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: JosephKK on 12 Aug 2010 22:30 On Mon, 09 Aug 2010 18:41:12 -0400, PeterD <peter2(a)hipson.net> wrote: >On Mon, 9 Aug 2010 18:18:19 -0400, "Paul E. Schoen" ><paul(a)pstech-inc.com> wrote: > >> >>"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 > >Damn it, now I'm going to have to run an experiment! <bg> Suggestions >to motor specifications? Since we are talking a fan motor, maybe I'll >use my shop fan, and a spare 60 watt bulb. Sure, start with motors and lamps of about the same rating in normal watts.
From: JosephKK on 12 Aug 2010 22:38 On Mon, 09 Aug 2010 18:12:40 -0700, VWWall <vwall(a)large.invalid> wrote: >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. > >> 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. What is the watt ratinggs of the motor and the lamp? Capacitor start motors by definition include some kind of switch that changes when the motor is up to some approximate fraction of full speed. There are way too many variations for the starting switch to guess the operating characteristics.
From: JosephKK on 12 Aug 2010 23:18
On Thu, 12 Aug 2010 12:27:01 -0700, Jim Thompson <To-Email-Use-The-Envelope-Icon(a)On-My-Web-Site.com> wrote: >On Thu, 12 Aug 2010 13:49:36 -0500, bud-- <remove.budnews(a)isp.com> >wrote: > >>Paul E. Schoen wrote: >>> >>> "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. >> >>Surprising. I have see it at least a couple times in the newspaper and >>at least a half dozen times in the newsgroups I follow. I suspect it has >>appeared here as an example of the >>socialist-government-takeover-of-America (except the socialist that >>signed the bill was Bush 2). The loon from Minnesota (Michelle Bachman) >>tried to make it a big issue (ignoring, of course, what the ban really did). >> >>> 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. >> >>If you look at Don's link (in addition to what he wrote above) the ban >>does not cover a whole lot of incandescents. And the 'banned' lamps are >>not banned if they meet efficiency standards. There may be some current >>incandescents that do. >> >>> 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 > >I understand that you can apply 110VAC to the shriveled useless >testicles of a tree hugger and get a substantial amount of light (and >noise) for as much as TWO MINUTES... then you get smoke ;-) > > ...Jim Thompson You forgot to make the PC gender neutral chnages. |