Nernst lamps

[SPBrewer]

The thing I don't like about barreter's are they look too much like light bulbs.  Same with light bulbs. 
Why have a 100 watt light bulb to power another light?  Might as well just use the 100 watt light bulb.
I'll bet somebody out there has a whole @*#&(! load of .002 Iron wire that they can't get rid of.
Who would have guessed that yttria-stabilized zirconia would be easier to obtain than some iron wire? 

[Tower]

Why have a 100 watt light bulb to power another light?  Might as well just use the 100 watt light bulb.

Thats my problem, its hard for me to justify such a creation to myself even though it is the easiest and cheapest solution.

[elShoggotho]

MOSFET current limiter. Might build one myself.

[Siliconous Skumins]

MOSFET current limiter. Might build one myself.

Uhm.... didn't I already mention one of them a few pages back?...

SS

[SPBrewer]

MOSFET current limiter. Might build one myself.

Uhm.... didn't I already mention one of them a few pages back?...

SS

Somehow a MOSFET just doesn't have a good Steampunk feel to it.
I'm going to look for the iron wire some more.  Should I give up, I "may" use the light bulb approach.

Stop your chatter and say something Latin-ish.   Geena Davis as Morgan in "Cut Throat Island" (1995)

[Siliconous Skumins]

MOSFET current limiter. Might build one myself.

Uhm.... didn't I already mention one of them a few pages back?...

SS

Somehow a MOSFET just doesn't have a good Steampunk feel to it.
I'm going to look for the iron wire some more.  Should I give up, I "may" use the light bulb approach.

Stop your chatter and say something Latin-ish.   Geena Davis as Morgan in "Cut Throat Island" (1995)

True, not much of a steampunk feel to it, but then it can be hidden easily enough - not unlike a lot of modern tech in we see in steampunk gadgets on this very forum everyday...    I get you point though, I feel the same way.


You might have better luck in finding something via one of the antique radio collector forums, early valve radios often used the iron-hydrogen resistor / barreters / ballasts.  I think you would be looking around the 1930's or earlier, as AC valves were more commonplace by then, and and electricity supplies were more standardized, so they were not needed so much. Though there were some resistors of this sort still in use up to the mid 60's (or at least still available as spare parts) in radios and some televisions.
There were two types in use though, the glass envelope iron-hydrogen resistor, and the metal grill / cage type which is actually just a massive power resistor (wire (prob nichrome..?) wound around a mica former). The first is used for regulation, the last is just a dropping resistor.

Actually strictly speaking there were also two types of iron-hydrogen resistor. The first was just iron wire in hydrogen which has a positive temperature coefficient. The second type also had a negative temperature coefficient resistor within the same housing to act as an inrush current limiter. For the Nernst lamp, I'm not sure which would be the better choice. The PTC / NTC type may help prolong the filament life by avoiding sudden thermal shocks...


Quid me vis dicere in latina? Fortasse "aut viam inveniam aut faciam" datum sit opportuna loco profertur?


SS

[DrArclight]

I still say a variable core inductor would be a more steam-punk current control mechanism.

[J. Wilhelm]

Correct me if I'm wrong, or if too many years have passed since I tool some electric engineering courses as electives, but the real part of the complex impedance of an inductor is just proportional to the frequency (for AC applications) at 60 Hz that is just a number-whatever that may be.  The glower will still get hotter and hotter and just demand more current from the inductor ad infinitum until the effective resistance of the glower is zero and the current is determined by what essentially is an energy dissipator. (just seems to me dissipation is unavoidable thus killing your efficiency- be it by radio waves or infrared EM).

If the problem is the variable resistance as a function of temperature of the glower, can we make a variable inductor with a temperature dependent mechanism, and can we benefit from it?  A negative positive temperature coefficient inductor? As the temperature goes up the variable core inductor changes, with something like a bi-metallic thermometer adjusting the impedance?  Would that lead to oscillations?  Or have I just stupidly repeated some idea already expressed by someone else (my apologies in that case, I'm too lazy to read all posts and right now a bit drunk as well  ) ?

[elShoggotho]

The Nernst lamp needs a positive temperature coefficient, since the glower already has a negative coefficient. You need to limit the current, because otherwise the glower just burns up.

[J. Wilhelm]

The Nernst lamp needs a positive temperature coefficient, since the glower already has a negative coefficient. You need to limit the current, because otherwise the glower just burns up.

Corrected    I am a little drunk    Yes, limiting the current, that is understood (it's like a current limiting resistor for an LED), but my concern is how much the resistor/ barreter / inductor/ lightgbulb is emitting in EM (including IR and/or radio), thus leading to waste and if we can do something about that.  A plain inductor (electrical ideal) is independent of temperature, but maybe we can preserve some of the glower impedance by not letting the glower be reduced to take such a small part of the electrical load (like the example where a light bulb is used as a barreter, and there is so much dissipation that both the light bulb and the Nernst glower shine!  I'm also of the opinion that barreters, although "ideal" are just in essence a type of ambient pressure inert-gas "light bulb" looking device!  I share Mr. Brewer's opinion; I guess we can see the obvious advantage of the light bulb in terms of simplicity and efficiency.    Most vexing problem, that current limiter.

[Mr. Consciousflesh]

The iron-hydrogen resistor has one big advantage over light bulbs - it doesn't glow.  Unfortunately my project of building one has encountered some serious problems. I found a company which sells pure iron wire but I cannot afford their prices now . Also it seems that I cannot make glass envelope big enough for it without a proper glass lathe and the annealing furnace .
There are two more possibilities of building a steampunk-worthy current limiter . Both of them are electromagnetic and both of them use negative feedback . The first one uses a stack of graphite disks compressed with a spring and connected in series with a glower and small electromagnet which counteracts the spring . The resistance of the graphite stack lowers with increasing pressure , so this circuit should regulate the current the same way as my MOSFET constant current source does.
The second solution is even simpler  but requires more calculations to build it correctly . It is basically a vertical coil with a sliding iron core suspended on a spring . The inductance (and thus reactance) of the coil depends on how much of the core reside inside the coil . The tricky part is to find a point at which the spring compensates the pulling force of the electromagnet.  It may be also necessary to add a fluid damper to minimise the vibration created by this device.

[J. Wilhelm]

The latter is more along the lines of what I was thinking, but the graphite stack is rather elegant!

[mightybuddha]

Chaps, have you considered a mechanical pulse circuit instead of a resistor?

It would be quite easy to rig up a rotary "spark gap" (though probably more of a rotary relay since mains voltage would be too low for a spark gap). 

[Tower]

I've actually thought of using a pulsed current controlled by a heavy duty relay. By just manually flipping a switch rapidly I was able to keep the lamp going without blowing up.

The only problem is that Imagine it would wear out pretty quickly.

[elShoggotho]

Rotary brush contact switch. Run it with a toy steam engine.

[mightybuddha]

Rotary brush contact switch. Run it with a toy steam engine.

exactly

That will give you a more efficient means of controlling the current, though it can also be used for self regulating the current by using an electric motor running the switch in series with the lamp.  As the lamp draws more power, the motor accelerates and so allows less current through the circuit due to back emf, and also as the motor speeds up, the frequency of the switch would speed up and since the motor is essentially an inductor it will have a higher impedance at higher frequencies.

[Siliconous Skumins]

It will work, but I can see that causing bad RF interference and some 'interesting' effects on the power line.  

It would need some shielding and filtering, but it could be done. Thing is I see this as being overly complicated and adding multiple points of failure.

Personally I think a reactive ballast like those used for fluorescent lamps would be an easier device to use. Maybe not the most efficient, but probably better than the Iron-Hydrogen barretter. Shouldn't be too hard to wind up an inductor and pair it with a capacitor.

Then again a single capacitor in series could be used as a ballast! The lamp that Mr. Consciousflesh made, for example, requires 118V, 0.3A @ 50Hz line frequency, and would require an Xc of :
(230 - 118) =373Ω
(Xc) = 1 / ( 2 * Pi * F * C )>   = 8.533784μF

So that would be an 8.5μF 400V capacitor. Now that is cheap and easy enough to find...  

SS

[mightybuddha]

It will work, but I can see that causing bad RF interference and some 'interesting' effects on the power line.  

It would need some shielding and filtering, but it could be done. Thing is I see this as being overly complicated and adding multiple points of failure.

Personally I think a reactive ballast like those used for fluorescent lamps would be an easier device to use. Maybe not the most efficient, but probably better than the Iron-Hydrogen barretter. Shouldn't be too hard to wind up an inductor and pair it with a capacitor.

Then again a single capacitor in series could be used as a ballast! The lamp that Mr. Consciousflesh made, for example, requires 118V, 0.3A @ 50Hz line frequency, and would require an Xc of :
(230 - 118) =373Ω
(Xc) = 1 / ( 2 * Pi * F * C )>   = 8.533784μF

So that would be an 8.5μF 400V capacitor. Now that is cheap and easy enough to find...  

SS

That sounds like a much better idea! Good thinking!

[Mr. Consciousflesh]

Personally I think a reactive ballast like those used for fluorescent lamps would be an easier device to use. Maybe not the most efficient, but probably better than the Iron-Hydrogen barretter. Shouldn't be too hard to wind up an inductor and pair it with a capacitor.

I'm not so sure. The fluorescent lamps are not as nonlinear load as Nernst's glowers . The reactance of the ballast inductor is almost independent from the current , and would not compensate the negative characteristics of the ceramics . There has to be something to control the reactance , for example a sliding core or a magnetically saturated core. I think I will try to build the graphite stack regulator because I believe it will be the best looking solution to our problem

[SPBrewer]

I may have dreamed it, but didn't someone recently say they had found a source for the Iron Wire, but that it was rather expensive?  I can't seem to find the post.
IF someone can locate .002 inch iron wire, I would be glad to purchase enough for both of us.

[Tower]

Like I said, I don't know much about electronics but could you do anything with a 2000MFD 450V capacitor? I have a box full that I don't know what do with.

[J. Wilhelm]

Personally I think a reactive ballast like those used for fluorescent lamps would be an easier device to use. Maybe not the most efficient, but probably better than the Iron-Hydrogen barretter. Shouldn't be too hard to wind up an inductor and pair it with a capacitor.

I'm not so sure. The fluorescent lamps are not as nonlinear load as Nernst's glowers . The reactance of the ballast inductor is almost independent from the current , and would not compensate the negative characteristics of the ceramics . There has to be something to control the reactance , for example a sliding core or a magnetically saturated core. I think I will try to build the graphite stack regulator because I believe it will be the best looking solution to our problem

I like the graphite stack current limiter, but...

The Nernst lamp shown in the wiki site had a ballast, did it not?
If I forget about the jabber I talked about regarding efficiency, at the end of the day you need a temperature independent resistance (or at least one that asymptotically reaches a value at the operating temperature) in the circuit besides the pure reactance of the capacitor and/or inductor you could fetch, because, as it's pointed out, the overall temperature coefficient is negative for the ceramic. In this context, I'm equating temperature and the current across the ceramic glower.

My "anything goes" instinct is to assume the glower will have a negligible or very low resistance (hence needing an external load like a barreter), unless I can control the temperature of the glower! That turns now into a heat transfer problem (rather than looking at an active current limiter).

I have this image in my mind of a stack of ceramic elements sandwiched between resistors (yeah i know, what about the 1500 C? Another ceramic?) acting as heat sinks of sorts... Obviously the ballast was enough, but somehow the glower reached an operating temperature asymptotically in commercial Nernst lamps.

[Rooster]

I've only skimmed the thread so far so forgive me if this isn't quite what you are looking for.

I was just reading the diyAudio newsletter and though these might be of interest:
http://www.diyaudio.com/forums/diyaudio-com-articles/200460-l-amp-simple-sit-amp-part-1-a.html
http://www.diyaudio.com/forums/diyaudio-com-articles/202480-l-amp-simple-sit-amp-part-deux.html

The first article is an amplifier build that uses two 300 Watt incandescent light bulbs as resistors, these are replaced by a large spool of copper magnet wire in the second article.

[Hektor Plasm]

Hmm. Although I can't lay my hands on any right now,I seem to recall the green coated 'gardening wire' used to tie plants to canes etc is made of soft iron wire. I'm not sure of the diameter,but it may be possible to reduce the diameter somewhat by stretching a length.

HP

[SPBrewer]

Hmm. Although I can't lay my hands on any right now,I seem to recall the green coated 'gardening wire' used to tie plants to canes etc is made of soft iron wire. I'm not sure of the diameter,but it may be possible to reduce the diameter somewhat by stretching a length.

HP

What's a good test to tell the difference between Steel and Iron?  If they are Iron, I think I could stretch it using a little heat.