# A very basic inductance resistance circuit ( a lamp )

Hi all
A brief intro
I build motorcycles
and have many a year of cad underneath me belt. I know me watts from me ohms and years ago there was a software that I used to design my wiring for the bike I was building but it was windows and no longer exists.
I am a linux user ( the doctor said I should recover )
So I looked for software, where I could design simple circuits for my bikes
it led me here
So, all I have to do is “simulate” a simple circuit, batt 12v, switch incandescent lamp and ground
I simulated a simple resistor circuit without problems
However, the spice model of a lamp shows to be modeled as an inductor, and as it is a DC circuit, if I’ve got this right at max current-voltage ( 5t ) inductance is not an issue
So, how would I model a 55w incandescent bulb circuit?
as a simple resistor ? created a new component?
Also, can I add “layers” to my schematic?

Stephen

I don’t really see that an inductor would be relevant for a bulb.
It’s basically a non-linear resistor (like a PTC) and should be modelled as such for DC analysis.
I’m on V7 and don’t know of any layers in schematic. Can’t say about V8.
Partitioning a schematic is done using hierachical sheets.

Are you sure you need to simulate it?
I think that it is much more work to get enough accurate models to be able to get valuable results from simulation than simply build and do some measurements.
If you are interested in stable state at the end than knowing the bulb voltage and power you can calculate its R (in hot state) and you simply can calculate everything.
But if you want to see how currents look when it is switched on and then got hot I expect problems to get model than will accurately model for example the self hitting time constant.

Hi there
Yes, I would like to model it
As I can play around with wire sizes , bulb sizes and check things
I can just roll out a coil of wire and have done just that, but Its quicker and easier to draw , AND i dont have to go through all calculations for each change Once the drawing is set up !

Stephen

I know right but when I select “spice” lamp, its default is inductance hence my question
I would just model it as a resistance
But I’m no expert far from the maddening crowd am I

I just checked, and in V7 the “Device” library “Lamp” symbol indeed shows an inductance. Dunno why.
You’ll need to find a bulb model somewhere anyway, none of the built-in models will bring you anything.

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Maybe they try to show the filament of a light bulb and it looks like an inductance?

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No. Under the simulation tab in “Symbol Properties” it’s actually listed as an inductor. And the “Lamp” symbol is just a cross within a circle. No filaments shown.

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A heated incandescent lamp in steady state is a resistor. If you have 12 V and 55 W, you know what the resistance might be.

That the “Symbol Properties” tell us it is an inductor is simply wrong (maybe due to some automatism: Lamp, in short LA, oh starts with L, must be an inductor). Of course the filament (the “coil”) has some inductance, more than a straight wire, but we do not run the lamp at 100 MHz, but with DC, so L does not matter.

It becomes interesting when I want to simulate the transient response of switching a lamp on. As Piotr has said, the cold resistance of the lamp wire is much less than its hot resistance. So you will have a current bump during switching on, until the filament is hot (that’s why these lamps say good-bye typically during switching on). Modelling the details is of course possible but very tedious (see for example https://groups.google.com/g/sci.electronics.cad/c/I9QfewHAaSI, or Incandescent Lamp - CircuitLab, not tested myself!)…