Toroidal transformer mounting

Is there a minimum distance that one should leave around a toroid in a power supply? ie, how close to the edge of a case can it be?

I have an 81mm wide space in which I was hoping to mount a 77mm wide toroid.. Too tight, or fine?

Thanks!

Is it an encapsulated type?

Cheers

Ian

No, just something standard like this https://uk.farnell.com/block/rkd-40-2x12/transformer-2-x-12v-40va/dp/2362149

The only thing you need to be carefull about is that the bolt holding the transformer to chassis doesnt have any chance to make contact with the top panel if it did the  enclosure would form a  shorted turn on the transformer ,and a very large current would flow .

Tubetec said:

The only thing you need to be carefull about is that the bolt holding the transformer to chassis doesnt have any chance to make contact with the top panel if it did the  enclosure would form a  shorted turn on the transformer ,and a very large current would flow .

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Absolutely, I'm very aware of that and it certainly won't happen here. It's more the sides I was concerned about - there will be a gap, but it's likely to only be a couple of mm either side..

For UK mains the general rule is 3mm creepage/clearance so your 2mm gap is a little on the small side, however that is for naked wires. Since you toroid will be swathed in insulating material I do not think it will be an issue.

Cheers

ian

ruffrecords said:

For UK mains the general rule is 3mm creepage/clearance so your 2mm gap is a little on the small side, however that is for naked wires. Since you toroid will be swathed in insulating material I do not think it will be an issue.

Cheers

ian

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Wonderful!

personally, I would wire it up without bolting it down and then crank the gain and listen to the unit while moving the transformer with a glove. Then you actually know what's you're up against before bolting int down. that's just me though.

good luck,

Good advice from Builda ,
find the spot with least noise , I found tucked away  with the leads exiting into the corner of the chassis and closeby the mains earth/chassis safety ground  to be best , toroid sheilding tins can be found for  about 10 euros or less  on ebay ,cheap pressed steel with  powder coat . Using the chassis space/ other components  as much as possible to shield these is good ,extra shielding in the form of cans should help too . Allowing some space between the can and the transformer seems like a good plan ,It also allows extra concentric screening and insulation  to be added with everything grounding back to one point .

Keeping  the transformer  connecting leads long and well twisted together until you figure out the best mounting point might be a good plan .

Incidently, if the through bolt on a toroid comes into contact with chassis at both ends you actually form quite an efficient spot welder , the voltage spike will most likely fry any electronics  down the line too ;D