Hello.

A switching power supply (110/220) smoldered one of its parts, either a varistor or a thermistor and I'm looking for a replacement.

The symbol for RT1 looks like a varistor. However, the component is connected in series to Line Neutral with no other path from Neutral to the rest of the board. This would suggest the component is a thermistor, according to my reading.

Could anyone comment?

Also, for this 600W/12V power supply (even though the board reads 500W ... WTH!?) with a switching input 110/220V, what is a proper replacement value?

Thanks.

 

Welcome to AAC!
It's probably an inrush current limiter.

 

Welcome to AAC!
It's probably an inrush current limiter.

Thanks for the info.

With the output of (purportedly) 50A at 12V, and input of 110V, would I be looking for a thermistor with a max. steady state current of 6A (assuming some loss in the power supply, 600W input at 110V is 5.5A). Is this the correct way to think about this?

 

Hello.

A switching power supply (110/220) smoldered one of its parts, either a varistor or a thermistor and I'm looking for a replacement.

The symbol for RT1 looks like a varistor. However, the component is connected in series to Line Neutral with no other path from Neutral to the rest of the board. This would suggest the component is a thermistor, according to my reading.

Could anyone comment?

Also, for this 600W/12V power supply (even though the board reads 500W ... WTH!?) with a switching input 110/220V, what is a proper replacement value?

Thanks.

The symbol on the PCB does seem to be for a Varistor Clamp. YMMV as the OP might be correct as it really being a current limiter (but normally with NA power the limiter is on the 'HOT' side connection after the power switch and fuse for safety reasons).
Connection diagram examples.




https://www.mouser.com/new/bourns/bournsMOV/
https://www.mouser.com/pdfDocs/bour...he-right-mov-surge-suppressor-white-paper.pdf

 

Found a very related posting: "Trying to identify a blown thermistor"

https://forum.allaboutcircuits.com/threads/trying-to-identify-a-blown-thermistor.177455/

Also on a low-cost transformer, also a thermistor on the neutral line.

The post also has links to videos on a blown 50A transformer, likely a very similar design to mine. And the conclusion is: probably not trying to fix.