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Question about 16V POLYFUSER Radial Leaded Resettable PTC

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nuckolls.bob(at)aeroelect
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Posted: Tue Jan 05, 2010 7:09 am Post subject: Question about 16V POLYFUSER Radial Leaded Resettable PTC

At 11:16 AM 1/4/2010, you wrote:

Hi Jeff



I designed and have been using an electrical system similar to the 

EXP bus for over a year, for no reason other than experimentation. I 

chose a variety of these, ranging from 1A up to 16A... They work as 

advertised, and have found their trip performance similar to that of 

CB's, i.e. a 2A polyswitch probably won't trip at 2A, unless the 

device draws 2A for minutes almost. 2.5A will trip after a few 

seconds, 5A will trip after a second, and 100A will trip almost 

instantaneously.

  <snip>

So to answer your questions, yes I think they can replace CB's or 

standard fuses, but I don't think they should. The fact that they 

reset themselves whenever power is cycled means that a tripped system 

will not stay tripped if you turn off the master switch. Standard 

fuses are much better-suited to the task. And that's in my humble opinion



     Great observation.



     Bob . . .

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nuckolls.bob(at)aeroelect
Guest

Posted: Tue Jan 05, 2010 7:12 am Post subject: Question about 16V POLYFUSER Radial Leaded Resettable PTC

At 08:28 PM 1/4/2010, you wrote:

 	  Quote: 	
		  



See AC 43.13, chapter 11 quoted below:



11-50. RESETTABLE CIRCUIT PROTECTION

DEVICES.

a. All resettable type circuit breakers

must open the circuit irrespective of the position

of the operating control when an overload

or circuit fault exists. Such circuit breakers are

referred to as “trip free.”

b. Automatic reset circuit breakers, that

automatically reset themselves periodically, are

not recommended as circuit protection devices

for aircraft.


	


   This paragraph has been in there for decades . . .

   LONG before things like the polyfuse came along.

   The self-resetting breakers of yesteryear were

   simple adaptations of manual resetting breakers.

   Many cars used self-resetting breakers on headlight

   circuits in lieu of fuses.



   These devices would ALWAYS reset when they cooled.

   Unlike the polyfuse which will probably stay tripped

   until power is removed, the self-resetting breaker

   of 1950 would definitely oscillate between a zero-

   current to fault-current condition as long as power

   was still on.



   Bob . . .

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marcausman

Joined: 08 Feb 2007
Posts: 70

Posted: Tue Jan 05, 2010 7:21 pm Post subject: Re: Question about 16V POLYFUSER Radial Leaded Resettable

"Probably" ?

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_________________
Marc Ausman
http://www.verticalpower.com "Move up to a modern electrical system"
RV-7 IO-390 Flying

al38kit

Joined: 13 Jul 2009
Posts: 21

Posted: Tue Jan 05, 2010 8:23 pm Post subject: Re: Question about 16V POLYFUSER Radial Leaded Resettable

I have an EXP bus that I have been considering for my project.  (That I got for a $40, delivered.)  It looks like a slick unit.



I can understand the concern for a circuit resetting itself after the power is restored...but isn't that a reason we put switches on things?...Like leave that circuit off if it has a problem...



Sorry, just don't see the design as having much of a downside.  If you think you may accidentally turn the thing back on, put some red tape on the switch or something...pull the wire.



Al

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nuckolls.bob(at)aeroelect
Guest

Posted: Wed Jan 06, 2010 9:41 am Post subject: Question about 16V POLYFUSER Radial Leaded Resettable PTC

At 10:23 PM 1/5/2010, you wrote:

 	  Quote: 	
		  



I have an EXP bus that I have been considering for my 

project.  (That I got for a $40, delivered.)  It looks like a slick unit



Sorry, just don't see the design as having much of a downside.  If 

you think you may accidentally turn the thing back on, put some red 

tape on the switch or something...pull the wire.


	


   Have you read the discussions on this topic?

   Goto http://aeroelectric.com and do a a site

   search on . . .



   exp bus



   Keep in mind that a polyswitch MUST be powered to

   STAY tripped. Fault current is reduced to a "safe"

   level thus keeping it hot after a trip.



   Bob . . .

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