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Old 20th May 2009, 08:05 PM   #1
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Default Tuna can shield

Any benefit to using a tuna can to shield a toroidal transformer?
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Old 20th May 2009, 08:15 PM   #2
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Default Re: Tuna can shield

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Originally posted by DynacoDave
Any benefit to using a tuna can to shield a toroidal transformer?

it's certainly prettier ..... especially if you leave original design on it

ok - there is slight shielding effect , too
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Old 20th May 2009, 08:37 PM   #3
Jeb-D. is offline Jeb-D.  United States
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I wonder which will shield better, Bumblebee or Chicken of the Sea?
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Old 20th May 2009, 10:04 PM   #4
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I would definitly go for the packed in oil .....
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Old 20th May 2009, 10:11 PM   #5
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boyz ....... don't make fun of serious question

there are benefits certainly , depending of material of which tuna can is made .
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Old 20th May 2009, 11:04 PM   #6
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Torroidals have a very 'controlled' flux leakage anyway.
You need to be careful that whatever can is used, it doesn't touch both the chassis and the transformer mounting bolt - as that is efectively a short circuited winding.
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Old 21st May 2009, 12:00 AM   #7
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All joking aside I seem to rember a discusion of this years ago.
The conclusion was that a thin metal shield like a tuna can won't
be verry effective as a shield. Besides it would hamper air flow
around the transformer and make it run hotter. And as was pointed out you should't have a lot of radiated fields from a toriod.
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Old 21st May 2009, 04:10 AM   #8
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Tuna cans are ideal for various things like holding cutting oil at the lathe. If you didn't do a good job of bypassing incoming RF on the mains cable, shielding the transformer might help contain it a bit. Or not. IMHO, toroids are over rated in their ability to magically contain stray magnetic flux. They still induce currents in nearby chassis metal, so they're not perfect, and magnetic shielding requires thicker metal and a full ring- just what you don't want with a toroid. The above mentioned heating is also an issue. I'd probably avoid the tuna can and rely on distance from sensitive circuitry, or go with a mu-metal shield supplied by the toroid manufacturer. OTOH, there's no harm in trying it. Just do some tests for temperature rise.
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Old 21st May 2009, 05:37 AM   #9
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I was , I think, worrying about the short circuited winding. I was under the impression toroidal radiated more than other types of transformers and that was a good reason to put them in an outboard power supply. Are there any good posts on torodals? My searches here have had limited results. Thanks for the info and, the levity .
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Old 27th May 2009, 10:44 PM   #10
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The metal of a typical tuna can has very low permability, which makes a lousy magnetic shield. Tuna cans work well from shielding tuna from the environment, not for magnetic shielding.

http://www.mushield.com/design-guide.shtml

As Eva has discussed in many previous posts, toriod emissions can be controlled by the way they are orientated when mounted on the circuit board.

E-core transformers can use a copper foil band (aka "hum band")installed around the outside of the transformer (parallel to the winding) and attached to ground that creates a current loop to attenuate emissions. However, since the external band is a current loop, it will reduce the efficiency and will decrease the maximum power load of the transformer.

A transformer with low leakage inductance should also help attenuate emissions. This is achived by keeping the close contact between the primary and secondary windings through the entire length of the transformer (ie bifilar, interleaving, etc). Unfortunately most pre-wound tranformers use a split bobbin to maximize isolation, but also maximizes inductance leakage, creating a noisy transformer.

BTW: Avoid eating tuna. Sea food is loaded with heavy metals cause by pollution. The US EPA now recommends limiting consumption of seafood meals to once a month.
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