Did the market price for tor go up? (c:
Just curious...
-- Al, the usual
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 AE6EO
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If anything, the general availability of toroids in the UK from broad line distribution has actually improved in recent years.
Graham
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.
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:
In alt.engineering.electrical Dave Platt 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: | |
They do have specialty uses, such as:
-- |---------------------------------------/----------------------------------| | 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 ----------------------------
|> |>Did the market price for tor go up? (c: |> | |> |
|> They do have specialty uses, such as: |>
|>
|> -- |> |---------------------------------------/----------------------------------| |> | Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below |> | |> | first name lower case at ipal.net / snipped-for-privacy@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 | |------------------------------------/-------------------------------------|
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
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
Seems like a good application for an NTC-thermistor inrush current limiter, with a few ohms of "cold" resistance?
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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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| James E.Thompson, P.E. | mens |
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I love to cook with wine. Sometimes I even put it in the food.
Absolutely. They work very well.
John
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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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
There's not a lot of thermal inertia in an NTC. How much slower than a lightbulb, say, is it really?
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.
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
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.
The absence of an air gap in toroids is a contributory factor to the problem btw.
Graham
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