulb.

Why would a 100w bulb "burst"? If the regulator is not designed
to handle such higher wattage, shouldn't that itself burn?

[meerkat]

Originally Posted by govigov

if you are not using the regualtor switch, i would suggest by passing the regulator and connect the lamp directly to the switch.

007 has already asked this, and I've answered.

The question at hand is why the problem is occuring, -- not how to solve it.
Just wanted to learn something.

[amitk26]

Originally Posted by meerkat

This is a decidedly low-tech puzzle. But, here goes ...

Well it looks low tech but it is not Also this is a power electronics puzzel, I will try to answer based on my rusty knowledge of electronics as I am not a practicing electronics person any more.

The modern fan regulator circut uses a Silicon Controlled Ractifier, SCR is a device which fires at a perticular angle based on the gate trigger current which is set by the knob you rotate the output is not a pure sine wave but truncated sign wave and trucated portion depends on the firining angle set so while this is not an issue in case of an inductive device like motor ( Don't ask me how but as of now just note that a large inductance and a capacitor can smoothen the harmonics , This is also known as dampning) it damages a bulb filament becuase there it can not handle the harmonics.

In case of normal SCR used in Fan regulaor circuit , The values are not very precise and I suspect in the case of knob turned full also it is not a pure sinewave and there are some harmonics. As bulb filament ages it's capability to handle the surge reduces and it burns out.

To explain in simple words just try to remember how a pure sine wave looks like it is some thing like ~ so the volage rises from 0 to Max and then 0 to min at 50Hz that is 50 times in a second. The volatage rating you see is a Root mean square ( RMS) value. Now with an SCR acting as controller some portion of this wave is chopped off when the gate is closed thus RMS current value is reduced but the chopped wave result in harmonic freqencies which can add up and give higher peaks when the harmonics are in phase.

The purpose of a regulator is to limit current traditionally regulators were resistances which meant that there was lot of power wasted in generated heat. The same effect was achived using an SCR and here no current flows for a portion of cycle thus no loss .

[ajith]

Am not an electrical or electronic engineer but this is what i think is going on. Most of these fan speed regulators nowadays are electronic and work on the principle of wave chopping. They slice the AC wave down to reduce the overall power being put into the device. (Hence the odd hum from the fan at low settings.) If that is the case, the surge is likely an overvoltage spike caused by a capacitor discharge in the device sending the voltage well above the safe limits for the filament. Copper wires are a little more tolerant of spikes. Also would explain why the MCB trips. Ideally, they ought not to do that. Sounds like a faulty unit to me.

I would suggest you simply ignore the switch and use the dimmer for controlling the lamp. Since you will be switching it on at low and then sweeping up to high, the output voltages will be too low to cause problems.

[siddartha]

meerkat - a fan regulator whether it a new type or old type is called a fan regulator for a reason.

so as a light dimmer is called a dimmer for a reason.

as mentioned before the two are different.

i suggest you try using a dimmer instead of fan regulator.

the wattage of the bulb has no bearing here.

[amitk26]

Originally Posted by siddartha

i suggest you try using a dimmer instead of fan regulator.

the wattage of the bulb has no bearing here.

To convert a new type of regulator to dimmer just add inductance for dampning that is a lot of copper wire wound on a ferrite rod.

In other words lamp dimmer is similar just little costlier for the reason above.

[greenhorn]

I've been using a fan regulator to control a pair of 40W bulbs in our house. they've been running for several years now, no issues.

Are you sure the regulator is fully functional?

[dinar]

The newer regulators for fans are electronics, SCR based and are designed for a inductive load [motor], unlike the resistive load your adding [bulb]. The inductive load need a capacitive Impedance matching to get a proper power factor or else the electric Bill will go off the roof.
the older regulators were resistive based and would work fine with any sort of load as it could absorb most of the power and heat up.
The new regulators work on the bases of regulating the actual wave[chopping the wave] so there is always a small amount for electrical noise in the AC wave which the bulb coil can not handle,hence the bulb blows.
As for the bulb blowing after certain time, there is a certain amount of surge handling capabilities built into the bulb, but the surge happening on regular bases cause the tungsten coil fatigue.
Just disconnect the regulator and use the switch your done

[meerkat]

Thanks guys, for all your responses.

amitk26, ajith, dinar, -- your explanations seem to be the most plausible. Thanks.

greenhorn, that's intriguing. What kind of regulators are you using? As I've
said, my experience is same with two distinct regulators (new), -- I think it's
unlikely that both are bad units.

[sandeepmdas]

My knowledge is limited and outdated in this field, but I think both the light dimmer and the modular fan regulator use Triac-based circuits.

[amitk26]

Originally Posted by sandeepmdas

My knowledge is limited and outdated in this field, but I think both the light dimmer and the modular fan regulator use Triac-based circuits.

Yes Triac is a bidirectional device which can chop off the wave in both directions but the explanation of harmonics generation and firing angle based on gate trigger is same in case of SCR or Triac.

Triac is more suitable for AC circuitcs I have totally forgotten now in what cases SCR bridge was used and where Triacs were preferred.

[shyamhegde]

Did you try only using the regulator to switch the bulb on and off instead of the 'fan Switch` as you mentioned? a bouncing switch contact also could be a reason.
I had used a normal fan regulator as dimmer for a 60watts bulb and it ran fine for years (we changed the house and do not know how it is now).

This looks to be either bad wiring or switch causing problem - similar to our cars, which causes the headlight bulbs to fuse, due to bas install during bulb power upgrade.

[Fillmore]

I have the same setup for 2 sets of fancy lights.
Its been over 2yrs now. No problem what so ever.

I connected a fan regulator in place of the normal switch, works fine.

[clevermax]

I presume that you are using an electronic regulator.

When you turn on the knob, and until you turn it to max, the sinusoidal wave form gets clipped - the angle of clip gets changed as you turn - this is how the electronic regulators regulate power. You can even hear the humming from ceiling fans operating through this kind of regulators.

Some regulators are really bad that they will go kaput when you use power from an inverter (square waves). I had 4 of them blown in my house wiring and nowadays I stopped using fans when the power is from the inverter.

I think you are using a low quality dimmer (regulator) and it might be sending an initial spike at very high voltage when you are turning it on.
You should first change your regulator to a good quality one and see if that can save the life of the bulb connected through it.