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PTC resistors for protection of small transformers
PTC resistors for protection of small transformers
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Old 24th October 2007, 11:51 AM   #1
roffe is offline roffe  Norway
diyAudio Member
Join Date: Oct 2005
Default 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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Old 14th November 2007, 09:19 AM   #2
MaKari is offline MaKari  Finland
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.
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Old 15th November 2007, 01:03 PM   #3
fernando_g is offline fernando_g  United States
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.
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