Re: fluorescent lamp operating voltage - US 4,613,841.pdf (0/2)

On 19 Feb 2006 20:17:21 GMT, phil-news-nospam@xxxxxxxx
wrote:

On Sun, 19 Feb 2006 09:34:55 -0500 Victor Roberts <xxx@xxxxxxxxxxxxxxxxxxxxx> wrote:

|>| Yes, as both Andrew and I, and perhaps others, have said.
|>| US-style instant start ballasts have nothing more than a
|>| high voltage transformer and a series inductor for current
|>| limiting, though the inductor is usually built into the
|>| transformer. They also usually have a power factor
|>| correcting capacitor across the input, but that does not
|>| change the answer.
|>
|>When you say the inductor is (usually) built into the transformer,
|>what does that mean? Is it just a convenience of integration, or
|>is it wired in some way that makes it necessary to be there?
|
| The inductor is not a separate part. There is no separate
| winding for the inductor. The transformer is designed so
| there is inductive leakage between the primary and
| secondary.

Then this is a design for which my question is not applicable.

The integrated transformer/inductor functions the same was
as the combination of a transformer and an inductor. Why
would this not be applicable to your design? You can also
use a separate transformer and inductor - it will work the
same way - I was only telling you how it is normally done in
commercial ballasts.

Well, maybe not. I'd like to see what kind of transformer design
this is to judge whether this is something relevant to what I am
seeking.

Go to www.uspto.gov and look at US 4,613,842. (I'm going to
try to attach a copy in pdf format but I'm not sure it will
come through on all news servers. If not I will post a link
to a copy on my web site.)

Figures 1 through 4 show rather conventional prior art
integrated transformer/inductors. In Figures 1 and 2 the
leakage inductance is created by the physical separation
between the windings. In Figures 3 and 4 the leg without any
windings but with the air gap provides a leakage inductance.
The designs shown in Figures 3 & 4 provide more leakage
inductance than the designs shown in Figures 1 & 2.

It's always hard to get an answer about an unconventional design
when everyone wants to steer me to a conventional design.

I don't think we are trying to steer you anywhere, but in
this case, the system, at least as you have described it so
far, is a conventional design.

|>Is the power factor correcting capacitor across the input at the
|>secondary of the transformer or the primary?
|
| When using a leaky transformer, the capacitor must be across
| the primary, since the virtual inductor is functionally
| "between" the primary and secondary.

And what if the current limit is just a classic magnetic inductor
and any transformer is autonomous (e.g. the light fixture system
only deals with AC power coming in at a certain voltage and does
not deal with how that voltage got there)?

Then the system works the same way.

|>What is the voltage involved here? How much higher beyond that can
|>it go safely, assuming the inductor, capacitor, and wiring, were all
|>made to handle that?
|
| You can go as high as you want, assuming, of course that all
| the wiring can withstand the voltage you choose. By the
| way, this is a hypothetical discussion. The voltages
| involved are all lethal. And the higher you go the more
| lethal they become. DO NOT TRY THIS UNLESS YOU UNDERSTAND
| THE RISKS INVOLVED WITH HIGH VOLTAGE CIRCUITS.

I sure won't be in any position to understand the risks as long
as I can't get an answer to what I am looking for.

I consider any voltage above the level at which the National
Electrical Code permits open conductors to be lethal (e.g.
Article 411). So even 120 volts is lethal. The issue with
even higher voltages can be a matter of degree, of course,
and a matter of whether they are contained within a fixture
or distributed within a structure.


|>What I'm looking for is a single voltage I can supply to a fixture
|>that with the appropriate inductive (magnetic) ballast designed for
|>that voltage and for the bulb/tube size/type, which will start it
|>and keep it running. And it to work on single pin cold cathode, too.
|>Is 480 volts enough? 600 volts? More? What if I limit the scope
|>of the goal to just smaller tubes? A list of voltages for each type
|>and size of tube would at least let me understand just how high it
|>has to go to support a selected range of them.
|
| Using only lamp types used in the US, I can say that the
| minimum open circuit voltage required ranges from 385 volts
| RMS for F40T12 lamps, to 565 volts for F96T12 lamps. The
| reference book I have is too old to have data for T8 or T5
| lamps or for CFLs. However, the voltage does go down as the
| length is reduced or the diameter is increased and goes up
| as the length is increased or the diameter is reduced.

I figured the voltage would go up with the length. I was not sure
about how the diameter affected it and was guessing it had more
influence on voltage drop than minimum open voltage (now that I
have a term others use for this concept, I might be able to get
more information I want).

So in theory, I could operate a fair range of lamp types directly
on 600 volts (commonly available in Canada, but not so common in the
USA) with just the magnetic inductor ballast designed for a 600 volt
source. Transformers to get 600 volts are readily available, so I
could do this either with a central 600 volt source (one big central
transformer converting my real source voltage to 600 volts) or with
individual sources (a small transformer to get 600 volts near or in
the actual fixture).

What I am also wanting to examine is the idea of designing a transformer
such that it's own impedance restricts the current where at the given
source voltage on the primary, the secondary voltage will provide the
strike voltage (or more) to an open circuit, and under load the voltage
will drop to the operating voltage (the voltage drop across the lamp)
at the level of current the lamp needs. It would, of course, be a
design that is specific to a particular lamp characteristic. Since
the transformer itself is now limiting the current, no further limiter
would be needed, so no ballast is needed; the conventional transformer
circuit would do the job.

See the patent listed above. However, note that a
transformer with its own impedance is no longer a
"conventional transformer."

Another common type of integrated transformer/inductor is
the common "neon sign transformer. These typically develop
at least 5000 volts but are internally current limited to
the rating of the sign using built0in leakage inductance.
Some I just found on the web have an open circuit voltage of
15,000 volts and the output current is limited to 30 ma in
one design and 60 ma in another.

What I am wondering about is what kind of
power factor would this result in.

The same as the equivalent separate transformer and inductor
and load.

--
Vic Roberts
http://www.RobertsResearchInc.com
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