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Polyfuses

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user9253

Joined: 28 Mar 2008
Posts: 1921
Location: Riley TWP Michigan

Posted: Sun Mar 01, 2009 7:23 am Post subject: Polyfuses

On page 50 of the April 2009 issue of Kitplanes Magazine, Bob Fritz installs Polyfuses in his Jabiru.  He said that Polyfuses are used to protect electric window motors in cars.  Have Polyfuses been proven in the field to be reliable?  If so, can we or should we be using them in our airplanes?  The endurance bus would be an ideal application for Polyfuses.  They would protect the wiring by limiting the current.  If they open, they will automatically reset upon removal of the overload condition.  Bob Fritz put LEDs in parallel with the Polyfuses to indicate an overload condition.  Advantages of the Polyfuse are light weight, low cost, do not take up panel space, and require no pilot action to reset.  What do you think?

Joe

_________________
Joe Gores

Dale Ensing

Joined: 11 Jan 2006
Posts: 571
Location: Aero Plantation Weddington NC

Posted: Sun Mar 01, 2009 8:15 am Post subject: Polyfuses

The EXP BUS uses polyfuses. The unit is my RV-6A has been problem 

free/working successfully for five years.

Dale Ensing



---

_________________
Dale Ensing
RV-6A
Aero Plantation
Weddington NC

nuckolls.bob(at)aeroelect
Guest

Posted: Sun Mar 01, 2009 12:57 pm Post subject: Polyfuses

At 10:13 AM 3/1/2009, you wrote:

[quote]

<densing(at)carolina.rr.com>



The EXP BUS uses polyfuses. The unit is my RV-6A has been problem 

free/working successfully for five years.

Dale Ensing



---

peter(at)sportingaero.com
Guest

Posted: Sun Mar 01, 2009 3:03 pm Post subject: Polyfuses

My EXPBUS had been problem free for 7 years but is now giving occasional

very short duration (momentary) power cuts. Really tricky to figure exactly

what is going on. I thinking of ripping it out and installing a regular fuse

block. Will also be much easier to add electrical items in the future.



Peter

RV-6A ~600 hours



--

marcausman

Joined: 08 Feb 2007
Posts: 70

Posted: Thu Mar 05, 2009 12:12 pm Post subject: Re: Polyfuses

Technically there's nothing wrong with polyfuses. But I am not a fan of using them in an aviation application because you cannot control them directly like you can an electronic (solid state) circuit breaker or old-style circuit breaker. At least when a fuse blows the circuit stays off.

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

nuckolls.bob(at)aeroelect
Guest

Posted: Thu Mar 05, 2009 12:46 pm Post subject: Polyfuses

At 02:12 PM 3/5/2009, you wrote:

 	  Quote: 	
		  



Technically there's nothing wrong with polyfuses. But I am not a fan 

of using them in an aviation application because you cannot control 

them directly like you can an electronic (solid state) circuit 

breaker or old-style circuit breaker. At least when a fuse blows the 

circuit stays off.


	


    Sure. We (the TC guys) never had an arugment

    with the ability of the polyfuse to perform

    as advertised. Our problem was delivering to

    traditional design goals of which you mentioned

    two, control and non-self re-setting. The other

    problem was that the parts are not bolt-in, wire

    up and play. You have to install them on some

    manufactured assembly that incorporates an

    etched circuit board for mounting the parts.

    Even if we popped for the custom assembly, the

    TOTAL cost of acquisition/ownership wasn't

    that much better than what we were already

    doing. The breaker as a mil-qualified bolt-in-

    and-play parts require no special attention

    to mix and match as needed. A customized assembly

    has to be designed, qualified and becomes very

    hard to change once approved for the airframe.

        Bob . . .



        ----------------------------------------)

        ( . . .  a long habit of not thinking   )

        ( a thing wrong, gives it a superficial )

        ( appearance of being right . . .       )

        (                                       )

        (                  -Thomas Paine 1776-  )

        ----------------------------------------

msausen

Joined: 25 Oct 2007
Posts: 559
Location: Appleton, WI USA

Posted: Mon Mar 09, 2009 7:35 pm Post subject: Polyfuses

So here's a thought then for a potentially suitable application for these little monsters where there is some $value$.  Ignoring the fact that these are surface mount creatures and a suitable and robust mounting mechanism would be needed, what about a scenario where you have a rear mounted battery and need to protect a wire in which a fuse would not be useable.  Say if a device has a low power requirement but for some reason has a crowbar circuit in it like maybe a Lightspeed ignition.  



  Like I said before, I'm not keen on using a relay as that is nothing more than a workaround in my mind and introduces a whole new failure mode plus a bunch of additional wiring.  The self resetting nature of the Polyfuse wouldn't be a big deal as I would still want a master switch on each LSE.  Checklist item would be the best solution to addressing when to reset a "blown" ignition.  More importantly it would allow the crowbarred (is that a word) ignition to be reset without the need to access a inaccessible fuse/breaker or use a relay to shoe horn a breaker into an accessible location.



  So can someone tell me why this would not work to address the recent revelations around LSE's?  I still would rather use a fuse or breaker but it seems to be as good or better than some of the other alternatives (big wire, relay).



--

nuckolls.bob(at)aeroelect
Guest

Posted: Wed Mar 11, 2009 7:15 pm Post subject: Polyfuses

At 10:30 PM 3/9/2009, you wrote:

 	  Quote: 	
		  

Sausen)" <rvbuilder(at)sausen.net>



   So here's a thought then for a potentially suitable application 

 for these little monsters where there is some $value$.  Ignoring 

 the fact that these are surface mount creatures and a suitable and 

 robust mounting mechanism would be needed, what about a scenario 

 where you have a rear mounted battery and need to protect a wire in 

 which a fuse would not be useable.  Say if a device has a low power 

 requirement but for some reason has a crowbar circuit in it like 

 maybe a Lightspeed ignition.  



   Like I said before, I'm not keen on using a relay as that is 

 nothing more than a workaround in my mind and introduces a whole 

 new failure mode plus a bunch of additional wiring.  The self 

 resetting nature of the Polyfuse wouldn't be a big deal as I would 

 still want a master switch on each LSE.  Checklist item would be 

 the best solution to addressing when to reset a "blown" 

 ignition.  More importantly it would allow the crowbarred (is that 

 a word) ignition to be reset without the need to access a 

 inaccessible fuse/breaker or use a relay to shoe horn a breaker 

 into an accessible location.



   So can someone tell me why this would not work to address the 

 recent revelations around LSE's?  I still would rather use a fuse 

 or breaker but it seems to be as good or better than some of the 

 other alternatives (big wire, relay).


	


         I think I'm lost. How would the polyfuse facilitate

         an alternative to big wires and/or relays? I don't

         recall a conversation about relays except for heavy

         duty alternate feed paths for the e-bus.



         I'm not seeing your point about a polyfuse being

         more attractive than a fuse or breaker in the

         same slot. Can you enlighten me?



        Bob . . .



        ----------------------------------------)

        ( . . .  a long habit of not thinking   )

        ( a thing wrong, gives it a superficial )

        ( appearance of being right . . .       )

        (                                       )

        (                  -Thomas Paine 1776-  )

        ----------------------------------------

msausen

Joined: 25 Oct 2007
Posts: 559
Location: Appleton, WI USA

Posted: Thu Mar 12, 2009 5:00 am Post subject: Polyfuses

Let me see if I can refresh your memory.  Because of the undocumented crowbar "feature" in the LSE ignitions that came to light recently, you had suggested using a relay to provide power to an unprotected wire in the case of a rear mounted battery.



  The concern was that the LSE could cause a trip/blow in an OV situation however the ignition would be fine and require a reset.  In a rear mounted battery the only way to accommodate this need to reset was to put a breaker up on the panel but this left an unprotected line from the battery to the CB.  You suggested a standard relay would be the best way to address this and I didn't like the additional complexity in addition to replacing one potential failure mode with another.  



  It seems to me that a Polyfuse would address the need to reset a nuisance trip and allow the protection to stay back by the battery without needing to add relays (more wires, additional failure points, and additional switches) or big fuses/fat wires to get a CB up within arm's reach.



Michael



--

nuckolls.bob(at)aeroelect
Guest

Posted: Thu Mar 12, 2009 4:12 pm Post subject: Polyfuses

At 07:56 AM 3/12/2009, you wrote:

 	  Quote: 	
		  

Sausen)" <rvbuilder(at)sausen.net>



   Let me see if I can refresh your memory.  Because of the 

 undocumented crowbar "feature" in the LSE ignitions that came to 

 light recently, you had suggested using a relay to provide power to 

 an unprotected wire in the case of a rear mounted battery.


	


   Is the crowbar feature for real? Somebody else mentioned that

   they thought this was a mis-understanding of some variety.

   You LSE customers should be curious/concerned about this . . .

   which one is going to call/write LSE and find out?

 	  Quote: 	
		     The concern was that the LSE could cause a trip/blow in an OV 

 situation however the ignition would be fine and require a 

 reset.  In a rear mounted battery the only way to accommodate this 

 need to reset was to put a breaker up on the panel but this left an 

 unprotected line from the battery to the CB.  You suggested a 

 standard relay would be the best way to address this and I didn't 

 like the additional complexity in addition to replacing one 

 potential failure mode with another.


	


 	  Quote: 	
		     It seems to me that a Polyfuse would address the need to reset a 

 nuisance trip and allow the protection to stay back by the battery 

 without needing to add relays (more wires, additional failure 

 points, and additional switches) or big fuses/fat wires to get a CB 

 up within arm's reach.


	


   Okay, I remember.  Yeah, the polyfuse looks attractive

   for this. You might even consider a switch-breaker for

   the panel mounted control . . . or even just a switch.

   The wire-protection issue is covered with the polyfuse.

   Now . . . about that robust mounting. Let me think about

   this a bit. We could use the same technique for the

   NTC inrush limiters too. They have the same mounting

   challenge.



   I've got to place an order with Digikey tomorrow for

   some project parts. I'll get both NTC and PTC devices

   coming and see if we can figure out a way to make these

   things suitable for the aircraft installation.



   Bob . . .

msausen

Joined: 25 Oct 2007
Posts: 559
Location: Appleton, WI USA

Posted: Thu Mar 12, 2009 5:05 pm Post subject: Polyfuses

The source of the information got it directly from Klaus so I think we can at least assume it's correct for this exercise.  I agree on the switch at the panel.  I probably won't have a key switch so my intention is to use a normal switch for power control.  Thanks for looking into this, let us know if you come up with anything on the mounting.



Michael



--

nuckolls.bob(at)aeroelect
Guest

Posted: Fri Mar 13, 2009 7:11 am Post subject: Polyfuses

At 07:56 PM 3/12/2009, you wrote:

 	  Quote: 	
		  

Sausen)" <rvbuilder(at)sausen.net>



   The source of the information got it directly from Klaus so I 

 think we can at least assume it's correct for this exercise.  I 

 agree on the switch at the panel.  I probably won't have a key 

 switch so my intention is to use a normal switch for power 

 control.  Thanks for looking into this, let us know if you come up 

 with anything on the mounting.



Michael


	


   Okay. Can't do better than that. Let's explore the polyfuse thing

   closer. Maybe we can find a "real" use for these puppies

   after all . . .

        Bob . . .



        ----------------------------------------)

        ( . . .  a long habit of not thinking   )

        ( a thing wrong, gives it a superficial )

        ( appearance of being right . . .       )

        (                                       )

        (                  -Thomas Paine 1776-  )

        ----------------------------------------

fvalarm(at)rapidnet.net
Guest

Posted: Fri Mar 13, 2009 9:19 am Post subject: Polyfuses

When "trying to think of a good situation to use polyfuses" I don't know for

sure but seem to recall that once tripped they will not reset until the

TOTAL load is removed (switched off) presumably to let the polyfuse cool

down.  Can anyone confirm this?  If this is true, it is important to

consider when designing an application.  You don't want to automatically

lose another powered device because of a fault in another (same as with a

breaker supplying power to more than one device).  Nor do you want another

non-switchable load, or another load which is not known, on the same

polyfuse.  This would make it impossible to eliminate the complete load on

the polyfuse, preventing it from being reset. Am I wrong?



I have never used polyfuses but the above is based on what I have read here

and on other lists.  I still prefer a single traditional breaker (requires

manual reset) or fuse (requires manual replacement) for EACH load on the

airplane. Considering also, that they are easy to integrate into an airframe

and maintain, what's wrong with traditional circuit protection?



Bevan

retasker(at)optonline.net
Guest

Posted: Fri Mar 13, 2009 10:12 am Post subject: Polyfuses

You are correct in your description.  Nothing wrong with either fuses or 

breakers, but the individual in question has a somewhat unique situation 

for which a polyfuse would provide a possibly better solution.  I 

believe he plans to use a separate polyfuse for each load in question.



Dick



B Tomm wrote:

 	  Quote: 	
		   



  

 When "trying to think of a good situation to use polyfuses" I don't know for

 sure but seem to recall that once tripped they will not reset until the

 TOTAL load is removed (switched off) presumably to let the polyfuse cool

 down.  Can anyone confirm this?  If this is true, it is important to

 consider when designing an application.  You don't want to automatically

 lose another powered device because of a fault in another (same as with a

 breaker supplying power to more than one device).  Nor do you want another

 non-switchable load, or another load which is not known, on the same

 polyfuse.  This would make it impossible to eliminate the complete load on

 the polyfuse, preventing it from being reset. Am I wrong?



 I have never used polyfuses but the above is based on what I have read here

 and on other lists.  I still prefer a single traditional breaker (requires

 manual reset) or fuse (requires manual replacement) for EACH load on the

 airplane. Considering also, that they are easy to integrate into an airframe

 and maintain, what's wrong with traditional circuit protection?



 Bevan

nuckolls.bob(at)aeroelect
Guest

Posted: Fri Mar 13, 2009 1:05 pm Post subject: Polyfuses

At 12:13 PM 3/13/2009, you wrote:

 	  Quote: 	
		  

When "trying to think of a good situation to use polyfuses" I don't know for

sure but seem to recall that once tripped they will not reset until the

TOTAL load is removed (switched off) presumably to let the polyfuse cool

down.  Can anyone confirm this?


	


   Correct. The devices I've ordered for a first pass look will

   go into a "tripped" state at about 150 mA of continuous current

   or about 2 watts of internal heat being dissipated.

 	  Quote: 	
		  If this is true, it is important to

consider when designing an application.  You don't want to automatically

lose another powered device because of a fault in another (same as with a

breaker supplying power to more than one device).  Nor do you want another

non-switchable load, or another load which is not known, on the same

polyfuse.  This would make it impossible to eliminate the complete load on

the polyfuse, preventing it from being reset. Am I wrong?


	


   You are correct. As shown in the proposed system integration drawings, one

   and only one system tied to the protection module and it needs

   some means by which the circuit can be broken (switch). Of course,

   you would want a switch on any ignition system anyhow.



 	  Quote: 	
		  I have never used polyfuses but the above is based on what I have read here

and on other lists.  I still prefer a single traditional breaker (requires

manual reset) or fuse (requires manual replacement) for EACH load on the

airplane. Considering also, that they are easy to integrate into an airframe

and maintain, what's wrong with traditional circuit protection?


	


   Nothing. In this case, we're interested in feeding from an

   always-hot source (battery bus) to favor an electrically

   dependent engine. Always-hot feeders like to be protected

   as close the source as practical. Hence some manner of

   remotely mounted circuit breaker is attractive - ESPECIALLY

   if your battery is back in the tail. Here we discover a

   unique set of design goals that look with more favor

   upon the much misunderstood and oft misapplied polyfuse.



   It's even more attractive given that I have some standard

   product enclosures . . .



http://aeroelectric.com/Pictures/Products/A09_Package.jpg



   . . . that reduce the cost of getting these little critters

   boxed up and bolted to the airplane.



   I'm getting private email from folks wanting to order

   this thing which is gratifying but premature. Let's

   make sure we have done a good thing first. After sifting

   the sands of design for polyfuses for over 20 years,

   it WOULD be pretty cool to find a place where they

   smoothly fit into a cost effective and well considered

   design aboard an aircraft.





        Bob . . .



        ----------------------------------------)

        ( . . .  a long habit of not thinking   )

        ( a thing wrong, gives it a superficial )

        ( appearance of being right . . .       )

        (                                       )

        (                  -Thomas Paine 1776-  )

        ----------------------------------------

nuckolls.bob(at)aeroelect
Guest

Posted: Sun Mar 15, 2009 9:37 am Post subject: Polyfuses

At 04:03 PM 3/13/2009, you wrote:



    <snip>



 	  Quote: 	
		     It's even more attractive given that I have some standard

   product enclosures . . .



http://aeroelectric.com/Pictures/Products/A09_Package.jpg



   . . . that reduce the cost of getting these little critters

   boxed up and bolted to the airplane.


	




   After pondering this project for a few days, I've

   distilled the magnitude of the effort down considerably.

   The "magic" parts we're adapting to our design goals

   are really inexpensive. It just doesn't make sense

   to wrap a lot of materials and labor costs around

   their utilization. I've got some ideas for a do-it-

   yerself packaging scheme. I still need to do some

   temperature testing in the chamber to make sure we

   don't have thermal performance issues with either

   operation of the polyfuse or failure of the packaging

   technique.



   Bottom line is that if the present idea works, these

   will be really easy to use for the purposes identified

   in earlier postings to this thread.



        Bob . . .



        ----------------------------------------)

        ( . . .  a long habit of not thinking   )

        ( a thing wrong, gives it a superficial )

        ( appearance of being right . . .       )

        (                                       )

        (                  -Thomas Paine 1776-  )

        ----------------------------------------

bcondrey

Joined: 03 Apr 2006
Posts: 580

Posted: Sun Mar 15, 2009 10:00 am Post subject: Re: Polyfuses

I reported this "feature" on this forum although there might also have been others.  I got the information directly from Klaus at LSE via a telephone call.  Another individual that I personally know called Klaus to advise him of this thread and behavior was confirmed to him. 



I think the polyfuse approach is a great solution and look forward to Bob N's testing.  Assuming that all turns out well I'll be ordering also.



Bob

RV-10 N442PM (flying)



>Is the crowbar feature for real? Somebody else mentioned that 

> they thought this was a mis-understanding of some variety. 

> You LSE customers should be curious/concerned about this . . . 

> which one is going to call/write LSE and find out?

Radioflyer

Joined: 04 Feb 2009
Posts: 43
Location: Boston

Posted: Mon Mar 16, 2009 6:37 am Post subject: Re: Polyfuses

I'm late into this discussion, but have been wondering how to implement the polyfuses since I first read about them in Jim Weir's article and Blue Mountain's wiring guide. They are very attractive to me due to their compact size, inexpensiveness, and solid state reliability. Everyone agrees they perform as advertised. But, as others have stated, the packaging issue makes their use somewhat problematic, especially if you're interested in taking them offline, bypassing their auto-reset feature.



What I would like to see is a polyfuse mounted into an ATC fuse shell, preferably one of those ATC types that have the LED already built in to indicate a fault. By so doing, you could use the readily available ATC fuse blocks, thereby retaining the option to simply pull the Polyfuse out when you need to. For my first attempt, I was going to try a little surgery on an ATC fuse package and epoxy a Polyfuse to it..., but I have not yet taken the chance to play with this. My guess is that it may be only a matter of time before some Taiwanese manufacturer starts putting polyfuses in the ATC fuse format.



--Jose

longg(at)pjm.com
Guest

Posted: Mon Mar 16, 2009 8:03 am Post subject: Polyfuses

Jose,



Would you bet your life on a floppy adaptation on your Lightspeed

ignition? Perhaps yours is just cursory interest. I'm sure you can jam

pennies in there if you like. There's no reason that would not work.



Right now I am using Bob's proposed schematic which adds two in-line 30

amp fuses in front of two 5 amp breakers. He also considered two relays

in place of the 30 amp ATC's. 



I guess my deal is how am I going to get at those 30 amp in-line fuses

and still keep my eye on flying the airplane. I suppose if you blow two

30 amp fuses behind the two five amp breakers suggested by LSA, you're

already in deep doo-doo. 



I wanted to ask Bob why the 30 amp fuse? Couldn't we get-a-way with

something lighter, say 20 amp?



Glenn

--

nuckolls.bob(at)aeroelect
Guest

Posted: Tue Mar 17, 2009 6:13 pm Post subject: Polyfuses

At 11:01 AM 3/16/2009, you wrote:

 	  Quote: 	
		  



Jose,



Would you bet your life on a floppy adaptation on your Lightspeed

ignition? Perhaps yours is just cursory interest. I'm sure you can jam

pennies in there if you like. There's no reason that would not work.



Right now I am using Bob's proposed schematic which adds two in-line 30

amp fuses in front of two 5 amp breakers. He also considered two relays

in place of the 30 amp ATC's.



I guess my deal is how am I going to get at those 30 amp in-line fuses

and still keep my eye on flying the airplane. I suppose if you blow two

30 amp fuses behind the two five amp breakers suggested by LSA, you're

already in deep doo-doo.



I wanted to ask Bob why the 30 amp fuse? Couldn't we get-a-way with

something lighter, say 20 amp?


	


   No . . . well . . . depends. When you compare the various

   time-to-trip curves for over-current protection, there's

   a often overlooked consideration - response time.



   Magnetic breakers and electronic breakers can be exceedingly

   fast. Most thermal devices are tailored to a design goal.

   For example, you can get 5A fast blow fuses and 5A slow blow

   fuses. Thermal breakers as a class of circuit protector

   are generally VERY slow compared to a fuse of the same ratings.

   So, hook a 5A breaker in series with a 5A fuse and hit

   the feeder with a short. The fuse opens every time. Keep

   increasing the fuse size and you'll find that it probably

   takes a 20A fuse to out-muscle a 5A breaker. So for good

   headroom in the design, we make the upstream protection MUCH

   more robust than the downstream protection.



   This is why ANL limiters are exceedingly robust. They are

   intended to be part of a distribution system wherein

   no single downstream feeder protection can trip an

   upstream feeder protection . . . even if the upstream

   feeder is running say 100% of system average. See:



http://aeroelectric.com/Mfgr_Data/Fuses_and_Current_Limiters/Bussman/ANL_Specs.pdf



   Note that the "rating" for a current limiter

   includes enough headroom that it can be loaded to

   100% of rating and still stand off a downstream

   breaker or fuse trip.



   I'm working and accident right now wherein redundant

   feeders to a common bus were protected with fuses

   and not current limiters with an unfortunate outcome.



   This is IMPORTANT. This is why my 5A crowbar breaker

   feed is protected upstream with a fusible link.

   The breaker will always open before the fusible link.



   Bob . . .



 	  Quote: 	
		  What I would like to see is a polyfuse mounted into an ATC fuse shell,

preferably one of those ATC types that have the LED already built in to

indicate a fault. By so doing, you could use the readily available ATC

fuse blocks, thereby retaining the option to simply pull the Polyfuse

out when you need to. For my first attempt, I was going to try a little

surgery on an ATC fuse package and epoxy a Polyfuse to it..., but I have

not yet taken the chance to play with this. My guess is that it may be

only a matter of time before some Taiwanese manufacturer starts putting

polyfuses in the ATC fuse format.


	


   Read the discussions on my website about the downside for

   having self resetting circuit protection. The Polyfuse is

   not a drop-in replacement for fuses or breakers. The

   design task I'm working right now goes to a very specific

   application of the Polyfuse. Similarly, fusible links

   are not to be used in place of breakers or fuses without

   sifting all the simple ideas and making sure design

   goals are being met.



   Polyfuses ARE used in automobiles. Seat adjuster motors

   and widow riser motors are commonly protected with Polyfuses.

   But you can be sure that if there were good value in

   using them everywhere, the car guys would have ditched

   the fuse block a long time ago. They ARE NOT directly

   interchangeable technologies.



   Bob . . .

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