Transformer Alternative

[inf0]

Hey there

I don't have much experience with transformers so I wanted to ask if it would be possible to use a Carnhill VTB2281 in the place of a Lundahl LL5402 .
Both wired for 1:1 . The VTB2281 is ungapped , so that's another thing I don't know if is compatible ( is that the difference shown in the schematic with the center tap? )

I have a PCB that has the footprint of the Lundahls , is it as simple as wiring the equivalent pins to the board?
For example : Pin 1 of the VTB2281 to Pin 2 of the Lundhall footprint?

Thank you!

 

[Rusan]

Substituting transformers with equivalent specifications is generally okay, but substituting pin number for pin number is generally not. You are correct, you should ignore the pin numbers altogether and wire the VTB2281 according to your schematics, paying close attention to its phasing dots on pins 1, 4, 5 and 7, and match those to their correspondingly marked respective Lundahl pads 2, 4, 7 and 9 on your PCB. The pin numbering system used is irrelevant, but which end of each primary and secondary winding is connected in relation to its primary or secondary sister winding is of the utmost importance.

For example, connecting the VTB2281's primary windings in parallel requires that you connect pins 1 and 4, and pins 2 and 3. Series connection would require connecting pins 2 and 4. Do a quick online search for transformer winding phasing, which should turn up plenty of resources on the topic that can explain it far better than I can.

 

[inf0]

Substituting transformers with equivalent specifications is generally okay, but substituting pin number for pin number is generally not. In this case, you should ignore the pin numbers altogether. Wire the VTB2281 according to your schematics, paying close attention to its phasing dots on pins 1, 4, 5 and 7, and match those to their correspondingly marked respective Lundahl pads 2, 4, 7 and 9 on your PCB. The pin numbering system used is irrelevant, but which end of each primary and secondary winding is connected in relation to its primary or secondary sister winding is of the utmost importance.

Thank you! Any advice regarding the fact that VTB2281 is ungapped?

From my understanding , Pin 3 on the lundahl is shielding ? Which one would be the equivalent on the VTB2281?

 

[Rusan]

Thank you! Any advice regarding the fact that VTB2281 is ungapped?

Neither transformer is gapped. A gapped core is only necessary for applications where offset DC current is present in the primary winding.

From my understanding , Pin 3 on the lundahl is shielding ? Which one would be the equivalent on the VTB2281?

I presume the VTB2281 isn't enclosed in a can? I suppose you could connect the laminations to the pin 3 pad to act as a partial shield, perhaps by running a jumper lead from one of the trafo's mounting screws. Of course, doing this might also create a ground loop, if the transformer is bolted to a chassis that shares that same ground connection, so that's a consideration. If they have differing, floating ground references, inadvertently bridging them can be even much worse.

 

[inf0]

Neither transformer is gapped. A gapped core is only necessary for applications where offset DC current is present in the primary winding.



I presume the VTB2281 isn't enclosed in a can? I suppose you could connect the laminations to the pin 3 pad to act as a partial shield, perhaps by running a jumper lead from one of the trafo's mounting screws. Of course, doing this might also create a ground loop, if the transformer is bolted to a chassis that shares that same ground connection, so that's a consideration. Having differing, floating ground references and inadvertently bridging them can be even much worse.

Thank you, good to know ! Appreciate your help !

It will be bolted to the chassis so I guess I can try running a jumper cable and see if it creates a ground loop or not!