AC Soft Start Incandescent Lamp switch (*FINAL EXPERIMENTAL RESULTS*)

[hgg]

Hi,

In my opinion the best artificial lighting available in the 21 century is still the humble incandescent lamp
for many reasons.  The only problem is that apart from the fact that they are slowly becoming extinct,
after the introduction of the toxic "energy saving" bulbs, the lifetime of the incandescent ones for some
strange reason started to decline dramatically.  <-- (conspiracy theory)   

So, you are replacing the lamps more often than before.   They main thing that burns the incandescent
bulbs is inrush current.  When cold they have low resistance and the sudden increase in voltage creates
very large currents which raise the temperature of the filament very fast.  That is why they get burned
only when they are switched on.  I always wanted to build a small circuit that will switch them on slowly. 
I've searched the net and I could not find any circuit. Only thing I found was the strange Russian guy in
youtube advertising a similar circuit and calling it a phase controller.  (don't know why)

Do you think that something like the following will work, or will it explode?..   


AC Soft Start

Any ideas on a circuit that will actually work?
Thank you!

[Rufus]

They main thing that burns the incandescent bulbs is inrush current.

It isn't the main thing. Lamps have a limited life, when they are almost dead they will likely fail at switch on. Reducing the switch on surge still leaves you with an almost dead lamp that will soon fail anyway.

[hgg]

I would have to disagree with you.
The "limited lifetime" is created by the extreme thermal stress upon switching on
and their actual lifetime is greatly reduced when used is such a way.

[Rufus]

I would have to disagree with you.
The "limited lifetime" is created by the extreme thermal stress upon switching on
and their actual lifetime is greatly reduced when used is such a way.

This http://donklipstein.com/bulb1.html provides a quite good explanation of why you would have to be wrong.

[hgg]

From the same reference:

Making bulbs last longer:
  Long-life bulbs
  Reduced Power
  Soft-start devices ...

Anyway, that was not my initial question. 
If you know how to make a simple circuit that will slowly turn on a bulb please share it.
(Or if you think that the one I've posted will work or not.)

Thank you.

[Paul Moir]

That will not work, but it won't explode.  At 50Hz you could replace that capacitor with a wire and it would make no real difference.  Also 1000uF non polarized capacitors are hard to come by.

NTC thermistor seems like the easier way to do it. 

[hgg]

Hello Paul,

Do you mean using an NTC thermistor in series with the bulb?
What about an AC to DC converter which will power a circuit that will switch on slowly the TRIAC?

An even better idea might be to combine a soft start/stop circuit with a current limiting circuit so
that you will be able to use a 100W bulb, that has a thicker filament, light up as a 60W bulb.

[SeanB]

I just use a NTC thermistor ( taken out of a dead PC power supply so likely to be an easy to find part) in series with the lamp. Increases the life from weeks ( frequent switching cycle) to months, often years. green blob on 2 leads in series with the one mains lead, not much simpler than that.

Years ago I built a soft start for a plate exposer, which used 40 40W golf ball lamps as a light source, and which had the unfortunate tendency to trip the 25A breaker at switch on. It used a simple zero cross detector to control the charging of a capacitor which controlled the on time of an unijunction transistor to give a slow ramp up from a low phase angle to max, over a period of around 2 seconds. was very reliable while we had the developer, never had to change a lamp in it after doing this mod to it.

I used the same circuit later on with larger capacitor values to give a 2 minute turn on time to a lamp to gently wake me in winter.

[hgg]

SeanB, too much for me to digest in a single paragraph...   
That sounds exactly what I want, but the unijuction transistor, I hear it for the first time ...
I will look it up.  Do you have any circuit diagram to have a look at?

So the NTC thermistor is a good solution, but if I can make it ramp up in 30 seconds it would
be even better.  What about the slow switching off?  It might not affect the filament as much but
it will make a difference as well. 

Thank you!

[hgg]

What about the following circuit modification?


AC Soft Start 2

If I find a way to slowly power the gate of the TRIAC, wouldn't that cause the bulb to light up slowly;
Maybe the capacitor needs to be in series with the gate of the TRIAC. (?)

[Zero999]

Just buy a dimmer switch. The amount of time for you to turn the it on should be sufficient to act as a soft start to lengthen the life of the bulb.

[hgg]

Hero999,

Indeed I can buy the dimmer, or even the soft starter circuit already assembled, (if I can find it),
but I also want to learn a thing or two by building it myself.

[Kjelt]

If you insist using incandescent lamps why not switch to 12V Halogen. If you run them with a modern SMPS at 11,7V they have a very long lifetime and the SMPS does the softstart for you. Cheap, long lifetime, no problem but also no project.

[SeanB]

Unijunction transistors are now pretty much unobtanium devices, so building it will be difficult. NTc is cheap and simple, so I use it.

[hgg]

Kjelt the 12V halogen lamps would need transformers and would be difficult to use them on ceiling
lighting.

SeanB, do you know what the switch on time would be with an NTC thermistor?
Can I change that with different thermistors?

(I've already found one from a faulty power supply I had.   Its an SCK2R58)

[IanB]

The modern world is making it very difficult to have controllable lighting. Every light in my house is on a dimmer switch, and I run all my lights at 1/3 to 1/2 brightness. Putting the lights on full power now results in an "Ow! My eyes!" level of brightness.

Sadly, CFLs are invariably not dimmable (and the light has a horrible colour). LED lamps are sometimes dimmable, mostly not, but are hugely expensive. The halogen replacements for regular incan bulbs are not dimmable either. Halogen lamps need to be run at near full power to work properly. I have read that if you dim them they will have a shorter lifetime.

Fortunately I have found that bulbs run at half brightness last for years, so I can stockpile spare bulbs.

[edavid]

The modern world is making it very difficult to have controllable lighting. Every light in my house is on a dimmer switch, and I run all my lights at 1/3 to 1/2 brightness. Putting the lights on full power now results in an "Ow! My eyes!" level of brightness.

Why don't you buy lower wattage bulbs?

Sadly, CFLs are invariably not dimmable (and the light has a horrible colour). LED lamps are sometimes dimmable, mostly not, but are hugely expensive. The halogen replacements for regular incan bulbs are not dimmable either. Halogen lamps need to be run at near full power to work properly. I have read that if you dim them they will have a shorter lifetime.

This is old data, dimmable CFLs are readily available (although expensive).  Also, you have your choice of color/colour temperature.  Warm white CFLs are very close to incandescent.

[hgg]

IanB that's what I want to do.  Run higher wattage bulbs at lower brightness and also use the
soft on - soft off circuit.  I think that they will last much longer this way.

[edavid]

Anyway, that was not my initial question. 
If you know how to make a simple circuit that will slowly turn on a bulb please share it.
(Or if you think that the one I've posted will work or not.)

Well, it was the premise of your question.  If you start from a faulty premise, you can't expect people to ignore that.

Anyway, your circuit won't work.  You need to PWM the bulb from 0% to 100% over the desired startup time.  Your circuit has no way to do that, it's just a dimmer.

The NTC method is the only simple way to do it, but it has the flaw that if you turn the lamp off and then on again, the thermistor stays hot, so it doesn't do anything.  Maybe that doesn't matter since it's a placebo circuit anyway.

[IanB]

Why don't you buy lower wattage bulbs?

Most are 40 W or 25 W.

This is old data, dimmable CFLs are readily available (although expensive).

Why should I replace inexpensive incandescent bulbs with expensive CFLs?

Also, you have your choice of color/colour temperature.  Warm white CFLs are very close to incandescent.

I have not yet met a fluorescent lamp with a pleasant colour. (Also dimmed incans have a warm yellow glow similar to firelight.)

[edavid]

Why don't you buy lower wattage bulbs?

Most are 40 W or 25 W.

Then 15W bulbs should be perfect.

Why should I replace inexpensive incandescent bulbs with expensive CFLs?

I didn't say you should - just that your statement that CFLs are "invariably not dimmable" is incorrect.

I have not yet met a fluorescent lamp with a pleasant colour. (Also dimmed incans have a warm yellow glow similar to firelight.)

It sounds like the problem is that you don't like 2700K "warm white" light.  You must  really hate daylight.

[IanB]

I have not seen a dimmable CFL on the shelves of any brick and mortar store, ever. Believe me, I look every time I go past the lighting section. Where are the dimmable ones to be found?

[Kjelt]

The modern world is making it very difficult to have controllable lighting.

The modern world is making it extremely easy to have controllable lighting, DALI, DMX, Zigbee, Zwave, Dynet, IP, 0-10V, you name it there are lighting fixtures that support it and controllers that make the entire home controllable in a snap.

LED lamps are sometimes dimmable, mostly not, but are hugely expensive.

What is expensive? It is so relative. People spent fortunes on their interior: tables, closets, couches, paintings but lighting which is equally as important to make those couches and paintings etc. shine and flourish at evening to enjoy, may not cost anything? Weird world.

This is old data, dimmable CFLs are readily available

True, but they are being replaced with leds if quality of lighting is an issue.
CFL's and TL's do have a small dimming problem:
1) The colourtemperature rises when dimming, so in contrary to a lightbulb where the colortemperature lowers when dimming the CFL white gets colder. This is due to the phosphors.
2) When dimming, the current through the tube is lowered, but the temperature must not get under a certain temperature or the current will stop and the light is out. Therefore the current through the filaments is increased when dimmed and in case of extreme dimming (<10%) the lifetime of the lamp decreases rapidly.

Anyway here in northern Europe everyone is already starting to switch to Leds, my new extension of the livingroom was fully led and I built my own RS485 network and drivers to control them.

[hgg]

eDavid,  Where is the faulty premise?

They main thing that burns the incandescent bulbs is inrush current.  When cold they have low
resistance and the sudden increase in voltage creates very large currents which raise the temperature of
the filament very fast.

Do you have any actual data which show that inrush current and thermal stress are not important factors
for the lifetime of incandescent lightbulbs?  If you have, you would save me time trying to build this circuit.

[SeanB]

Around a second, plenty of time for the lamp to warm up to operating temp. You typically have an inrush of around 10x normal, which is a lot better than the typical 50x of a cold lamp. Basically it is a 5R or 10R series resistor to limit current in the initial stages to keep the rate of heating down.