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Fuses problem

:: EPE Chat Zone ­:: ­Radio Bygones Message Board :: » EPE Forum Archives 2007-2009 » Archive through 05 July, 2008 » Fuses problem « Previous Next »

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bruce
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Username: bruce

Post Number: 38
Registered: 04-2008

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Posted on Saturday, 21 June, 2008 - 01:52 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

hi all,
I have come across a type of fuse recently that I've not seen before and I wondered if anyone knew more about them.
They're often found on motherboards, and they look rather like a ceramic capacitor.One I have here is thin, flat ( square) and plastic-coated. And it's bright yellow. The markings are 'X30' and 'U160'
I cant tell if this is a wire fuse, a solid state
ic device or a thermal device. Or what the rating is.
Anybody know?
Bruce
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joe
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Username: joe

Post Number: 434
Registered: 05-2005

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Posted on Saturday, 21 June, 2008 - 01:59 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Bruce,

How do you know it's a fuse ?

Joe
Do one thing each day that scares you – work here !
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bruce
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Username: bruce

Post Number: 40
Registered: 04-2008

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Posted on Saturday, 21 June, 2008 - 02:43 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Because the symbol on the board underneath is a fuse symbol and they are numbered F1, F2.....
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gordon
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Post Number: 441
Registered: 05-2005

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Posted on Saturday, 21 June, 2008 - 05:03 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

They sound like resettable polyfuses, some info. here.

http://en.wikipedia.org/wiki/Resettable_fuse

Not sure what the markings mean, but for USB port protection the value might be 500mA.
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stylers
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Username: stylers

Post Number: 110
Registered: 04-2005

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Posted on Sunday, 22 June, 2008 - 01:14 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

resettable polyfuses as gordon said, also known as "polyfuses". fuses of suspect reliability in my experience..
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vlf
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Username: vlf

Post Number: 161
Registered: 10-2005


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Posted on Sunday, 22 June, 2008 - 01:27 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Um... I use these a lot in development projects, there OK if you work out the RMS current being used for the applied job, and give head-room for the thermal cut-out which is usually x 2 to the series current.

Regards, Brian.
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bruce
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Username: bruce

Post Number: 42
Registered: 04-2008

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Posted on Sunday, 22 June, 2008 - 06:27 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

They sound perfect for the kind of stuff I do.
In fact, I've just come across a motherboard with some, but instead of being marked F1, F2 etc, they are marked 'Th', a symbol you see used for thermistors. So it looks like they are polyfuses, which ARE thermistors.
So far so good. Now the tricky bit - how do you deciper the code? Eg what does 'X30 U160' mean?
Bruce
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vlf
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Username: vlf

Post Number: 162
Registered: 10-2005


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Posted on Monday, 23 June, 2008 - 12:09 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Bruce, these markings I have not encounted; the ones I have used actually state there ratings current, .1A and so-on... like this range from Rapid:

http://www.rapidonline.com/Electrical-Power/Fuses-Circuit-Breakers/Resettable-Fuses

The ones you have might be from large production manufacturing, where type numbers are used rather than individual ratings being stated.

Regards, Brian.
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bruce
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Username: bruce

Post Number: 44
Registered: 04-2008

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Posted on Monday, 23 June, 2008 - 08:41 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Thanks Brian
In fact, they're so cheap it may not be worth messing about. Although.... as they're thermistors and resettable, one could just push, say, 3X the max expected current through them and see if they trip
Bruce
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vlf
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Username: vlf

Post Number: 163
Registered: 10-2005


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Posted on Monday, 23 June, 2008 - 11:25 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Hi Bruce, they do trip close to the stated rating about twice there series handling current, being thermal resistance the drop is sharp, and thus voltage is dissapated into heat.

Regards, Brian.

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