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

Sat Jun 16 09:46:14 EDT 2012

FYI McMaster Carr has two types of fuses rated 1000 vdc,  one is designed for commercial solar panel use - is somewhat expensive at $25 each and comes in several current ratings

The other type is intended for use in multimeters and is less expensive   Both types are spec-ed with the maximum interrupt current

I have not been following this thread close enough to remember the voltage in question but I suppose it would be in excess of 1000 vdc.  Still these fuses would work better than conventional fuses and two or three in series might well do the trick

________________________________
 From: Peter Gottlieb <nerd at verizon.net>
To: jfor at quikus.com 
Cc: arc5 at mailman.qth.net 
Sent: Saturday, June 16, 2012 9:38 AM
Subject: Re: [ARC5] [Milsurplus] HV Fuses:  You Were Right, I Was Wrong..  more

Yeah but you'll feel even worse if you spent $80 to protect that $500 tube and 
STILL had the $500 tube blow first!

No guarantee the "proper" fuse will perform any better.  I^2t calculations were 
rarely ever done back then, and even if they did, what could they do about it?  
Their choices were fast blow, normal, slow blow and no-blow (forego fuse) and 
for some components it made little difference, they were going down no matter what.

...P

On 6/16/2012 9:25 AM, J. Forster wrote:
> It might be worth the $80 if you are protecting a $500 tube!
>
> I remember an old comment about expensive devices blowing to protect the
> fuse....
>
>
> -John
>
> ==========
>
>> 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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