What is the white paste inside flyback power supply?

[edaenrico]

Hi,

I'm repairing a power supply unit.

I removed the plastic case and then I found a copper shield which is in close contact with the transformer.

Between the transformer and the copper shield there is a "white paste"?

What is that?

Thanks,
Enrico Migliore

 

[esp1]

hi,
It is most likely 'heat sink compound' used to ensure a good thermal contact between the copper and transformer.

E

http://www.heatsink-guide.com/compound.htm

 

[edaenrico]

Hi,

thank you for your answer.

The paste I have is white and not silver.

Take a look here:

https://itresident.com/wp-content/uploads/2012/06/IMG_9381.jpg

Ciao,
Enrico Migliore

 

[esp1]

If the white paste is 'firm' and semi solid, it looks as it could be some sort of potting compound.
Potting compound is often used to fix and hold components in place, also to reduce the electro-mechanical 'buzz' from transformers.

Note: heat sink compound can also be white [ mine is ], it remains sticky for many years but can eventually dry out.

E

 

[mtwieg]

If it's rubbery and doesn't make a mess, then it's definitely some sort of potting, meant to reduce vibration or increase sock resistance (like the blob in the bottom left of the photo).

If it's greasy and makes a mess, then it's thermal compound.

The stuff on the transformer could be either or both. Many potting compounds are made to have good thermal conductivity.

 

[D.A.(Tony)Stewart]

This copper and conductive grease shunts the EMI and heat away from insulated coils inside to increase power dissipation. Air flow helps even more.

I usually monitor temp with a thermistor epoxied to transfo. to bias 3 terminal regulator to drive a fan.

 

[KlausST]

Hi,

thermal compound with metal is silver, thermal compound with ceramics is white.

If the electrical conductivity of metal may cause problem, then use ceramic compound. Usually the metal compound has better heat transfer performance..

Klaus

 

[betwixt]

From the impression in the top surface, and the amount of the stuff, I would say that is certainly potting compound and not for heat sinking. It does carry some heat of course but not particularly well. I would say it is more for mechanical stability, to cushion the parts if the PSU is dropped.

Brian.