Burn out 120V lamp on 120V circuit?
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From: Paul Hovnanian P.E. on 5 Aug 2010 22:10 VWWall wrote: > > Jim Thompson wrote: > > On Thu, 05 Aug 2010 11:03:28 -0700, VWWall <vwall(a)large.invalid> > > wrote: > > > <snip> > >> 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. > >> > <snip> > >> 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? > > > > Having burned myself seriously as a kid, using an Erector Set motor > > winding to blow flashbulbs (?), I can assure you that a bouncing > > contact will do it ;-) > > > > (?) The flashbulb (Press 25) melted over my finger :-( > > > > ...Jim Thompson > > Not quite the same thing. I have had #25 flash bulbs go off in my > pocket from EMF radiated by trolley lines. An ordinary incandescent > bulb requires much more energy to cause its filament to burn out. Flash bulbs aside, motors store significant energy in their magnetic fields. Motors are far from "two terminal passive devices". It may take some sort of switching event (commutation for example) to get an inductive kick to blow a lightbulb, it may be possible. -- Paul Hovnanian mailto:Paul(a)Hovnanian.com ------------------------------------------------------------------ On a clear disk, you can seek forever.
From: Greegor on 5 Aug 2010 23:47 Ok, So you're thinking that the motor is creating some sort of inductive kick or something a bit like a slower version of inductive kick caused by the motor's flyweel effect and switching from a spinning motor to a spinning generator? What kind of voltage do you suppose the spinning generator effect could add to the circuit? Can't a 100W 120 Volt Incandescent light bulb take a momentary surge of double or triple the normal voltage?
From: Jim Thompson on 5 Aug 2010 23:54 On Thu, 5 Aug 2010 20:47:31 -0700 (PDT), Greegor <greegor47(a)gmail.com> wrote: >Ok, So you're thinking that the motor is creating >some sort of inductive kick or something a bit like >a slower version of inductive kick caused by the >motor's flyweel effect and switching from a spinning >motor to a spinning generator? > >What kind of voltage do you suppose the >spinning generator effect could add to the circuit? > >Can't a 100W 120 Volt Incandescent light >bulb take a momentary surge of double or >triple the normal voltage? Not if the filament is cold. ...Jim Thompson -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | Spice is like a sports car... Performance only as good as the person behind the wheel.
From: VWWall on 6 Aug 2010 01:05 Paul Hovnanian P.E. wrote: > VWWall wrote: >> Jim Thompson wrote: >>> On Thu, 05 Aug 2010 11:03:28 -0700, VWWall <vwall(a)large.invalid> >>> wrote: >>> >> <snip> >>>> 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. >>>> >> <snip> >>>> 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? >>> Having burned myself seriously as a kid, using an Erector Set motor >>> winding to blow flashbulbs (?), I can assure you that a bouncing >>> contact will do it ;-) >>> >>> (?) The flashbulb (Press 25) melted over my finger :-( >>> >>> ...Jim Thompson >> Not quite the same thing. I have had #25 flash bulbs go off in my >> pocket from EMF radiated by trolley lines. An ordinary incandescent >> bulb requires much more energy to cause its filament to burn out. > > Flash bulbs aside, motors store significant energy in their magnetic > fields. Motors are far from "two terminal passive devices". > It depends on how you define "passive device". In this case I defined it as a "two terminal black box" containing no energy source. It's easy to dream up a "box" that takes input energy, stores it and sends it back in a way that can overvoltage the bulb to failure. It is hard to see how a common AC induction motor can do this. > It may take some sort of switching event (commutation for example) to > get an inductive kick to blow a lightbulb, it may be possible. > You're on the right track! Those that tried a Spice simulation modeled the bulb's variable resistance well, but considered only the static inductance of the motor's windings. Virg Wall, P.E.
From: Greegor on 6 Aug 2010 01:29
> >Ok, So you're thinking that the motor is creating > >some sort of inductive kick or something a bit like > >a slower version of inductive kick caused by the > >motor's flyweel effect and switching from a spinning > >motor to a spinning generator? > > >What kind of voltage do you suppose the > >spinning generator effect could add to the circuit? > > >Can't a 100W 120 Volt Incandescent light > >bulb take a momentary surge of double or > >triple the normal voltage? JT > Not if the filament is cold. But but... (grin) By the time the motor gets spinning enough to generate the killer curent, isn't the filament warmed up? Naa.... How big of a plain old inductor would it take to cause this effect? |