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Fixing a broken toroid


random.path
 

I dropped a toroid I was going to use for an antenna matchbox transformer, and it broke in two. I've super-glued it back together, and can only see the faintest hairline crack with a magnifier. My guess is that since we are dealing with fields and not electron flow within the toroid that it will still perform as well as it would have before the accident.

What say an expert?

Thanks,
Chip
AE5KA


John DeJournett
 

I was once told that in Ham Radio and antennas in particular, anything works, but some work better than others.  I would say try it.  For an experiment you are out nothing but your time.  If the performance isn't up to expectations though, you will want to replace the core.


On Wed, Mar 6, 2013 at 9:35 AM, CStratton <groups@...> wrote:
 

I dropped a toroid I was going to use for an antenna matchbox transformer, and it broke in two. I've super-glued it back together, and can only see the faintest hairline crack with a magnifier. My guess is that since we are dealing with fields and not electron flow within the toroid that it will still perform as well as it would have before the accident.

What say an expert?

Thanks,
Chip
AE5KA



nm0s_qrp <ai9e_qrp@...>
 

In my experience, if it is an iron powder toroid, the effect of gluing a broken part will be minimal. There will be some minor drift of its value over time as oxygen and humidity enter at the break, but if the toroid is part of an output filter network, it is not a major problem. If it is part of a VFO, you might want to consider replacing it.

If the part is a ferrite, there will be a more significant change in its inductance from the small gap that is introduced in the magnetic circuit, especially if the part is a high permeability material like 72 or 77. For an RF transformer, where the open circuit inductance is not critical, you are probably OK. If it is part of a tuned circuit (where ferrites are seldom used), check the circuit to see how a change of inductance will affect it.

73 NM0S

--- In 4sqrp@..., CStratton <groups@...> wrote:

I dropped a toroid I was going to use for an antenna matchbox transformer,
and it broke in two. I've super-glued it back together, and can only see
the faintest hairline crack with a magnifier. My guess is that since we are
dealing with fields and not electron flow within the toroid that it will
still perform as well as it would have before the accident.

What say an expert?

Thanks,
Chip
AE5KA


Todd K7TFC
 

I, too, have heard of the changes (AsubL?) introduced by gaps in toroids. Instead of glue, I think I might be inclined to use either tape or a zip tie around the circumference of the toroid to hold it back together. I think the right-sized zip tie would be easier because it would allow for more-careful adjustment of the two halves (by cinching the tie to the point of snuggness) before cinching it up tight.  

Now I'm sure there would be changes in the number of windings required since the wire would also be wound over the zip tie. It might be, though, that the way to do that would be to use tape to hold the two halves together while winding the toroid, but then to cinch it up tight afterwards with a tie.

73,

Todd
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On Wed, Mar 6, 2013 at 7:56 AM, nm0s_qrp <ai9e_qrp@...> wrote:
 

In my experience, if it is an iron powder toroid, the effect of gluing a broken part will be minimal. There will be some minor drift of its value over time as oxygen and humidity enter at the break, but if the toroid is part of an output filter network, it is not a major problem. If it is part of a VFO, you might want to consider replacing it.

If the part is a ferrite, there will be a more significant change in its inductance from the small gap that is introduced in the magnetic circuit, especially if the part is a high permeability material like 72 or 77. For an RF transformer, where the open circuit inductance is not critical, you are probably OK. If it is part of a tuned circuit (where ferrites are seldom used), check the circuit to see how a change of inductance will affect it.

73 NM0S



--- In 4sqrp@..., CStratton wrote:
>
> I dropped a toroid I was going to use for an antenna matchbox transformer,
> and it broke in two. I've super-glued it back together, and can only see
> the faintest hairline crack with a magnifier. My guess is that since we are
> dealing with fields and not electron flow within the toroid that it will
> still perform as well as it would have before the accident.
>
> What say an expert?
>
> Thanks,
> Chip
> AE5KA
>