Author Topic: Resistance of classic Mogul Incandescent bulbs  (Read 677 times)
lights*plus
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Resistance of classic Mogul Incandescent bulbs « on: August 09, 2016, 01:59:10 PM » Author: lights*plus
I'm measuring 25 Ohms for typical 40-60 watt lamps and 13 Ohms for 100w medium bulbs, while my 300W mogul bulb is 9 ohms.

What was the typical Ohms values for the large 500 & 750 watt street-light bulbs of the past..? and are they different now? I've read that they were 1 ohms.
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Re: Resistance of classic Mogul Incandescent bulbs « Reply #1 on: August 09, 2016, 02:11:17 PM » Author: wattMaster
At what voltage?
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Re: Resistance of classic Mogul Incandescent bulbs « Reply #2 on: August 09, 2016, 06:08:51 PM » Author: lights*plus
Not powered, with an ohmeter only, unlit. I suppose heating will ultimately make the bulb highly resistive.
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Re: Resistance of classic Mogul Incandescent bulbs « Reply #3 on: August 09, 2016, 06:58:03 PM » Author: wattMaster
Not being on doesn't matter, what's the voltage? Voltage determines Ohms.
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Re: Resistance of classic Mogul Incandescent bulbs « Reply #4 on: August 09, 2016, 11:18:12 PM » Author: Medved
All lamps are operating at about the same temperature and all ale tungsten.
So the hot to cold resistance ratio "has no other choice" than being all the time exactly the same.
So if 100W is 13 Ohm, 500W would be 5x less so 2.6 Ohm, the 750W would be then about 1.7 Ohm. Of course, assume all the same voltage rating.
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Re: Resistance of classic Mogul Incandescent bulbs « Reply #5 on: August 09, 2016, 11:55:21 PM » Author: lights*plus
Medved to the rescue again. This is what I was looking for but didn't know exactly how to ask. 1000w would be near 1.3 Ohms. But I was wondering did the bulbs of 80-90 years ago have different resistance than present tungsten bulbs? I'd think they were the same since tungsten is the same as today's tungsten. So the Ohms I came across must have been for carbon or osmium lamps, differenet meterial?
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Re: Resistance of classic Mogul Incandescent bulbs « Reply #6 on: August 10, 2016, 01:53:18 AM » Author: Ash
Maybe not, if they were running the filament at lower temperature back then
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Re: Resistance of classic Mogul Incandescent bulbs « Reply #7 on: August 10, 2016, 04:09:54 AM » Author: Medved
Medved to the rescue again. This is what I was looking for but didn't know exactly how to ask. 1000w would be near 1.3 Ohms. But I was wondering did the bulbs of 80-90 years ago have different resistance than present tungsten bulbs? I'd think they were the same since tungsten is the same as today's tungsten. So the Ohms I came across must have been for carbon or osmium lamps, differenet meterial?

If they were tungsten and operated at the same temperature (at that time the chemistry and operating conditions had quite settled down), the ratios should be the same.
But the older lamps may have been designed for lower temperatures (to compensate the life for the inferior metal processing), then the ratio would be lower.

Osmium or platinum metals or alloys will of course have different thermal properties, so the resistance will be different.

And the carbon is completely opposite: Cold lamps have way higher resistance than when hot, because carbon has a negative temperature coefficient...
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Re: Resistance of classic Mogul Incandescent bulbs « Reply #8 on: August 12, 2016, 07:53:42 AM » Author: wattMaster
Medved to the rescue again. This is what I was looking for but didn't know exactly how to ask. 1000w would be near 1.3 Ohms. But I was wondering did the bulbs of 80-90 years ago have different resistance than present tungsten bulbs? I'd think they were the same since tungsten is the same as today's tungsten. So the Ohms I came across must have been for carbon or osmium lamps, differenet meterial?

If they were tungsten and operated at the same temperature (at that time the chemistry and operating conditions had quite settled down), the ratios should be the same.
But the older lamps may have been designed for lower temperatures (to compensate the life for the inferior metal processing), then the ratio would be lower.

Osmium or platinum metals or alloys will of course have different thermal properties, so the resistance will be different.

And the carbon is completely opposite: Cold lamps have way higher resistance than when hot, because carbon has a negative temperature coefficient...
And were there carbon lamp ballasts?
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Re: Resistance of classic Mogul Incandescent bulbs « Reply #9 on: August 12, 2016, 08:31:35 AM » Author: Medved
And were there carbon lamp ballasts?

What do you mean?
Carbon lamps alone didn't need any ballast at all, they run directly of mains.
Carbon lamp used to ballast something? What should be that "something"?

Carbon arc lamps used either resistance as a ballast, or were just connected (many lamps in series) to a generator acting more like a current source.
Cooper-Hewitt lamp used resistor as ballast.
Both above were of too high wattage ratings, too high for carbon filament lamps. After all the filament incadescent lamps was developed mainly to have something suitable for low output applications like home lighting or so, for the high power use the arc lamps and later the Cooper-Hewitt tubes were way more efficient, so were dominating the market.

The modern discharges came only way later, when the tungsten filament incandescent was already the standard light source. In fact they all needed the tungsten metallurgy for the discharge tubes alone, so at that time was way practical to use tungsten filament when the integrated ballast was needed. And for standard use, the AC electricity was already a common place and the (principally) loss-less inductive reactors were rather known technology, so the standard HID installations used these as ballasts...
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Re: Resistance of classic Mogul Incandescent bulbs « Reply #10 on: August 12, 2016, 08:39:31 AM » Author: wattMaster
And were there carbon lamp ballasts?

What do you mean?
Carbon lamps alone didn't need any ballast at all, they run directly of mains.
Carbon lamp used to ballast something? What should be that "something"?

Carbon arc lamps used either resistance as a ballast, or were just connected (many lamps in series) to a generator acting more like a current source.
Cooper-Hewitt lamp used resistor as ballast.
Both above were of too high wattage ratings, too high for carbon filament lamps. After all the filament incadescent lamps was developed mainly to have something suitable for low output applications like home lighting or so, for the high power use the arc lamps and later the Cooper-Hewitt tubes were way more efficient, so were dominating the market.

The modern discharges came only way later, when the tungsten filament incandescent was already the standard light source. In fact they all needed the tungsten metallurgy for the discharge tubes alone, so at that time was way practical to use tungsten filament when the integrated ballast was needed. And for standard use, the AC electricity was already a common place and the (principally) loss-less inductive reactors were rather known technology, so the standard HID installations used these as ballasts...

I'm asking if there were ballasts for carbon lamps because the negative temperature coefficient would lead to thermal runaway.
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Re: Resistance of classic Mogul Incandescent bulbs « Reply #11 on: August 12, 2016, 09:27:54 AM » Author: Ash
I think it is not badly enough negative to cause a runaway

Evaluating this can be done graphically :

 - If you know the resistance as function of the temperature, then you can also express the current as function of the temperature

 - If you know the temperature as function of the power, then you can also express the temperature as function of the current

 - Now plot them both on one temperature/current chart, and see whether they would tend to "drag" each other in the direction of a runaway. For low temeratures it likely will, but maybe it reaches some acceptable stable point at higher temperature, in which case it will only run away (or we can call it warm up) untill reaching this point and stop there
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Re: Resistance of classic Mogul Incandescent bulbs « Reply #12 on: August 12, 2016, 12:12:39 PM » Author: Medved
The thing is, the filament dissipates all power by just radiation. And the radiated power is proportional to T^4. That is very steep, way steeper than the temperature vs power (close to linear). So even when the stable point is not as stable as with the metal filaments, it is good enough to keep it stable. By the way the steep power vs temperature curve is, what makes even the incandescent lamps rather linear devices around the rated operating point. Contrary to the ~5%  power level, where the metal incandescents tend to behave way closer to a constant current regulators (the dominant gas cooling of the barretters is there just to make the power vs temperature way more linear, so the temperature may change way steeper with the power).

But the negative resistance characteristics, together with the not well controlled manufacturing process at their time was the prime cause, why the performance of the carbon filament lamps varied so much. On the other hand the negative resistance makes the lamp to start softly, without any part of the filament overheating (like the case with tungsten lamps, leading to most failures happening at lamp start)
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Re: Resistance of classic Mogul Incandescent bulbs « Reply #13 on: August 12, 2016, 12:20:56 PM » Author: Ash
So it is possible that with advanced manufacturing the Carbon Incandescents may surpass Tungsten in some properties ?
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Re: Resistance of classic Mogul Incandescent bulbs « Reply #14 on: August 12, 2016, 07:58:12 PM » Author: wattMaster
So it is possible that with advanced manufacturing the Carbon Incandescents may surpass Tungsten in some properties ?
Would there be a possibility that Carbon filaments could be more efficient than Tungsten?
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