Burn out 120V lamp on 120V circuit?
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From: Rich Grise on 6 Aug 2010 18:47 On Thu, 05 Aug 2010 11:03:28 -0700, 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. > ... > 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? It sounds impossible, but motors are inductive things, and there lie dragons and other things that go bump in the night. I once blew a 1/4A fuse that was in series with the primary of a Mouser 12.6V, 300 mA or so transformer; I was torture-testing the RS slide switch at the time, and presumably I switched it right at the peak of the inductive kick and the line voltage or some such. But _every time_ he turns it on? When he does just the motor without the bulb, does it run? What's it fused at? What's the rated current of the motor? What's the rating of the bulb? Thanks, Rich
From: AZ Nomad on 6 Aug 2010 20:29 On Fri, 6 Aug 2010 18:56:40 -0400, Paul E. Schoen <paul(a)pstech-inc.com> wrote: >"Joerg" <invalid(a)invalid.invalid> wrote in message >news:8c2la2F7vhU2(a)mid.individual.net... >> >> >> As in "charge us with more taxes"? It sure seems like that. That process >> has already been started. As expected :-( >It was largely Bush's tax cuts (and his wars) that led to the huge deficit. >The tax cuts are set to expire soon and if they are allowed to do so it will >mean a reversal of the present trend and an additional tax burden mostly on >the most wealthy. Not really an additional burden but elimination of a >previously established burden that was removed for political reasons. Pleaes don't feed the trolls.
From: Paul E. Schoen on 6 Aug 2010 21:51 "Rich Grise" <richgrise(a)example.net> wrote in message news:pan.2010.08.06.22.47.48.651697(a)example.net... > On Thu, 05 Aug 2010 11:03:28 -0700, 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. >> ... >> 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? > > It sounds impossible, but motors are inductive things, and there lie > dragons and other things that go bump in the night. > > I once blew a 1/4A fuse that was in series with the primary of a Mouser > 12.6V, 300 mA or so transformer; I was torture-testing the RS slide switch > at the time, and presumably I switched it right at the peak of the > inductive kick and the line voltage or some such. Transformers (and other inductive devices) may exhibit high inrush current which can be as much as the applied voltage / resistance. This is especially true if you happen to connect it at a phase angle that corresponds to the last current that flowed, where remanent magnetism has the greatest effect. A 4 VA transformer may only draw 30 mA normally, but the primary winding resistance is probably 50 ohms or so, and could draw a surge of 3 to 4 amps long enough to blow a fast acting fuse. > But _every time_ he turns it on? > > When he does just the motor without the bulb, does it run? What's it > fused at? What's the rated current of the motor? What's the rating of > the bulb? A 120V 100W bulb will have an operating resistance of about 120 ohms, but a cold resistance of about 12 ohms. Thus it will normally draw a surge of about 10 amps until it reaches incandescence. A motor can act as a generator, and if it is a PSC type its capacitor may conceivably for a resonant circuit which might cause transients high enough to destroy the lamp. http://psc-ir.com/FinalPapers09/09-E-ELM-0164.pdf http://sci.tech-archive.net/Archive/sci.electronics.design/2005-07/msg01555.html Paul
From: Tim Williams on 7 Aug 2010 05:05 Possible if the motor is large (high reactive current) and a suitable capacitor is placed across the lamp (thus resonating at 60Hz). Tim -- Deep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms "VWWall" <vwall(a)large.invalid> wrote in message news:E46dnYn4Ov9bYcfRnZ2dnUVZ_sGdnZ2d(a)earthlink.com... >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? > > -- > Virg Wall, P.E.
From: Spehro Pefhany on 7 Aug 2010 07:50
On Sat, 7 Aug 2010 04:05:08 -0500, the renowned "Tim Williams" <tmoranwms(a)charter.net> wrote: >Possible if the motor is large (high reactive current) and a suitable >capacitor is placed across the lamp (thus resonating at 60Hz). > >Tim That's not a 2-terminal device though. And we should reject the pathological case of a motor with a massive flywheel that is "plugged". Best regards, Spehro Pefhany -- "it's the network..." "The Journey is the reward" speff(a)interlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com |