UncleJoe1985
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neon sign transformer temperature and lifetime
Hi everyone. I'm using a neon sign transformer in a Birkeland Eyde reactor for HNO3 production, but am wondering how long can I expect it to last. The
transformer is a 9KV @30mA Franceformer and I notice the sides sometimes get very uncomfortably hot to touch (probably 70 C). Actually this depends on
how long I allow the arcs travel on my Jacobs ladder. If I blow upwards using a strong pump, the arcs only travel about 2" and the transformer gets
very hot. When I use a weaker pump, the arcs travel 10" and spreads out a lot more, which results in a lower temperature as expected.
What I'm really worried about is how long can I expect to use the NST for this purpose. I understand that NSTs are not designed for this purpose. I
suppose every time the arc breaks, the voltage spike causes damage. Does anyone have experience with how long they last?
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kclo4
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I'm sorry I can't help you with this, but I'm curious as to how well your Birkeland Eyde reactor going? How much nitric acid have you produced and how
much time it takes?
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UncleJoe1985
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I've rebuilt my reactor to address the deficiencies I addressed at the bottom of this thread. I've ran it for a few hours, but the tube connecting the main cell melted.
However, I've reason to be pleased. I've put a gallon reservoir in between and I see a moderately dark color when looking through it, which means I'm
generating a much larger concentration of NO2. I've also come up with an ingenious way for better absorbing the gas. I've created grooves inside a
round container and fit 6 polycarbonate DVD layers with holes drilled through them, to simulate a bubble cap tray. I haven't measured its
effectiveness yet, but my visual inspection seems that the gas residency time is a lot longer - there's a 3mm layer of gas between each layer of
liquid, which definitely should be an improvement.
Once I get more results, I'll create a web page and post my findings.
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Mr. Wizard
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The maximum amperage output is supposed to be .03 amp. ( Watts = 9000x .03= 270)When you operate it as an arc, the voltage drops and you are
essentially shorting out the secondary. The voltage is only needed to start the arc, not maintain it. Once the current flows through the air and
ionizes it, it only takes about 20 volts to maintain the arc. You are actually limiting your production by using such a small current. I don't think
you even actually get the full 270 watts. You should be trying for a higher current arc from a welder or other transformer and using a magnetic field
to flatten out the arc so the nitric oxides formed are quickly cooled. You might consider using the HV transformer through a current limiting
resistor to initiate the arc on the cycle peaks and then let transformer supply the heat to make the oxides. Remember,it's the heat that makes the
Nitric Oxides, not the voltage gradient, as in Ozone. You might even make a mini Tesla coil to keep the arc going and use inductors to block the high
frequency AC from the current supplying transformer.
A rule of thumb about how hot they are is: If you can't keep your hand pressed against it for three seconds, it's too hot. This is while it's turn
OFF. I know you know, but everyone else reading this may not.
Another thing you can use is MOTs, or Microwave Oven Transformers. They are high enough voltage to start an arc and yet can carry a high current. Be
careful with these, they can kill. They will deliver a MUCH higher current than a Neon Sign transformer. Another advantage is they are laying on the
sidewalk on trash pick up day.
That's my two cents worth.
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hinz
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Microwave Oven Transformers will overheat even worse than NST's. NST's are stray field transformers <a
href="http://en.wikipedia.org/wiki/Transformer" title=>Leakage transformers, in the middle</a>
, they have a magnetic bypass between primry and secondary coil. The result is, that the prim. coil don't induct all current into the sec. coil ==>
self inductance ==> decrease of current trough transformer.
Maybe you can screw the magnetic bypass deeper into the transformer, I dont know how your NST looks like.
MOT's dont have a magnetic bypass, so the current will increase till they burn.
But MOT's could be useful as a <a href="http://en.wikipedia.org/wiki/Choke_(electronics)" title=>choke</a>, just shortcircuit the sec.
coil und plug it serial to the NST ==> uses self inductanse of the MOT to decrease current.
[Edited on 14-10-2008 by hinz]
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Mr. Wizard
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Yes Hinz is right about the current draw of these beasts. They are not saturated and so can draw more current than they should. They can be rewound
though, You could also put some resistance load in series to limit the current. 500 watt quartz halide lamps come to mind. These could even be used
in the secondary HV side. They can be tamed though and will deliver more amps than the biggest neon sign transformer. In an arcs amps = heat and heat
= nitric oxides. You may have to put something in the circuit to limit the current. I'm just saying the MOTs are cheap available and will handle
more power than NSTs. Do a google for "MOT welder" and "Saturable Core Reactor" and you won't be spending $50 for NST on eBay anymore. I have no
connection with any of the links that will pop up.
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