Switching power supply for neon signs

[suraj]

Hello,

I am trying to design a switching power supply for neon signs. I know a
thing or two about ordinary smps designs ..... but in this particular
case.....15KV @ 30mA....the switching transformer design seems to be
difficult. Can someone help me on developing this power supply? I am
also looking for a person who can guide me in designing transformers.

Thank you in advance

 

[Winfield Hill]

suraj wrote...

I am trying to design a switching power supply for neon signs. I know
a thing or two about ordinary smps designs ..... but in this particular
case.....15KV @ 30mA....the switching transformer design seems to be
difficult. Can someone help me on developing this power supply? I am
also looking for a person who can guide me in designing transformers.

What is it you hope to do? Can we assume you plan on switching the
primary, rather than the secondary? If you use a 50/60Hz neon-
sign transformer, you'll have to use *low* switching frequencies, and
it shouldn't be too painful. On the other hand, if you want to design
and/or build a 450W 15kV high-frequency current-limiting transformer,
I can respectfully suggest that you don't have enough knowledge and
experience. If this is really what you want to do, then start with a
lower-power lower-voltage version to learn the ropes. Say 50W and 1kV.
Alternately, you may be able to find a commercially-available version
of a 100 to 450W 15kV smps neon-sign transformer. Let us know about
it if you do.

 

[Ancient_Hacker]

I'd go look at a catalog of replacement TV flyback transformers for
large projection TV's. Those generate a few watts at 20 to 30 KV.

They're NOT cheap, but much cheaper than the year or two it would take
the average person to figure out the technology for winding 10,000
turns of #40 wire without breaking and with the requisite insulation
and potting.


Then don't bother designing up a switfching power supply from scratch--
use an old PC power supply, they're available for nearly free. Just
piggyback your transformer onto one of those.

 

[Winfield Hill]

Ancient_Hacker wrote...

I'd go look at a catalog of replacement TV flyback transformers for
large projection TV's. Those generate a few watts at 20 to 30 KV.

They're NOT cheap, but much cheaper than the year or two it would
take the average person to figure out the technology for winding
10,000 turns of #40 wire without breaking and with the requisite
insulation and potting.

While I don't mean to imply winding HV transformers is easy, not
all require thousands of turns. For example, my own 10kV 300kHz
20kVA transformer has only 22 turns of #12 litz on its secondary,
and only one thick 1"-wide copper-strip turn on the primary, with
450V drive. It's very much a matter of the ferrite core.

 

[Genome]

Ancient_Hacker wrote...

While I don't mean to imply winding HV transformers is easy, not
all require thousands of turns. For example, my own 10kV 300kHz
20kVA transformer has only 22 turns of #12 litz on its secondary,
and only one thick 1"-wide copper-strip turn on the primary, with
450V drive. It's very much a matter of the ferrite core.

Oooooooh. That am sound like a big one!

DNA

 

[Spehro Pefhany]

Hello,

I am trying to design a switching power supply for neon signs. I know a
thing or two about ordinary smps designs ..... but in this particular
case.....15KV @ 30mA....the switching transformer design seems to be
difficult. Can someone help me on developing this power supply? I am
also looking for a person who can guide me in designing transformers.

Thank you in advance

I think normally the transformer secondary will be separated into
sections. There are standard bobbins that have the sections with
insulators molded in.

You're asking for a 450W CC supply. These things are pretty mature now
and are pretty cheap to buy-- if you're trying to come up with a
design for production you may wish to dissect a few commercial units
to see how they have made the transformers reliable long-term, there
are probably a few tricks that won't be obvious on the first pass.
Corona (the products of corona) eat(s) away at thin wires (and
enameled wire through pinholes) so you will likely have to coat or pot
the secondary.


Best regards,
Spehro Pefhany

 

[[email protected]]

Hello,

I am trying to design a switching power supply for neon signs. I know a
thing or two about ordinary smps designs ..... but in this particular
case.....15KV @ 30mA....the switching transformer design seems to be
difficult. Can someone help me on developing this power supply? I am
also looking for a person who can guide me in designing transformers.

Thank you in advance

Have you seen those piezoelectric transformers? At 5 watts each you
would need a whole whack of them ($5 each), but they're very compact (1
cm x 4 cm) and quite efficient. They resonate at 53 kHz and produce max
2.5 kV at a step-up ratio of around 60.

Search http://www.digikey.com for part number P6002-ND

 

[John Larkin]

Hello,

I am trying to design a switching power supply for neon signs. I know a
thing or two about ordinary smps designs ..... but in this particular
case.....15KV @ 30mA....the switching transformer design seems to be
difficult. Can someone help me on developing this power supply? I am
also looking for a person who can guide me in designing transformers.

Thank you in advance

There are lots of commercial switching-based "neon sign transformers"
around. They seem, to me, to produce a more diffuse looking light in
the tubes, less classical neon-looking. Maybe the glow is more uniform
across the cross-section of the tube with high-frequency drive.

John

 

[John Larkin]

There are lots of commercial switching-based "neon sign transformers"
around. They seem, to me, to produce a more diffuse looking light in
the tubes, less classical neon-looking. Maybe the glow is more uniform
across the cross-section of the tube with high-frequency drive.

John

This one is only $40, quantity 1. It might be useful for something or
other some day.

http://www.neoncentral.com/inventory.jsp?number=800-0151


John

 

[Ancient_Hacker]

Wow! I'm used to puny transformers that put out about 0.2 volts per
turn.

There really are cores that put out nearly twenty-five hundred times as
many volts per turn?

Arent you in danger of demagnetizing most of the East Coast with that
thing?

And I thought Tesla was pushing things with his lightning tower.

 

[John Fields]

There are lots of commercial switching-based "neon sign transformers"
around. They seem, to me, to produce a more diffuse looking light in
the tubes, less classical neon-looking. Maybe the glow is more uniform
across the cross-section of the tube with high-frequency drive.

 

[John Fields]

Wow! I'm used to puny transformers that put out about 0.2 volts per
turn.

---
Neon sign transformers are designed to saturate when their secondary
current reaches a design limit, and the impedances of their
primaries are designed to limit the input current to a value which
won't destroy the transformer when that happens, even if the output
is feeding a short.

Basically, what they're designed to do is to provide a voltage high
enough to strike an arc through a gas which presents a high
impedance prior to ionization and then, once the arc has been struck
and the load looks like a low impedance, to limit the current
through that load.

Essentially, a constant current transformer.
---

There really are cores that put out nearly twenty-five hundred times as
many volts per turn?

---
LOL, the primary isn't a single turn.
---

Arent you in danger of demagnetizing most of the East Coast with that
thing?

---
I wasn't aware that _our_ East Coast (if that's what you're talking
about) _was_ magnetized, but take a look at what it takes to make
the thing run:

Even with an output of 15000 volts, a load of 0.030 amperes = 450
watts and an efficiency of about 50%, It'll be taking less than a
kilowatt off of the grid, Not a great threat...
---

 

[linnix]

Hello,

I am trying to design a switching power supply for neon signs. I know a
thing or two about ordinary smps designs ..... but in this particular
case.....15KV @ 30mA....the switching transformer design seems to be
difficult. Can someone help me on developing this power supply? I am
also looking for a person who can guide me in designing transformers.

Thank you in advance

Are you sure it's 15KV? It's a pretty powerful neon signs. I am
familiar with 1KV neon, not with 15KV.

 

[John Fields]

Are you sure it's 15KV? It's a pretty powerful neon signs. I am
familiar with 1KV neon, not with 15KV.

 

[Spehro Pefhany]

Hmm.. that would indicate that neon transformers are rated in
short-circuit current, rather than full-load current, so the maximum
output of a 30mA 15kV supply is less than 250W.


Best regards,
Spehro Pefhany

 

[Fred Bloggs]

Ancient_Hacker wrote...



While I don't mean to imply winding HV transformers is easy, not
all require thousands of turns. For example, my own 10kV 300kHz
20kVA transformer has only 22 turns of #12 litz on its secondary,
and only one thick 1"-wide copper-strip turn on the primary, with
450V drive. It's very much a matter of the ferrite core.

I'm not sure the modern electronic drives even use a transformer. IIRC
it is a half-bridge drive of a resonant L-C to strike the arc, with the
neon in parallel with C, and then steady states to something approaching
more of a constant power drive.

 

[Joseph2k]

Ancient_Hacker wrote...

While I don't mean to imply winding HV transformers is easy, not
all require thousands of turns. For example, my own 10kV 300kHz
20kVA transformer has only 22 turns of #12 litz on its secondary,
and only one thick 1"-wide copper-strip turn on the primary, with
450V drive. It's very much a matter of the ferrite core.

Well said, too bad so many jumped on their swords in response.