Tips for mount toroidal transformer

[Davebassman]

Hello,

can you tell me, how you do mount toroidal transformers into a rack enclosure?

I know, with the bolt, rubber pads and steel washer. But, for do it this way I need to drill the chassis and the bolt has a big head, and If you mount the rack into cabinet with other devices, this will be a problem with the bolt.

Any advice?

Thanks!!

[Enzo]

COuntersink the hole. If you look at commercial amps, you often see the bolt hole has an indentation in the bottom panel to clear the bolt head. And they use a carriage bolt - the bolt with the smooth slightly rounded head. But certainly a flat head bolt would work for limited clearance. You might countersink the hole for a bit more room.

IMPORTANT: if you run a bolt through the bottom panel of a metal enclosure through the toroid, DO NOT let the bolt be long enough to contact the top panel. If you let the bolt touch both top and bottom panels, it creates a "winding" through the toroid, a winding that is shorted end to end. This will have disastrous effect.

[dmeek]

I had an interesting repair on a homemade PA amp made with a toroidal transformer. The complaint was that it hummed, had always hummed.
The builder had connected the AC ground wire to a lug at the top of the mounting bolt making the ground circuit part of the transformer.
That was an easy fix. A nice memory this week when I have some really tough ones.

[Mick Bailey]

If you swap the bolt out for a countersunk one you can do a 'formed countersink' in the chassis. The easiest way to form this is to use an allen head high tensile bolt about 1.5" long. On the inside of the chassis use a spacer with a bore about 3/16" greater than the head diameter of the bolt (you can use a large nut or stack of washers) and then use a thick washer over this with the same bore as the thread. Centre it up and thread on a nut. With an allen key one side and socket wrench the other tighten it up until the countersink head of the bolt pulls in level. A kind of DIY press tooling. This gives a secure seating in the sheet metal for the actual bolt which is to be used.

It helps to mark the inside of the chassis with a gide so that you can see that everything is centred.

It sounds involved but is quick to do, like using a chassis punch.