Electrical Engineering - What happened to toroid power transformers?

Author

What happened to toroid power transformers?

Usual Suspect

2007-03-08, 5:25 pm

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

2007-03-08, 5:25 pm

>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

2007-03-08, 5:25 pm

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

2007-03-08, 5:25 pm

"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.

2007-03-09, 1:25 pm

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/

phil-news-nospam@ipal.net

2007-03-09, 5:25 pm

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/in...mrs/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

2007-03-09, 9:25 pm

<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/in...mrs/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
----------------------------

phil-news-nospam@ipal.net

2007-03-12, 5:25 pm

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/in...mrs/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

2007-03-12, 8:25 pm

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.

2007-03-12, 8:25 pm

> 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

2007-03-12, 8:25 pm

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

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

2007-03-12, 8:25 pm

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

>
>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

2007-03-12, 9:25 pm

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:
>
>
>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 Voice

480)460-2350 | |
| E-mail Address at Website Fax

John Larkin

2007-03-13, 3:25 am

Spehro Pefhany

2007-03-13, 3:25 am

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:
>
>
>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

John Larkin

2007-03-13, 3:25 am

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:
>
>
>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

Homer J Simpson

2007-03-13, 3:25 am

"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

2007-03-13, 3:25 am

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

2007-03-13, 3:25 am

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:
>
>
>
> 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

2007-03-13, 3:25 am

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...
>
>
>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

Spehro Pefhany

2007-03-13, 3:25 am

On Mon, 12 Mar 2007 20:21:03 -0800, the renowned John Larkin
<jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

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

You didn't happen to measure the current peaks before and after, did
you? Probably not or you'd say so. That would be an interesting bit of
info.

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

Eeyore

2007-03-13, 3:25 am

John Larkin wrote:

> John E. <incognito@yahoo.com> wrote:
>
>
> A conventional laminated core has corners and stuff.

It also has a small distributed air gap.

> 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, you can fix this by running toroids at a *lower* flux or you can fit an
inrush current limiting device / circuit.

The absence of an air gap in toroids is a contributory factor to the problem
btw.

Graham

Eeyore

2007-03-13, 3:25 am

Spehro Pefhany wrote:

> What happens if the power blips with the NTC hot?

You hope the PSU filter caps hold up !

Graham

Eeyore

2007-03-13, 3:25 am

Winfield Hill wrote:

> John Larkin wrote:
>
> 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.

In which case you'd probably like R-cores and O-cores even more.

Graham

Eeyore

2007-03-13, 3:25 am

Paul Mathews wrote:

> John Larkin wrote:
>
> Other approaches commonly taken include a series power resistor
> shunted by relay contacts or a triac turned on after a delay.

The omly reason I've never done that is the issue of dissipation in the triac.

> Another approach is to use SCRs in 2 legs of the secondary bridge rectifier,
> using phase control to ramp up the secondary current.

A certain designer uses that technique to modulate the output voltage.

Graham

Eeyore

2007-03-13, 3:25 am

Spehro Pefhany wrote:

> John Larkin wrote:
>
>
> You didn't happen to measure the current peaks before and after, did
> you? Probably not or you'd say so. That would be an interesting bit of
> info.

John probably ought to speak to Plitron.

Graham

Winfield Hill

2007-03-13, 9:25 am

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 poorer line-to-output AC isolation the conventional
types with separated split windings. They usually have lower
leakage inductance, which is bad for direct bridge-rectifier
storage-capacitor setups as it leads to higher peak currents.
Plus, they don't welcome adding a grounded primary-secondary
inter-winding shield. But hey, what the hell, I like their
low ac magnetic fields spreading into sensitive electronics.

Eeyore

2007-03-13, 9:25 am

Winfield Hill wrote:

> John Larkin wrote:
>
> They have poorer line-to-output AC isolation the conventional
> types with separated split windings. They usually have lower
> leakage inductance, which is bad for direct bridge-rectifier
> storage-capacitor setups as it leads to higher peak currents.
> Plus, they don't welcome adding a grounded primary-secondary
> inter-winding shield. But hey, what the hell, I like their
> low ac magnetic fields spreading into sensitive electronics.

R-cores are vastly better.

Graham

John Larkin

2007-03-13, 1:25 pm

On 12 Mar 2007 22:06:44 -0700, "Paul Mathews" <opto@whidbey.com>
wrote:

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

In one of our products, we use a primary-side resistor-triac as both a
surge limiter and a crude bang-bang regulator, to reduce the stress on
downstream stuff as line voltage changes.

John

John Larkin

2007-03-13, 1:25 pm

On 12 Mar 2007 21:59:12 -0700, "Winfield Hill" <hill@rowland.org>
wrote:

>John Larkin wrote:
>
> 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.

This was for an nmr gradient amp, in a rack with lots of stuff that
doesn't like 60 Hz fields. We finally talked them into letting us use
switchers - it took about 10 years - and they work great.

John

Terry Given

2007-03-13, 5:25 pm

Eeyore wrote:
>
> John Larkin wrote:
>
>
>
>
> It also has a small distributed air gap.
>
>
>
>
>
> John, you can fix this by running toroids at a *lower* flux or you can fit an
> inrush current limiting device / circuit.
>

yeah, but it has to be 50% of Bsat, or the problem still occurs.

So Np doubles.

And given a full winding window, Rp quadruples.

> The absence of an air gap in toroids is a contributory factor to the problem
> btw.
>
> Graham

I've since sold it, but I used to have a little 100kVA transformer I
bought for $200, brand new. It ran at 250mT peak flux density. was
designed for a motor test application, where it was switched on & off
about once per minute, hence the tiny Bpeak. but the customer went broke
and never picked it up, so it sat in the factory for several years,
until I came along.

I ended up selling it for $1000 ;)

damn shame though, I could use it now

Cheers
Terry

John E.

2007-03-16, 3:25 am

> In one of our products, we use a primary-side resistor-triac as both a
> surge limiter and a crude bang-bang regulator, to reduce the stress on
> downstream stuff as line voltage changes.

Diagram, please (c:
--
John English

Joerg

2007-03-16, 1:25 pm

Winfield Hill wrote:

> John Larkin wrote:
>
>
>
> They have poorer line-to-output AC isolation the conventional
> types with separated split windings. They usually have lower
> leakage inductance, which is bad for direct bridge-rectifier
> storage-capacitor setups as it leads to higher peak currents.
> Plus, they don't welcome adding a grounded primary-secondary
> inter-winding shield. But hey, what the hell, I like their
> low ac magnetic fields spreading into sensitive electronics.
>

We use toroids almost exclusively for medical. A shield layer is no
problem at all. I also use them here in the office and in the lab for
120V/230V conversion because they are almost completely silent.

--
Regards, Joerg

http://www.analogconsultants.com

Lostgallifreyan

2007-03-16, 5:25 pm

Joerg <notthisjoergsch@removethispacbell.net> wrote in
news:uryKh.8079$Um6.6155@newssvr12.news.prodigy.net:

> Winfield Hill wrote:
>
>
> We use toroids almost exclusively for medical. A shield layer is no
> problem at all. I also use them here in the office and in the lab for
> 120V/230V conversion because they are almost completely silent.
>

While following this thread, I saw a couple of people mention R-cores.
Would they not be better?

I'd once seen one and thought it was some eccentric variant on a toroid
that someone made so they could mount it where their design once called for
a chassis mounted E/I type, or had some other odd space restriction. I was
so wrong.

From what I saw via Google once I'd seen the name 'R-core', I see that easy
fitting of split bobbins directly round the straight long sections allows
either a commercial firm OR a hobbyist to not only build their windings
quickly and easily, but to modify them, as an assembled bobbin can rotate
freely if wanted. Electrical isolation between windings can be better than
in a toroidal type, which could be important for use in a medical device.
The efficiency is good, and the flux well-contained, and they'd probably
run as quietly as toroidals. Waste heat can escape from them more
efficiently that either E/I types or toroidals. I'm surprised they aren't
much more widespread than toroidals.

Joerg

2007-03-16, 5:25 pm

Lostgallifreyan wrote:

> Joerg <notthisjoergsch@removethispacbell.net> wrote in
> news:uryKh.8079$Um6.6155@newssvr12.news.prodigy.net:
>
>
>
>
> While following this thread, I saw a couple of people mention R-cores.
> Would they not be better?
>
> I'd once seen one and thought it was some eccentric variant on a toroid
> that someone made so they could mount it where their design once called for
> a chassis mounted E/I type, or had some other odd space restriction. I was
> so wrong.

>
> From what I saw via Google once I'd seen the name 'R-core', I see that easy
> fitting of split bobbins directly round the straight long sections allows
> either a commercial firm OR a hobbyist to not only build their windings
> quickly and easily, but to modify them, as an assembled bobbin can rotate
> freely if wanted. Electrical isolation between windings can be better than
> in a toroidal type, which could be important for use in a medical device.
> The efficiency is good, and the flux well-contained, and they'd probably
> run as quietly as toroidals. Waste heat can escape from them more
> efficiently that either E/I types or toroidals. I'm surprised they aren't
> much more widespread than toroidals.

They used to be quite popular in TV sets. I believe I still have a few
cores. Nowadays often just called U-U cores. For those who haven't seen
them yet:
http://www.electroassemblies.com/r-core.htm

One challenge with these is proper clamping. You can't inspect how snug
the core halves are joining because it is inside the packets.

BTW your follow-up settings aren't right, was missing three NGs. That
would have broken the thread for those folks.

--
Regards, Joerg

http://www.analogconsultants.com

Eeyore

2007-03-16, 5:25 pm

Joerg wrote:

> Lostgallifreyan wrote:

Expensive ! You also can't bump up the copper as you can with a toroid.

[color=darkred]
> They used to be quite popular in TV sets.

??????

> I believe I still have a few cores. Nowadays often just called U-U cores.

Not the same thing at all.

> For those who haven't seen
> them yet:
> http://www.electroassemblies.com/r-core.htm
>
> One challenge with these is proper clamping. You can't inspect how snug
> the core halves are joining because it is inside the packets.

An R-core is made from continuous strip like a toroid. No clamping is invoved.

Graham

Joerg

2007-03-16, 5:25 pm

Eeyore wrote:

>
> Joerg wrote:
>
>
>
>
> Expensive ! You also can't bump up the copper as you can with a toroid.
>
>
>
>
>
> ??????
>
>
>
>
>
> Not the same thing at all.
>
>
>
>
>
> An R-core is made from continuous strip like a toroid. No clamping is invoved.
>

Hmm, so how does that make winding easier then?

--
Regards, Joerg

http://www.analogconsultants.com

Eeyore

2007-03-16, 5:25 pm

Joerg wrote:

> Eeyore wrote:
>
> Hmm, so how does that make winding easier then?

Only easier with the correct machinery.

The formers are made in 2 pieces that clip together and the winding machine spins
the bobbins on the limbs of the core. The bobbins have 'gear teeth' to engage with
the winding machine.

Graham

Lostgallifreyan

2007-03-16, 5:25 pm

Joerg <notthisjoergsch@removethispacbell.net> wrote in
news:%jCKh.10629$jx3.8853@newssvr25.news.prodigy.net:

> Hmm, so how does that make winding easier then?
>

It does if you can wind the bobbin round the former it's clamped round.

Eeyore wrote:

>
>
> Expensive ! You also can't bump up the copper as you can with a toroid.

What does 'bump up' mean? Re expense, if the bobbin can be rotated round
the straight part of the former it's built onto, it would be a lot less
awkward than winding a toroid, it would not be much more awkward that
winding onto any spool. So why would it be more expensive than a toroid,
given that the former is made the same way, and the windings are easier to
wind?

Joerg

2007-03-16, 8:25 pm

Eeyore wrote:

>
> Joerg wrote:
>
>
>
>
> Only easier with the correct machinery.
>
> The formers are made in 2 pieces that clip together and the winding machine spins
> the bobbins on the limbs of the core. The bobbins have 'gear teeth' to engage with
> the winding machine.
>

Ah, thanks. To be honest I have never seen one. But it sure looks like a
cool trick.

--
Regards, Joerg

http://www.analogconsultants.com

LinkBot