Burn out 120V lamp on 120V circuit?
in [Design]
|
Prev: Project for New American Unix, Physics, Electronics, Metalworking - TUTORIAL VIDEOS
Next: H Bridge, NMOS AND PMOS DRIVER
From: markp on 10 Aug 2010 04:40 "Jim Thompson" <To-Email-Use-The-Envelope-Icon(a)On-My-Web-Site.com> wrote in message news:f4b16699qk6hi6u4lpthe7acbgi2j1r8ke(a)4ax.com... > On Mon, 09 Aug 2010 18:12:40 -0700, VWWall <vwall(a)large.invalid> > wrote: > [snip] > > A lab-tested Spice model for a lamp... > > **** > ** AIRCRAFT LAMP SUBCIRCUIT > *VO=NOMINAL OPERATING VOLTAGE > *IO=NOMINAL STEADY STATE OPERATING CURRENT > *RCOLD=FILAMEMT RESISTANCE MEASURED AT ROOM TEMP (300K) > *TAU=CURRENT TIME CONSTANT AFTER A 0 (zero) TO VO STEP IS APPLIED > .SUBCKT LAMP 1 2 PARAMS: VO=28 IO=25m RCOLD=112 TAU=22m TAMB=300 > H1 6 0 VML 1 > RH1 6 0 1 > GP 0 4 VALUE={V(6)*V(1,2)} > *V(4,0) = FILAMENT TEMPERATURE IN KELVINS > RT 4 5 {300*(VO-IO*RCOLD)/(IO*IO*VO*RCOLD)} > CT 4 5 {TAU*IO*IO*VO*RCOLD/(300*(VO-IO*RCOLD))} > VAMB 5 0 {TAMB} > El 7 0 1 2 300 > R1 7 0 1 > E2 8 0 VALUE={V(4)*RCOLD} > R2 8 0 1 > E3 10 0 7 9 10MEG > R3 10 0 1 > E4 9 0 VALUE={V(8)*V(10)} > R4 9 0 1 > GR 1 3 10 2 1 > VML 3 2 0 > .ENDS LAMP > **** > > ...Jim Thompson Thanks Jim, I'll add this to my library. Mark.
From: markp on 10 Aug 2010 06:02 "VWWall" <vwall(a)large.invalid> wrote in message news:asidnUwFy5bEOv3RnZ2dnUVZ_jSdnZ2d(a)earthlink.com... > markp wrote: >> "Paul E. Schoen" <paul(a)pstech-inc.com> wrote in message >> news:O8%7o.60837$lS1.14657(a)newsfe12.iad... >>> "Sylvia Else" <sylvia(a)not.here.invalid> wrote in message >>> news:8c6oelFig4U1(a)mid.individual.net... >>>> On 6/08/2010 4:03 AM, VWWall wrote: >>>>> A while back, in another Usenet ng, someone asked about using an >>>>> ordinary 120V incandescent lamp to slow down a fan motor. A number of >>>>> posters replied that they had successfully done this. The usual >>>>> discussion of the merits of doing this ensued. >>>>> >>>>> Then, one frequent poster replied that he had tried this with a small >>>>> AC >>>>> motor, and the 120V bulb, in series with the motor, burned out when >>>>> the >>>>> circuit was completed. >>>>> >>>>> There was much discussion, with many saying that it was impossible for >>>>> any two terminal passive device in series with a 120V incandescent >>>>> bulb >>>>> on a 120V circuit to cause that bulb to burn out. >>>>> >>>>> Some even set up Spice simulations which were difficult because of the >>>>> large variation in the bulb's resistance from cold to fully "on". The >>>>> OP >>>>> was asked to repeat the experiment, which he did several times, with >>>>> the >>>>> same results of the bulb burning out. >>>>> >>>>> The final conclusion, perhaps not shared by all, was that it was >>>>> possible for a passive device to act in this way. One poster even >>>>> showed >>>>> Spice results with an increase in line current due to motor >>>>> inductance. >>>>> It was never proved that this increase was enough to cause the bulb to >>>>> fail. >>>>> >>>>> I haven't tried the experiment myself, since I don't have a suitable >>>>> small motor available, and with 120V incandescent bulbs on the >>>>> endangered species list, I don't care to sacrifice even one! Some time >>>>> ago, I did use a series 120V 100W bulb to slow down the compressor fan >>>>> motor in my refrigerator, when the proper replacement was not >>>>> available. >>>>> >>>>> I have my own theory and can postulate a two terminal passive device >>>>> capable of behaving in this way. (It doesn't even need pre-"charged" >>>>> condensers.) >>>>> >>>>> What say ye all? >>>>> >>>> When the circuit's turned on the bulb filament has a lowish resistance, >>>> so a large current can build up in the inductance of the motor. Then >>>> the filament heats up, its resistance increases, and the inductor >>>> pushes the voltage up to keep the initial current flowing, with the >>>> result that the bulb filament has to handle an overcurrent for a >>>> period. >>>> >>>> Whether this will destroy the bulb would depend critically on the >>>> characterstics of the filament and the size of the inductor. >>>> >>>> So I'd have thought that the answer was that it's possible, but actual >>>> mileage will vary. >>> That is food for thought (and thanks for replying on topic instead of >>> getting into politics). >>> >>> I don't think a very large current would build up in the motor, >>> especially a small fan motor which is relatively self-limiting even with >>> locked rotor. If the motor stalls, then the maximum current would be >>> initially limited by the bulb cold filamant resistance, and the locked >>> rotor characteristics of the motor. At worst it would be about the same >>> as connecting the bulb to the line through a short, and since this is AC >>> there is not a constant build-up of inductive energy. If the motor runs, >>> then there may be some energy build up from the flywheel action of the >>> load, but this would build very slowly in comparison to the heating of >>> the filamant and eventual stabilization at a lower speed. The motor >>> itself should only be able to generate the same amount of power that is >>> involved in running at full load, which should be less than 1/8 HP or >>> less than the 100W rating of the bulb. So even flywheel action should >>> not be able to account for enough power being pumped into the bulb to >>> blow it out, especially at turn-on. >>> >>> Paul >> >> I think it is actually due to the inductor slowing the rate of change of >> current down. >> >> I'm going to assume a simple inductor here, not a fan. >> >> If you had just a bulb you'd get a high current initially and it will >> rapidly fall to steady state. So there's a peak power at the beginning >> but only for a very short time, this energy is absorbed easily by the >> element due to it's thermal heat capacity. >> >> When you add an inductor the whole thing slows down, and instead of >> starting at peak power it starts at zero power. It still reaches the same >> steady state condition (no more rate of change of current = 0V across the >> inductor), but because things have slowed down by the inductor, the heat >> capacity doesn't come into play anymore (it already absorbed the heat >> early on), so there'll be a maximum steady state power that the bulb >> could handle before blowing and this is much lower than the normal peak >> power with no inductor. >> > If this were true powering an incandescent bulb from a Variac or other > variable voltage source would result in the bulb's failure before its > rated voltage was reached. Photo-flood lamps are over voltaged, so it > takes quite a bit of excess voltage to instantly fail the lamp. Ah, yes. That probably is not it then. > >> This steady state maximum could, for example, be 90W for a 60W bulb.The >> question is therefore whether the product of the voltage and current >> through the bulb, i.e. the power, would ever rise above this value before >> falling back down to steady state. If it does peak like that then the >> bulb could blow before steady state is reached. >> >> I've no idea what would really happen, but my gut feel is that the power >> curve could have some 2nd order, or even 3rd order, terms in it and may >> well have a maximum. >> >> BTW I found this model of a tungsten lamp in case anyone wants to have a >> go at converting it to LTspice and simulating it: >> www.intusoft.com/nlpdf/nl11.pdf >> > A couple of people have tried modeling the bulb in series with an > inductance. The current does rise above the expected, but not enough to > fail the bulb. > > Paul Hovnanian was on the right track. It's possible to conceive a two > terminal device which could behave in this manner, but it would involve > the storage of energy and the release of that energy in a way that would > over-voltage the bulb. Any ways I could conceive involved some sort of > switch, operated at a precise time. > > A hint: The motor which consistently failed the bulb was a small > capacitor start device. My theory may be wrong. > > -- > Virg Wall Do you know of the exact motor construction that was used? There may be a power factor issue here too, espcially if it was a switched capacitor type where the power factor could change rapidly. Jim has kindly posted a lamp model, what we really need is a motor model with the same construction as the fan. Anyone got one? Mark.
From: VWWall on 10 Aug 2010 15:09 markp wrote: > "VWWall" <vwall(a)large.invalid> wrote in message >> A couple of people have tried modeling the bulb in series with an >> inductance. The current does rise above the expected, but not enough to >> fail the bulb. >> >> Paul Hovnanian was on the right track. It's possible to conceive a two >> terminal device which could behave in this manner, but it would involve >> the storage of energy and the release of that energy in a way that would >> over-voltage the bulb. Any ways I could conceive involved some sort of >> switch, operated at a precise time. >> >> A hint: The motor which consistently failed the bulb was a small >> capacitor start device. My theory may be wrong. > > Do you know of the exact motor construction that was used? There may be a > power factor issue here too, espcially if it was a switched capacitor type > where the power factor could change rapidly. > > Jim has kindly posted a lamp model, what we really need is a motor model > with the same construction as the fan. Anyone got one? > In a capacitor start motor there is a winding, connected in series with a capacitor, used to produce the rotating field required to start the motor. This circuit is then opened by a centrifugal switch when the motor speed exceeds a set value. Obviously the timing is critical here, as is the time-constant and resistance of the bulb in series with the motor. Too small a bulb "wattage" will result in the bulb burning at near normal current and the motor not even starting; a too large bulb will allow the motor to start normally and run at near normal speed. It would be interesting to instrument such a set-up. With a normal "fan motor", which uses a shaded pole configuration, the bulb acts as a resistance, its value depending on the final current, and acts to slow the motor. One would not expect any conditions which could cause bulb failure. Deriving a "Spice" model would be tricky, but perhaps doable. Unfortunately we don't have any more details of the original posters experiment. He lost interest after failing several bulbs. It's interesting that a fairly common device can result in a seemly impossible result. -- Virg Wall
From: Don Klipstein on 10 Aug 2010 18:11 On 6/08/2010 4:03 AM, VWWall wrote in part: >>>> I haven't tried the experiment myself, since I don't have a suitable >>>> small motor available, and with 120V incandescent bulbs on the >>>> endangered species list, I don't care to sacrifice even one! The upcoming USA incandescent lamp ban scheduled to take effect in phases from 2012 to 2014 has a lot of exemptions. Exempted ones include tubular, flame shape, globe shape, rough service, reflector flood and spot, in general ones 25 watts or less, and ones producing more than 2600 lumens (nearly all incandescent lamps 200 watts or more and some 150 watt ones), and ones with a base other than "right hand" threaded E26 or E27 medium screw. I list these and other exemptions in: http://members.misty.com/don/incban.html -- - Don Klipstein (don(a)misty.com)
From: Paul E. Schoen on 10 Aug 2010 20:10
"Don Klipstein" <don(a)manx.misty.com> wrote in message news:slrni63jlf.b88.don(a)manx.misty.com... > On 6/08/2010 4:03 AM, VWWall wrote in part: > >>>>> I haven't tried the experiment myself, since I don't have a suitable >>>>> small motor available, and with 120V incandescent bulbs on the >>>>> endangered species list, I don't care to sacrifice even one! > > The upcoming USA incandescent lamp ban scheduled to take effect in > phases from 2012 to 2014 has a lot of exemptions. > > Exempted ones include tubular, flame shape, globe shape, rough service, > reflector flood and spot, in general ones 25 watts or less, and ones > producing more than 2600 lumens (nearly all incandescent lamps 200 watts > or more and some 150 watt ones), and ones with a base other than "right > hand" threaded E26 or E27 medium screw. > > I list these and other exemptions in: > > http://members.misty.com/don/incban.html That is very interesting (and a little disturbing). I did not realize that an outright ban on incandescent lamps was set to be implemented here in the US. Even though I am a greenie and a Sierra Club member since 1975, I really disagree with outright bans on products that may not be as efficient as other technologies. The proper way to control production and sale of something that is determined to be detrimental to the environment, health, or other item of concern to society, is to tax it appropriately and in accordance to how much damage it may cause and the cost of remedying that damage. Incandescent lamps are not always inferior to more efficient replacements. In winter, especially if a home uses electric heat, an incandescent lamp is nearly 100% efficient if you factor in the heat as a valuable output. If you are seated next to a warm incandescent lamp you might even turn down the thermostat and allow the rest of the room to be colder, resulting in a net saving. And many CFLs do not work well in extreme cold, although they are OK down to most minimum temperatures here in MD. Also, CFLs are more hazardous if they break or are put in landfills rather than properly recycled. But LED lamps will probably soon replace most CFLs. There are also ways to get around a ban of this type with so many exceptions. What about stringing 10 automotive 12 VDC lamps in series and mounting them on a standard Edison base? BTW, how long do you think a CFL will remain lit after it has broken? My dog pulled a desk lamp with a CFL onto the floor and I saw that it remained lit, but a large part of the lamp had broken. By the time I pulled the plug it had probably remained lit for as long as 10 seconds. When I saw that the bulb had broken and only two short tubes of glass remained, I tried plugging it back in about 10 seconds later. It actually lit again, for a couple of seconds, before going out for good. Paul |