What happened to toroid power transformers?

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


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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.
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Dave Platt < snipped-for-privacy@radagast.org> AE6EO
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|>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
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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.
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Don Kelly snipped-for-privacy@shawcross.ca
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| |> | |> |------------------------------------/-------------------------------------| | | 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.
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Usual Suspect wrote:

If anything, the general availability of toroids in the UK from broad line distribution has actually improved in recent years.
Graham
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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.
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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 /
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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
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For those of us not familiar, 'splain, please?
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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
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Seems like a good application for an NTC-thermistor inrush current limiter, with a few ohms of "cold" resistance?
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On Tue, 13 Mar 2007 01:19:48 -0000, snipped-for-privacy@radagast.org (Dave Platt) wrote:

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

Absolutely. They work very well.
John
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On Tue, 13 Mar 2007 01:19:48 -0000, the renowned snipped-for-privacy@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.
Best regards, Spehro Pefhany
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On Mon, 12 Mar 2007 23:09:26 -0500, Spehro Pefhany

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
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On Mon, 12 Mar 2007 20:21:03 -0800, the renowned John Larkin

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
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Spehro Pefhany wrote:

John probably ought to speak to Plitron.
Graham
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There's not a lot of thermal inertia in an NTC. How much slower than a lightbulb, say, is it really?
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On Tue, 13 Mar 2007 04:24:23 GMT, the renowned "Homer J Simpson"

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
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