What happened to toroid power transformers?

[Usual Suspect]

15 years ago there were (if I remember correctly) lots of toroid power
transformers available. It seems that most of what is available now is the
same old steel lam cores.

Did the market price for tor go up? (c:

Just curious...
--
Al, the usual

 

[Dave Platt]

15 years ago there were (if I remember correctly) lots of toroid power
transformers available. It seems that most of what is available now is the
same old steel lam cores.

Did the market price for tor go up? (c:

www.toroid.com
www.avellindberg.com
www.amveco.com
www.plitron.com
www.nuvotem.com
www.atc-frost.com

Mouser Electronics carries Hammond toroidal power transformers.

I don't know whether toroidal power transformers are more or less
common than 15 years ago. They always seem to have been a specialty
item, with higher costs than EI-core or similar traditional types.

--
Dave Platt <dplatt@radagast.org> AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

 

[Eeyore]

Usual Suspect wrote:

15 years ago there were (if I remember correctly) lots of toroid power
transformers available. It seems that most of what is available now is the
same old steel lam cores.

If anything, the general availability of toroids in the UK from broad line
distribution has actually improved in recent years.

Graham

 

[Charles Schuler]

"Usual Suspect" <reply@thegroup.net> wrote in message
news:0001HW.C215A7280046CB0AF01826C8@news.sf.sbcglobal.net...

15 years ago there were (if I remember correctly) lots of toroid power
transformers available. It seems that most of what is available now is the
same old steel lam cores.

Did the market price for tor go up? (c:

Just curious...

I'll guess that since they cost more, designers are opting for less
expensive types. Also, thanks to switch-mode power supplies, the market is
shrinking for line transformers.

 

[Ed]

There are many advantages to using this type of transformer.

I've been cleaning out lots of parts after years of building and have
a few for sale.

They are listed in the 'parts for sale' page on my web site at:

http://mysite.verizon.net/topossibilities/

 

In alt.engineering.electrical Dave Platt <dplatt@radagast.org> wrote:
|>15 years ago there were (if I remember correctly) lots of toroid power
|>transformers available. It seems that most of what is available now is the
|>same old steel lam cores.
|>
|>Did the market price for tor go up? (c:
|
| www.toroid.com
| www.avellindberg.com
| www.amveco.com
| www.plitron.com
| www.nuvotem.com
| www.atc-frost.com
|
| Mouser Electronics carries Hammond toroidal power transformers.
|
| I don't know whether toroidal power transformers are more or less
| common than 15 years ago. They always seem to have been a specialty
| item, with higher costs than EI-core or similar traditional types.

They do have specialty uses, such as:

http://www.equitech.com/products/industrial/xfmrs/toroid.html
http://www.equitech.com/products/industrial/wall.html

--
|---------------------------------------/----------------------------------|
| Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below |
| first name lower case at ipal.net / spamtrap-2007-03-09-1651@ipal.net |
|------------------------------------/-------------------------------------|

 

[Don Kelly]

<phil-news-nospam@ipal.net> wrote in message
news:essoen01ndl@news3.newsguy.com...

In alt.engineering.electrical Dave Platt <dplatt@radagast.org> wrote:
|>15 years ago there were (if I remember correctly) lots of toroid power
|>transformers available. It seems that most of what is available now is
the
|>same old steel lam cores.
|
|>Did the market price for tor go up? (c:
|
| www.toroid.com
| www.avellindberg.com
| www.amveco.com
| www.plitron.com
| www.nuvotem.com
| www.atc-frost.com
|
| Mouser Electronics carries Hammond toroidal power transformers.
|
| I don't know whether toroidal power transformers are more or less
| common than 15 years ago. They always seem to have been a specialty
| item, with higher costs than EI-core or similar traditional types.

They do have specialty uses, such as:

http://www.equitech.com/products/industrial/xfmrs/toroid.html
http://www.equitech.com/products/industrial/wall.html

--
|---------------------------------------/----------------------------------|
| Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below
|
| first name lower case at ipal.net / spamtrap-2007-03-09-1651@ipal.net
|
|------------------------------------/-------------------------------------|

Possibly the toroidal transformers that the original poster was referring to
were "pole pig" traansformers rather than the more specialized (isolation?
,auto?) transformers indicated by your references. These were/are(?) made
but are considerably larger than the units shown.
--

Don Kelly dhky@shawcross.ca
remove the X to answer
----------------------------

 

In alt.engineering.electrical Don Kelly <dhky@shaw.ca> wrote:
| <phil-news-nospam@ipal.net> wrote in message
| news:essoen01ndl@news3.newsguy.com...
|> In alt.engineering.electrical Dave Platt <dplatt@radagast.org> wrote:
|> |>15 years ago there were (if I remember correctly) lots of toroid power
|> |>transformers available. It seems that most of what is available now is
|> the
|> |>same old steel lam cores.
|> |>
|> |>Did the market price for tor go up? (c:
|> |
|> | www.toroid.com
|> | www.avellindberg.com
|> | www.amveco.com
|> | www.plitron.com
|> | www.nuvotem.com
|> | www.atc-frost.com
|> |
|> | Mouser Electronics carries Hammond toroidal power transformers.
|> |
|> | I don't know whether toroidal power transformers are more or less
|> | common than 15 years ago. They always seem to have been a specialty
|> | item, with higher costs than EI-core or similar traditional types.
|>
|> They do have specialty uses, such as:
|>
|> http://www.equitech.com/products/industrial/xfmrs/toroid.html
|> http://www.equitech.com/products/industrial/wall.html
|>
|> --
|> |---------------------------------------/----------------------------------|
|> | Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below
|> |
|> | first name lower case at ipal.net / spamtrap-2007-03-09-1651@ipal.net
|> |
|> |------------------------------------/-------------------------------------|
|
| Possibly the toroidal transformers that the original poster was referring to
| were "pole pig" traansformers rather than the more specialized (isolation?
| ,auto?) transformers indicated by your references. These were/are(?) made
| but are considerably larger than the units shown.

I've never seen one of those. But that would be interesting.

--
|---------------------------------------/----------------------------------|
| Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below |
| first name lower case at ipal.net / spamtrap-2007-03-12-1511@ipal.net |
|------------------------------------/-------------------------------------|

 

[John Larkin]

On Thu, 08 Mar 2007 19:39:47 GMT, Usual Suspect <reply@thegroup.net>
wrote:

15 years ago there were (if I remember correctly) lots of toroid power
transformers available. It seems that most of what is available now is the
same old steel lam cores.

Did the market price for tor go up? (c:

Just curious...

We use toroidal power transformers in some of our products. They're
small, don't leak much field, and don't cost much more than regular
ones. But they are sure hard on line fuses.

John

 

[John E.]

We use toroidal power transformers in some of our products. They're
small, don't leak much field, and don't cost much more than regular
ones. But they are sure hard on line fuses.

John

For those of us not familiar, 'splain, please?
--
John English

 

[John Larkin]

On Tue, 13 Mar 2007 00:24:45 GMT, John E. <incognito@yahoo.com> wrote:

We use toroidal power transformers in some of our products. They're
small, don't leak much field, and don't cost much more than regular
ones. But they are sure hard on line fuses.

John

For those of us not familiar, 'splain, please?

A conventional laminated core has corners and stuff. Some parts run at
lower flux density than others, so are sort of buffers against hard
saturation. Toroids have nice uniform cores, so can be designed to
have all of the core material run near saturation. That's one reason
they are so small and light. The geometry favors low copper
resistance, too.

So switch off a piece of gear that uses a toroidal line transformer.
If you're unlucky, the switchoff will happen at maximum flux density
in one direction, and leave some residual magnetization. Now, more bad
luck, turn it on at the ac zero crossing in the same direction. All
the core saturates and a huge primary current flows. This cheerfully
takes out mdl or even slo-blow fuses, and sometimes power switches.
We've measured 1000 amp peaks on modest-sized transformers, and you
could hear the wiring jump inside the wall.

CE requirements don't allow over-rating fuses a lot, so that can be
really nasty. The super-slow TT fuses help, but are sometimes hard to
get.

John

 

[Dave Platt]

In article <gtsbv2923v8c5p7oevdl4r3f081c66nt3t@4ax.com>,
John Larkin <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

For those of us not familiar, 'splain, please?

A conventional laminated core has corners and stuff. Some parts run at
lower flux density than others, so are sort of buffers against hard
saturation. Toroids have nice uniform cores, so can be designed to
have all of the core material run near saturation. That's one reason
they are so small and light. The geometry favors low copper
resistance, too.

So switch off a piece of gear that uses a toroidal line transformer.
If you're unlucky, the switchoff will happen at maximum flux density
in one direction, and leave some residual magnetization. Now, more bad
luck, turn it on at the ac zero crossing in the same direction. All
the core saturates and a huge primary current flows. This cheerfully
takes out mdl or even slo-blow fuses, and sometimes power switches.
We've measured 1000 amp peaks on modest-sized transformers, and you
could hear the wiring jump inside the wall.

Seems like a good application for an NTC-thermistor inrush current
limiter, with a few ohms of "cold" resistance?

--
Dave Platt <dplatt@radagast.org> AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

 

[Jim Thompson]

On Tue, 13 Mar 2007 01:19:48 -0000, dplatt@radagast.org (Dave Platt)
wrote:

In article <gtsbv2923v8c5p7oevdl4r3f081c66nt3t@4ax.com>,
John Larkin <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

For those of us not familiar, 'splain, please?

A conventional laminated core has corners and stuff. Some parts run at
lower flux density than others, so are sort of buffers against hard
saturation. Toroids have nice uniform cores, so can be designed to
have all of the core material run near saturation. That's one reason
they are so small and light. The geometry favors low copper
resistance, too.

So switch off a piece of gear that uses a toroidal line transformer.
If you're unlucky, the switchoff will happen at maximum flux density
in one direction, and leave some residual magnetization. Now, more bad
luck, turn it on at the ac zero crossing in the same direction. All
the core saturates and a huge primary current flows. This cheerfully
takes out mdl or even slo-blow fuses, and sometimes power switches.
We've measured 1000 amp peaks on modest-sized transformers, and you
could hear the wiring jump inside the wall.

Seems like a good application for an NTC-thermistor inrush current
limiter, with a few ohms of "cold" resistance?

I used to use NTC-thermistors at GenRad until some weisenheimer came
by and toggled the ON/OFF switch at a rapid rate and blew my PS all to
hell.

So I rigged it so that turning OFF forced a 15-second wait before ON
would function ;-)

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice480)460-2350 | |
| E-mail Address at Website Fax480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.

 

[John Larkin]

On Tue, 13 Mar 2007 01:19:48 -0000, dplatt@radagast.org (Dave Platt)
wrote:

In article <gtsbv2923v8c5p7oevdl4r3f081c66nt3t@4ax.com>,
John Larkin <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

For those of us not familiar, 'splain, please?

A conventional laminated core has corners and stuff. Some parts run at
lower flux density than others, so are sort of buffers against hard
saturation. Toroids have nice uniform cores, so can be designed to
have all of the core material run near saturation. That's one reason
they are so small and light. The geometry favors low copper
resistance, too.

So switch off a piece of gear that uses a toroidal line transformer.
If you're unlucky, the switchoff will happen at maximum flux density
in one direction, and leave some residual magnetization. Now, more bad
luck, turn it on at the ac zero crossing in the same direction. All
the core saturates and a huge primary current flows. This cheerfully
takes out mdl or even slo-blow fuses, and sometimes power switches.
We've measured 1000 amp peaks on modest-sized transformers, and you
could hear the wiring jump inside the wall.

Seems like a good application for an NTC-thermistor inrush current
limiter, with a few ohms of "cold" resistance?

Absolutely. They work very well.

John

 

[John Larkin]

On Mon, 12 Mar 2007 23:09:26 -0500, Spehro Pefhany
<speffSNIP@interlogDOTyou.knowwhat> wrote:

On Tue, 13 Mar 2007 01:19:48 -0000, the renowned dplatt@radagast.org
(Dave Platt) wrote:

In article <gtsbv2923v8c5p7oevdl4r3f081c66nt3t@4ax.com>,
John Larkin <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

For those of us not familiar, 'splain, please?

A conventional laminated core has corners and stuff. Some parts run at
lower flux density than others, so are sort of buffers against hard
saturation. Toroids have nice uniform cores, so can be designed to
have all of the core material run near saturation. That's one reason
they are so small and light. The geometry favors low copper
resistance, too.

So switch off a piece of gear that uses a toroidal line transformer.
If you're unlucky, the switchoff will happen at maximum flux density
in one direction, and leave some residual magnetization. Now, more bad
luck, turn it on at the ac zero crossing in the same direction. All
the core saturates and a huge primary current flows. This cheerfully
takes out mdl or even slo-blow fuses, and sometimes power switches.
We've measured 1000 amp peaks on modest-sized transformers, and you
could hear the wiring jump inside the wall.

Seems like a good application for an NTC-thermistor inrush current
limiter, with a few ohms of "cold" resistance?

What happens if the power blips with the NTC hot? Short blips in AC
power are pretty common, and there would be negligible time for the
NTC to cool.

We were concerned about that, and did some tests, on a 1000 watt CAMAC
crate power supply. It ate power switches before we installed NTCs,
and after that was fine. We tried teasing the power switch all sorts
of ways, and it still worked. Ditto on an NMR gradient driver. Don't
quite understand why.

John

 

[Spehro Pefhany]

On Tue, 13 Mar 2007 01:19:48 -0000, the renowned dplatt@radagast.org
(Dave Platt) wrote:

In article <gtsbv2923v8c5p7oevdl4r3f081c66nt3t@4ax.com>,
John Larkin <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

For those of us not familiar, 'splain, please?

A conventional laminated core has corners and stuff. Some parts run at
lower flux density than others, so are sort of buffers against hard
saturation. Toroids have nice uniform cores, so can be designed to
have all of the core material run near saturation. That's one reason
they are so small and light. The geometry favors low copper
resistance, too.

So switch off a piece of gear that uses a toroidal line transformer.
If you're unlucky, the switchoff will happen at maximum flux density
in one direction, and leave some residual magnetization. Now, more bad
luck, turn it on at the ac zero crossing in the same direction. All
the core saturates and a huge primary current flows. This cheerfully
takes out mdl or even slo-blow fuses, and sometimes power switches.
We've measured 1000 amp peaks on modest-sized transformers, and you
could hear the wiring jump inside the wall.

Seems like a good application for an NTC-thermistor inrush current
limiter, with a few ohms of "cold" resistance?

What happens if the power blips with the NTC hot? Short blips in AC
power are pretty common, and there would be negligible time for the
NTC to cool.


Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
speff@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com

 

[Homer J Simpson]

"Spehro Pefhany" <speffSNIP@interlogDOTyou.knowwhat> wrote in message
news:gq8cv214apokhpgioo9iiql0uggacdcvaf@4ax.com...

What happens if the power blips with the NTC hot? Short blips in AC
power are pretty common, and there would be negligible time for the
NTC to cool.

There's not a lot of thermal inertia in an NTC. How much slower than a
lightbulb, say, is it really?

 

[Winfield Hill]

John Larkin wrote:

We use toroidal power transformers in some of our products. They're
small, don't leak much field, and don't cost much more than regular
ones. But they are sure hard on line fuses.

They have poor line-to-output AC isolation. They usually have low
leakage inductance, that's bad for direct bridge-rectifier storage-
capacitor setups. Plus, it's not so easy to add a grounded primary-
secondary inter-winding shield. But hey, what the hell, I like 'em.
Low ac magnetic fields spreading out into my sensitive electronics.

 

[Paul Mathews]

On Mar 12, 5:58 pm, John Larkin
<jjlar...@highNOTlandTHIStechnologyPART.com> wrote:

On Tue, 13 Mar 2007 00:24:45 GMT, John E. <incogn...@yahoo.com> wrote:
We use toroidal power transformers in some of our products. They're
small, don't leak much field, and don't cost much more than regular
ones. But they are sure hard on line fuses.

John

For those of us not familiar, 'splain, please?

A conventional laminated core has corners and stuff. Some parts run at
lower flux density than others, so are sort of buffers against hard
saturation. Toroids have nice uniform cores, so can be designed to
have all of the core material run near saturation. That's one reason
they are so small and light. The geometry favors low copper
resistance, too.

So switch off a piece of gear that uses a toroidal line transformer.
If you're unlucky, the switchoff will happen at maximum flux density
in one direction, and leave some residual magnetization. Now, more bad
luck, turn it on at the ac zero crossing in the same direction. All
the core saturates and a huge primary current flows. This cheerfully
takes out mdl or even slo-blow fuses, and sometimes power switches.
We've measured 1000 amp peaks on modest-sized transformers, and you
could hear the wiring jump inside the wall.

CE requirements don't allow over-rating fuses a lot, so that can be
really nasty. The super-slow TT fuses help, but are sometimes hard to
get.

John

Other approaches commonly taken include a series power resistor
shunted by relay contacts or a triac turned on after a delay. Another
approach is to use SCRs in 2 legs of the secondary bridge rectifier,
using phase control to ramp up the secondary current. This often
works, since part of the turn-on surge....sometimes a big share of
it....is actually the charging current for the secondary side
capacitors reflected back to the primary side, with very little
leakage inductance in series. ST makes a part designed to switch the
line at zero crossings.

Paul Mathews

 

[Spehro Pefhany]

On Tue, 13 Mar 2007 04:24:23 GMT, the renowned "Homer J Simpson"
<nobody@nowhere.com> wrote:

"Spehro Pefhany" <speffSNIP@interlogDOTyou.knowwhat> wrote in message
news:gq8cv214apokhpgioo9iiql0uggacdcvaf@4ax.com...

What happens if the power blips with the NTC hot? Short blips in AC
power are pretty common, and there would be negligible time for the
NTC to cool.

There's not a lot of thermal inertia in an NTC. How much slower than a
lightbulb, say, is it really?

Typical momentary power blip is perhaps 100msec. The thermistor won't
change temperature much in that length of time- just look at it, and
consider the relatively low operating temperature. Or check a data
sheet.. the thermal time constant for the SL22 0R712 is 94 seconds!


Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
speff@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com