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Old 24th November 2010, 11:16 PM   #1
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Default Polyswitch fuse for speaker protection

Hi,
I want to protect the 1" HF horn ( 40W/8 Ohms ) of my bass guitar cabinet with a Polyswitch resettable fuse. If I have calculated well the result for my HF is 2.23A. Do I have to match this result with the trip current of the Polyswitch? The RXEF- 110 shows a 2.2A trip current : Digi-Key - RXEF110-ND (Manufacturer - RXEF110) .Is it the right one or do I have to choose another value ?: http://dkc3.digikey.com/PDF/US2010/P2107.pdf
Many thanks,
Pascalou
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Old 25th November 2010, 01:38 AM   #2
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Yes, that's what's given by the calculator at Loudspeaker Protection Components
Quote:
Input instruction (a guide line according to our experience):
For
- PA tweeters half the the rated power handling should be entered
lautsprechershop
Ref #110
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Old 25th November 2010, 02:06 AM   #3
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Thank you
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Old 27th November 2010, 07:43 AM   #4
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Default Be advised...

I used these in a couple builds, and it actually added an ohm of resistance to the design with it engaged and not preventing the current. You may need to lessen your L-pad a smidge.

Also- I would recommend placing a 12-15 ohm resistor in parallel with the Polyswitch so that you know the driver is okay when it interrupts the circuit. It will just strongly limit its output when engaged. After the polyswitch cools, the output will return to normal.

Later,
Wolf
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Old 27th November 2010, 05:13 PM   #5
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Wolf, can you - or anyone having experience too - please
say a word or two about "audibility" of polyswitches ?

Are there any effects before reaching the "trip current" ?

Is there any ageing noticeable, especially when switched
more often ?

Kind Regards
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Old 27th November 2010, 06:17 PM   #6
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Quote:
Originally Posted by LineArray View Post
Wolf, can you - or anyone having experience too - please
say a word or two about "audibility" of polyswitches ?

Are there any effects before reaching the "trip current" ?

Is there any ageing noticeable, especially when switched
more often ?

Kind Regards
I can't tell it's there, other than the reduced output. I have not tried it without on one of the 2 I've used them.

Don't know that either- I've never managed to trip one.

Later,
Wolf
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Old 28th November 2010, 12:27 PM   #7
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Thank you Wolf,

i found some information on characteristics
of PTC resetable fuses, unfortunately the
text is in german language only:

http://www.controllersandpcs.de/lehr...pass01_04x.pdf

The rise in resistance between "normal" and "tripped"
state seems to be highly frequency dependent.

Especially in the tripped state, there is a capacitive
component.

Nevertheless the elements seem to be usable quite
well for the purpose, see attached picture ...
Attached Images
File Type: jpg PTC_frequency_dependency.JPG (77.4 KB, 160 views)
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Last edited by LineArray; 28th November 2010 at 12:37 PM.
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