Welding the transformer core laminations...

[Externet]

Hi.
What is the purpose of the weld lines ? What differs if not welded or grinding them out ? (Image is from a microwave oven transformer )

 

[ZipZapOuch]

Transformer laminations are often welded together primarily to reduce noise and vibration, particularly in transformers used in applications like microwave ovens. Welding the laminations, which are thin sheets of steel, helps to create a more solid structure, minimizing movement and the resulting humming or buzzing sounds caused by the fluctuating magnetic field.


Here's a more detailed explanation:

• Minimizing Vibration: Transformer cores are made of stacked layers of thin, electrically insulated steel sheets called laminations. When an alternating current flows through the transformer's windings, it creates a fluctuating magnetic field that can cause these laminations to vibrate, producing noise. Welding the laminations together, especially in the "E" and "I" core configurations common in microwave transformers, helps to dampen these vibrations and reduce the noise.
• Acoustic Noise Reduction: The welding process, along with other methods like resin coating, helps to create a more rigid core structure, minimizing the movement and vibration of the laminations that leads to acoustic noise.
• Cost-Effective Assembly: In some transformer designs, welding is used as a cost-effective method for assembling the core, particularly in mass-produced transformers like those used in microwave ovens. While insulation is crucial for preventing eddy current losses, welding can be a more efficient way to hold the laminations together than other methods like using bolts and brackets.
• Eddy Current Considerations: While welding can create a path for eddy currents, in some applications the reduction in vibration and noise outweighs the increase in eddy current losses. In power transformers, insulation between laminations is more critical, and welding is generally avoided in favor of other methods to maintain high efficiency.

 

[MaxHeadRoom78]

Another method I have used after grinding off the weld in order to remove the laminations when adding or modifying the core windings, is to dip or coat it in winding shellac afterwards, as is done with motor stators, etc.
BTW, if reusing a M-Wave transformer, remember to punch out the magnetic shunt they usually possess.

 

[ahsrabrifat]

Hi.
What is the purpose of the weld lines ? What differs if not welded or grinding them out ? (Image is from a microwave oven transformer )

View attachment 150426

A welded core can help ensure that the magnetic flux generated by the transformer’s primary coil is contained effectively within the core material. The structure of the core influences the efficiency of the transformer, and welds help maintain its integrity and performance.

 

[MaxHeadRoom78]

The downside is any welds partially defeat the heating effect reduced by using laminations, intending to overcome this.
I have never personally experienced any negative effects after reassembling any TFMR I have made a mod to.!?

 

[ZipZapOuch]

I have never personally experienced any negative effects after reassembling any TFMR I have made a mod to.!?

Even if you would have, they would have turned positive in about 8.3mSec.

 

[Externet]

Hi.
Am in the process of dismantling two identical microwave oven transformers by grinding weld strips to swap coils to make one transformer with two 120V coils and another transformer with two 2KV coils to yield two isolation transformers with no other purpose.
Which one needs the removal of the magnetic shunts ? The 2KV, the 120V , both or none ?

And what behavior will be different for each ? Both cases fed by 120VAC mains.

 

[MaxHeadRoom78]

Both can be removed for most applications.
Basically they limit the secondary current's capability.
Often the use for these TFMR;s is SMAW welding, where they should definitely be removed.