Squeezing in a toroid

[jeff mai]

I have a toroid. I have a chassis. The toroid fits inside, but only without the mounting plate. I do not want to alter the chassis. I do not want to use a different toroid.

Any suggestions on mounting without using the plate?

An intriguing alternative I saw when searching was to use epoxy to fill the center of the toroid and then drill a hole through the set epoxy for the mounting bolt. In practice, I'm not certain how well this would work.

[carlosfm]

The plate is thin, doesn't it fit?
Cut the bolt at the right length, it could be made not to pass the plate's top.

[jeff mai]

Originally posted by carlosfm
The plate is thin, doesn't it fit?

No, it doesn't fit. The toroid without the plate fits with only about 1mm clearance.

[carlosfm]

With some holes in the bottom of the chassis you could use some plastic bracers (is this the right english word?) to secure the toroid.

[hifi]

Maybe you can do something like this?



Be carefull not to short the magnetic field around the toroid as it would make the core crack (O_O)

I.e dont let the case and mounting bolt make a closed path around the transformer.

/Mikael

[jeff mai]

Originally posted by hifi
Maybe you can do something like this?

Yes, that's what I was thinking.

What sort of epoxy would I want to use, I wonder?

I know about avoiding a shorted turn.

Thanks,

Jeff

[chipco3434]

What sort of epoxy would I want to use, I wonder?

I use a product called WEST SYSTEM from Gudgeon Brothers for marine applications. I generally use a SLOW rated hardener. A boating store is a good place to look for these products.

What ever you use, don't try that pour in a single step using just epoxy at room temperature. With 40 or 50 cubic cm in one shot, the epoxy will get VERY, VERY hot in a few minutes time. It would most likely exotherm ~ results will be smoke & foam.

You might make it one pour if you were to 1) chill or freeze the toroid 2) mix a filler with the epoxy (~colloidal silica or micro balloons or sand) 3) refrigerate during cure. The point is that you most likely just can't pour it un one slug without doing something a little special.

[SheldonD]

This epoxy fill method what plitron uses.

You should not have to to fill all of the "hole in the doughnut"

Epoxy does not bond to polyethylene so jam some stuff underneath and only partially fill the "doughnut hole" from the top
and bottom.

My 400VA plitron is about 2 inches thick and the fill is about one inch thick

[SheldonD]

One other thing the toroid on getting warm will expand somewhat, 1 mm is not very much expansion space.

What will be the result on your chassis if it expands
more than that?

[troystg]

Hi-

I taped the hole on the bottom and while the torid was sitting flat filled it 3/4 of the way with rubber silicone caulk.

After it dried (long time due to it being a short thick plug) I put a bolt through it and a washer nut combo squeezing down on the silicone.

1. The silicone was dried to the torid so it was secure.

2. Squeezing down on the silicone put additional pressure on the inside of the torid further increasing the hold.


No metal inside the torid EXCEPT the bolt that was small in comparison to the core.

Similar in concept to the picture above but elastic and a little more forgiving if the bolt is not centered perfectly.


Good luck.