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Old 18th December 2005, 12:28 PM   #1
ash_dac is offline ash_dac  United Kingdom
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Default Mounting a torroidal transformer. (advice please)

Hi,

It's hard to find notes on the web on safely mounting torriodal tx's.

Just checking some things:-

-the bolt through the torroid should never touch the chassis ? (I think the core can go or is live)

-the on/off switch needs to be a dual switch to switch grnd, and live ?
(Is that there incase the cable is reveresed?)

-the chassis should be grounded (to stop the case going live)

-rubber on top, and bottom of core.

Any other safety issues?

I may opt for a chasis mount tx..


Kind regards,

Ashley.
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Old 18th December 2005, 12:42 PM   #2
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Hi Ashley

Quote:
-the bolt through the torroid should never touch the chassis ?


One end can touch, but not both.

Quote:
-the on/off switch needs to be a dual switch to switch grnd


You need to switch live and neutral, ground should remain connected at all times.

Quote:
--the chassis should be grounded


Very definately.

Quote:
--rubber on top, and bottom of core


Yes, to avoid mechanical damage to the windings causing shorts. And don't tighten the mounting bolt too much either.
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Old 18th December 2005, 12:49 PM   #3
ash_dac is offline ash_dac  United Kingdom
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Quote:
-the bolt through the torroid should never touch the chassis ?

One end can touch, but not both.
Thanks for the information.

Just one more thing:-

Any idea of mounting clearance above torroidal tx?


Kind regards,

Ashley.
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Old 18th December 2005, 12:53 PM   #4
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All depends on your chassis design and materials, but in general, 10mm or so should be more than enough.
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Old 2nd September 2006, 07:02 PM   #5
ash_dac is offline ash_dac  United Kingdom
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Hi,

About to order the stuff for a gainclone. I feel building the power supply should be done first.

This is the plan..

-Double throw switched fused rated for 5A
-Transformer primary wired to switch contacts
-Insulating sheath / boot covering live contacts
-Calculate correct slow blow fuse value
-Transformer bolted to case as per guidance.
-Ground connection to case (measure resitance to check safety)

Is it better to use fastons or solder on switches ?

Any other power supply safety tips ?
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Old 2nd September 2006, 07:17 PM   #6
poobah is offline poobah  United States
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I prefer the fastons... make sure the blade thickness is matched from blade to terminal.

Soldering is completely possible and would be more vibration resistant... not an issue here really. Sometimes switches and breakers can be damaged by the soldering heat. The switch will tell you what it wants. Faston spades means fastons... lugs mean soldering.

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Old 2nd September 2006, 08:46 PM   #7
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Best way is to insulate the bolt thats holding the toroid from ground and chassis......
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Old 2nd September 2006, 08:54 PM   #8
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> -the bolt through the torroid should never touch the chassis ?
>(I think the core can go or is live)
No, the core can't go live, and the bolt can directly touch the chassis. The important bit to remember is that you must NEVER allow a short circuit loop to form around the core; therefore, if the bolt is mounted on the chassis on one side, the other side must be free/unconnected. This isn't normally a problem if you just take the trafo, plus the two rubber sheets and the metal cover that are normally supplied, bolt it to the chassis and leave it alone otherwise.

>-the on/off switch needs to be a dual switch to switch grnd, and live ?
>(Is that there incase the cable is reveresed?)

For best safety, you should indeed switch both live and NEUTRAL. These are the two pins in a 2-prong mains plug. GROUND is the third, and it MUST NOT EVER be switched.

>-the chassis should be grounded (to stop the case going live)
Yup.

As for clearance, jus make sure nothing can make a short from the mounting bolt top to the chassis, and keep low-level signals away from the transformer. Other than that it's not critical.
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Old 3rd September 2006, 08:08 AM   #9
ash_dac is offline ash_dac  United Kingdom
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Question Do I need a power switch ?

Hi,


Thank you for the tips.

The Double throw switched and fused IEC inlet I can buy are suitable for class II applications but the fused IEC inlets I can get are suitable for class I applications.

Do I need a power switch?

Without a power switch I assume that at the electrical wall socket I will be switching very large currents.
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Old 3rd September 2006, 08:38 AM   #10
mzzj is offline mzzj  Finland
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Quote:
Originally posted by ash_dac
Hi,

-Ground connection to case (measure resitance to check safety)

Any other power supply safety tips ?
Scratch off any paint/oxidation under ground screw. Please note that if you have ANODIZED aluminium case it requires sometimes real heavy scrathing to remove anodization. (most pre-made 19" aluminium rack stuff is anodized for example.) Use "star washer" between ground wire lug and case. http://www.randyray.com/TMC/images/R...StarWasher.jpg

Use 2nd nut to make sure that ground connection cant became loose.
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