Household Type 240/120 Volt Power (240 Volt Center Tapped transformer)

[iceworm]

(posted in sureal time ccc)
On a 100 W 120 V bulb I read about 9.4 ohms with a Fluke 27. This applies about 0.004 V at this resistance level.

With 1.56 V applied the current is 0.0813 A and a calculated resistance of 19.2 ohms.

What voltage is applied for your 19 ohms cold measurement?

I'm not sure what part of this you missed:

iceworm][/B]
Tungsten lamps have a positive temperature coeficient. As the fillament gets hotter, the resistance goes up. Here is an example: These are nominal numbers

This has nothing to do with the OPs discussion. However, if you must know, I used a pecision 5000V source, current was 263.158A, pulse duration .001us. Energy delivered .001315J.

OP: This has nothing to do with your questions. I'm trying to get out as gracefully as I can for helping with the bunny trail. Tungsten temperature coeficient has nothing to do with the topic. I'm just jerking gar's chain.

ice

 

[gar]

141208-1954 EST

iceworm:

I am really curious what instrument you used, or was it measured with V and I?

Since my 1.5 V measurement comes close to your measured value. I suspect that your measurement had something more in the range of 1 to 2 V across the filament.

My guess is that Fluke is using an active constant current source for their measurement as this would provide a linear voltage proportional to resistance. With the extremely low voltage from Fluke with a 10 ohm resistance there is not enough power to noticeably change the resistance within the accuracy of the meter.

Using a General Radio Decade Resistance box I can generally verify that Fluke is using an active constant current source.

.

 

[iceworm]

141208-1954 EST

iceworm:

I am really curious what instrument you used, or was it measured with V and I?

Since my 1.5 V measurement comes close to your measured value. I suspect that your measurement had something more in the range of 1 to 2 V across the filament. ....

I sincerely appoligize for my poorly expressed remarks. I could have done better. Be that as it may, here is the method I used:
I picked 100W which gives 140hms at 120V. I picked the high temperature of 1400C cause that is about right for a normal incandescant. I used .0045 C^-1 for W temp coeficient and 20C for room temp. This calculates to 19 ohms at 20C. Truely - it was just an example.

However, I would like to leave this post for the OPs discussion. We aren't helping talking about tungsten temp coeficients.

ice

 

[kwired]

So a constant speed motor is not, in fact a constant speed motor either. All these years we have been lied to. For all practical purposes and surely for the purposes of the OP's question, an incandescent light bulb is a constant resistance. Why confuse the issue?

One must realize they are constant resistance once up to operating temperature, but are not same resistance hot vs cold. Change the input voltage and you probably don't get same operating temp and therefore a different resistance than at full voltage and would need to factor that into any calculating as well.

 

[ptonsparky]

My intent was to make him aware of more than just a measured resistance can come into play. I was given the same problem 40 some years with no one to even give a hint as to why things didn't add up.


I have a fair grasp on my intelligence and even a better sense of my lacking education. I expected someone to fill in the blanks and as usual, they did and they were.

Excuse me for the distraction.

 

[GoldDigger]

There are two points of difference in load behavior to be marked. An incandescent bulb is resistive but non linear in that the resistance varies with voltage. But current will never increase as voltage is reduced slowly.
A constant power load such as a motor, OTOH, can increase current draw as voltage is reduced.
Neither has the type of non linearity associated with a distortion power factor.