[ARC5] [Milsurplus] HV Fuses: You Were Right, I Was Wrong.. more

[Peter Gottlieb]

I saw a spec sheet saying the 1 amp fuse wire has 510 feet on the spool.  Still, 
for the high cost of it (and then you have a 400 year supply), the copper wire 
solution is looking mighty nice.

Peter


On 6/15/2012 11:58 PM, Roy Morgan wrote:
> On Jun 15, 2012, at 8:42 AM, J. Forster wrote:
>
>> If it were me, I'd try and get some 'fuse wire'. I don't know if it is
>> still available.
>    From a later post, it does seem to be available, but pricey: though the
> price per roll did not say how much you get on a roll.
>
>> ...If you can't find fuse wire, consider fine magnet wire with the
>> appropriate fusing current.
> On that point, I find in my notes file on fuses the following:
>
>> fuses.txt
>>  From K1LKY
>>
>> From: "Dr. Barry L. Ornitz"<ornitz at tricon.net>
>> To: "Tom Rauch"<w8ji at contesting.com>; "Old Tube Radios"
>> <boatanchors at theporch.com>
>> Sent: Thursday, December 09, 2004 1:45 PM
>> Subject: Re: Which begs the question...
>>
>>> Tom, W8JI, had an excellent discussion on protecting tubes and
>>> high voltage power supplies under fault conditions.  In this he
>>> wrote:
>> Resistor content clipped out..
>>
>>> Tom also wrote:
>>>
>>>> I'm guilty of using thin enameled wire as a HV link fuse,
>>>> and I have on occasion used carbon resistors to locate an
>>>> unknown fault (like which tube is arcing?). But for reliable
>>>> protection in commercial or tell-the-world-to-do-it-this-way
>>>> articles a bit more sensible engineering would be better.
>>> I have done this too, using 32 gage and smaller wire.  Always
>>> working near chemists, I had ready access to glass tubing to
>>> run this inside.  One trick was to use the spring from a
>>> ballpoint pen to put the wire under tension.  Thus when the
>>> wire fused, the spring would quickly separate the two ends,
>>> resulting in less arcing and ionization.  Like Tom, I would not
>>> want to do this with a commercial product design for production.
>>>
>>> A good approximation for the fusing current for copper wire
>>> with the length much greater than the diameter is:
>>>
>>>          I = 10244 * d^1.5
>>>
>>> where:  I = fusing current in amps,
>>>          d = wire diameter in inches.
>>>
>>> So for 32 AWG wire, the diameter is 7.95 mils, and the fusing
>>> current is approximately 7 amps.
>>>
>>>          73,  Barry     WA4VZQ     ornitz at tricon.net
>> At:
>>   http://www.railcar.co.uk/mechanical/data/fuses.htm
>> we find that no. 42 plain annealed copper wire used as fuse wire is
>> rated at 1.5 amps, with a blowing current of 2.5 amps.  (these may
>> be BWG sizes!)
>>
>>    Rating  Blowing current  wire size
>> 1.5          2.5                   42
>> 3             5                      38
>> 5             8                      36
>
> Roy
>
> Roy Morgan
> k1lky at earthlink.net
> K1LKY Since 1958 - Keep 'em Glowing!
>
>
>
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