About my Thoroid transformer...

[JW1977]

The plastic tape that covers the transformer, is it only there to protect the Windings?
Ive seen hifi transformers laying in a plastic "cup" and it was my intention to make one of these in my 3D printer and put the transformer in it.

Why then? The Cables needed som work so i had to take the plastictape off.

Is there any good reason that i shouldnt?

[john swift]

why did you need to work on the transformer ?

if you only wanted longer wires then I would of spliced extension wiring to the transformer

if you removed some turns from a winding to lower the output voltage
then I would replace the original tape with new heat resistant tape
eg
glass cloth electrical tape with thermosetting poly acrylate adhesive/ heat class F

Any 3D printed support needs to withstand the temperature the transformer runs at

your probably looking at a 3D plastic part that needs to be safe at 130 to 150 C
and not prevent the natural cooling of the transformer

John

[JW1977]

The rubbercoat of the wires was falling off so to fix this I had to take the tape off.
I just did a little research and found out that I could just buy one of these cups, they are made of metal.
I thought that if i put the cover on i dont have to rewind the protection tape.

[john swift]

OK , that makes sense renewing the old insulation
I would still replace the tape

Is this Mounting Disc the type of thing your looking out ?
https://uk.rs-online.com/web/p/mounting-kits/6719208/

using a Neoprene Disc
https://uk.rs-online.com/web/p/mounting-kits/6719211/

helps to even out the pressure on the transformer

just watch out you don't accidently form a shorted turn by
connecting the top metal mounting disk to the bottom disk or chassis

John

[Voicecoil]

Reasons toroids are potted in a plastic case include reducing audible hum (potting compound locks the windings solid) and because they may look smarter! - important for HiFi. To do it properly you need a vacuum potting chamber to drive the resin inbetween the turns of wire. If the primary winding is on the outside you'll need some kind of insulation when potting in a metal can to preserve the breakdown specification - better to have the secondary on the outside in such designs.

[JW1977]

Yes, i think im gonna go with that and skip the cover...
Sometime i read about how not to mount one of these transformers but i dont remeber now.
Would this be a bad way? The top metal disc would be connected to the cabinetchassis if i do it like this.
26392

[JW1977]

Thanks for the info, i decide to go with the tape instead! :smile:

[JW1977]

Sorry i forgot to Reply with quote... :shame:

[john swift]

yes, the diagram in post 6 is the usual way to mount an open toroidal transformer

if its fitted in a low profile metal enclosure just make sure the lid can not touch the bolt head and form a shorted turn !

John

[JW1977]

yes, the diagram in post 6 is the usual way to mount an open toroidal transformer

if its fitted in a low profile metal enclosure just make sure it can not touch the bolt and form a shorted turn !

John

Feeling stupid now but, make sure what cant touch the bolt?
The chassis would be in contact with the screw by mounting it in it or am i missing something?

[john swift]

Any connection between the bolt head and the chassis will result in a shorted turn

but if its fitted in a low profile metal enclosure
then it may be possible for the top to be deformed and touch the bolt head if pressure is applied !

26393

John

[JW1977]

Any connection between the bolt head and the chassis will result in a shorted turn

but if its fitted in a low profile metal enclosure
then it may be possible for the top to be deformed and touch the bolt head if pressure is applied !

26393

John

How about the lower end? The nut will be in contact there right?

[john swift]

the lower end is OK as the chassis , bolt and top mounting disk don't form a complete turn around the toroidal core

its only when you close the loop by connecting the mounting disk to the chassis by a conductor outside the core

John

[JW1977]

the lower end is OK as the chassis , bolt and top mounting disk don't form a complete turn around the toroidal core

its only when you close the loop by connecting the mounting disk to the chassis by a conductor outside the core

John

Allright, thanks! :thumsup:
When were at it, what type of fuses would you use for a PSU?

[Voicecoil]

Allright, thanks! :thumsup:
When were at it, what type of fuses would you use for a PSU?

For a toroidal transformer feeding a rectifier/smoothing capacitors you'll need a time delay (T) fuse as the switch on current surge can be VERY large.

However if you have a fairly constant power drain you can reduce the surge by fitting a NTC thermistor in series

[john swift]

Any idea what the transformers VA rating is ?

As a toroidal transformer inrush current is very large
I would not be supprised if you need a fuse 3 or 4 times what the VA rating would indicate

if you have a 600VA transformer
you may have to use a HRC 10A mains fuse (HRC = High Rupture Capacity)

and check what type of circuit breaker is supplying the radial circuit your mains socket connected to

for example
a type B breaker trips at 3 to 5 times the full load current operating time 0.04 To 13 Sec

a type C breaker trips at 5 to 10 times the full load current operating time 0.04 To 5 Sec

John

PS

if the transformer is large enough you may have to consider using an inrush current limiter
some examples here -
https://sound-au.com/articles/inrush.htm

PPS
more details of a Soft-Start Circuit
https://sound-au.com/project39.htm

[JW1977]

For a toroidal transformer feeding a rectifier/smoothing capacitors you'll need a time delay (T) fuse as the switch on current surge can be VERY large.

However if you have a fairly constant power drain you can reduce the surge by fitting a NTC thermistor in series
Allright, i have to keep looking into that...

[JW1977]

Any idea what the transformers VA rating is ?

As a toroidal transformer inrush current is very large
I would not be supprised if you need a fuse 3 or 4 times what the VA rating would indicate

if you have a 600VA transformer
you may have to use a HRC 10A mains fuse (HRC = High Rupture Capacity)

and check what type of circuit breaker is supplying the radial circuit your mains socket connected to

for example
a type B breaker trips at 3 to 5 times the full load current operating time 0.04 To 13 Sec

a type C breaker trips at 5 to 10 times the full load current operating time 0.04 To 5 Sec

John

PS

if the transformer is large enough you may have to consider using an inrush current limiter
some examples here -
https://sound-au.com/articles/inrush.htm

PPS
more details of a Soft-Start Circuit
https://sound-au.com/project39.htm
Yes, its 800VA. Got some Reading to do about this, thanks!