PTC resistors for protection of small transformers

roffe · 24th October 2007, 11:51 AM

I am looking at certain transformers from Hahn (examples: http://www.hahn-trafo.com/english/ei38.php ), and notice this:

"Primary protection by means of transformer hegt coils to IEC 127 standards or secondarily with PTC resistances".

I must admit that I am pretty new to PTC resistances.

Can someone who knows explain a bit on how to select the correct PTC resistor and implement transformer protection for a specific transformer (schematics or by explanation)?

MaKari · 14th November 2007, 09:19 AM

Please, check the link: http://edn.com/archives/1996/011896/02df5.htm

Anyway the primary fuse is the must in diy equipment.

fernando_g · 15th November 2007, 01:03 PM

I agree with MaKari. A primary fuse is mandatory protection.

The problem that I see with PTCs is that their trip point varies substantially with ambient temperature. Therefore, they should be seen as backup protection only, the fuse is always a must.

24th October 2007, 11:51 AM	#1
roffe diyAudio Member Join Date: Oct 2005	PTC resistors for protection of small transformers I am looking at certain transformers from Hahn (examples: http://www.hahn-trafo.com/english/ei38.php ), and notice this: "Primary protection by means of transformer hegt coils to IEC 127 standards or secondarily with PTC resistances". I must admit that I am pretty new to PTC resistances. Can someone who knows explain a bit on how to select the correct PTC resistor and implement transformer protection for a specific transformer (schematics or by explanation)?

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14th November 2007, 09:19 AM	#2
MaKari diyAudio Member Join Date: Apr 2007	Please, check the link: http://edn.com/archives/1996/011896/02df5.htm Anyway the primary fuse is the must in diy equipment.

15th November 2007, 01:03 PM	#3
fernando_g diyAudio Member Join Date: Nov 2007	I agree with MaKari. A primary fuse is mandatory protection. The problem that I see with PTCs is that their trip point varies substantially with ambient temperature. Therefore, they should be seen as backup protection only, the fuse is always a must.