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Question about 16V POLYFUSER Radial Leaded Resettable PTC Av

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jskiba(at)icosa.net
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Posted: Sun Jan 03, 2010 7:42 pm Post subject: Question about 16V POLYFUSER Radial Leaded Resettable PTC Av

I just noticed these at digikey web site as a new product….  

   

Looks like one could use these instead of fuses or the traditional circuit breakers (for the average range of protection)  

   

But my question is do these trip the same as typical fuses ? I know they can reset but would it work like a fuse for time to trip or protection of the wire ?  

   

Catalog page:  

http://media.digikey.com/pdf/New%20Cat%20Page/101/Littelfuse/Polyfuse%20PTC%20Reset%20Devices.pdf  

   

   

Here is a link to the Data sheet  

   

http://www.littelfuse.com/data/en/Data_Sheets/Littelfuse_PTC_16R.pdf  

   

it looks like they are used in a max volts of 16v (good, my system runs at 13.8 volts)  

   

and they have ones that range from: 2.5a to 14a  

   



 Price looks cheap  

   

Light weight   

   

Small in size   

   

Other thoughts – comments – concerns ?  

   

Thanks  

   

Jeff  

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etienne.phillips(at)gmail
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Posted: Mon Jan 04, 2010 11:49 am Post subject: Question about 16V POLYFUSER Radial Leaded Resettable PTC Av

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.

However, as has been mentioned by a fellow respondent,  if your downstream device is something like an EFIS, or a device with an intelligent power supply that turns off when the supply voltage drops below a threshold, the polyswitch will probably reset itself, as the current draw that it sees goes to 0A and it cools down. To fix this, you need to add a dummy load with enough current flowing through it to keep the polyswitch tripped until you cycle the power to it manually.

As soon as you start adding in this functionality, you need to start weighing up the added complexity of many failure-prone components, on one failure-prone fiberglass sheet, with micron-thick failure-prone copper tracking, against a couple robust tefzel wires crimped and bolted onto a robust CB... As an electrical engineer (yes, I've been following the Engineers in the real-world discussion!) and I'm a fan of blinking lights and push buttons when it affords me the opportunity to get some experience designing something more complex than a matchbox. However I fly VFR by day only and have complete steam backup and a handheld radio, so if I lose all electrics, it has no impact on my ability to complete the flight safely and with no discomfort. 

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 

Thanks

Etienne



On 04 Jan 2010, at 5:41 AM, Jeffrey W. Skiba wrote:

[quote]I just noticed these at digikey web site as a new product….

 

Looks like one could use these instead of fuses or the traditional circuit breakers (for the average range of protection)

 

But my question is do these trip the same as typical fuses ? I know they can reset but would it work like a fuse for time to trip or protection of the wire ?

 

Catalog page:

http://media.digikey.com/pdf/New%20Cat%20Page/101/Littelfuse/Polyfuse%20PTC%20Reset%20Devices.pdf

 

 

Here is a link to the Data sheet

 

http://www.littelfuse.com/data/en/Data_Sheets/Littelfuse_PTC_16R.pdf

 

it looks like they are used in a max volts of 16v (good, my system runs at 13.8 volts)

 

and they have ones that range from: 2.5a to 14a

 



Price looks cheap

 

Light weight

 

Small in size

 

Other thoughts – comments – concerns ?

 

Thanks

 

Jeff



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