by "Trevor Wilson" <trevor@[EMAIL PROTECTED]
>
Apr 28, 2008 at 10:15 AM
"Phil Allison" <philallison@[EMAIL PROTECTED]
> wrote in message
news:67kgbfF2p1nigU1@[EMAIL PROTECTED]
>
> "Trevor Wilson"
>
>>>I wonder what the DC resistance of a 250mA fuse might
>>> be?
>>
>> **Depends on the fuse. I just measured half a dozen 0.25 Amp 3AG fuses.
>> They ranged from 12 Ohms up to 15 Ohms. COLD.
>
>
> ** That is an unbelievably high resistance value - not at all
> consistent with a 250mA fuse.
**Nevertheless, it is correct. I zero'd out the test lead resistance. I
double checked the figures with my handy dandy Bob Parker ESR meter. The
results were within acceptable limits.
>
> Some no brand, 1/4 amp 3AG fuses I checked ranged from 3.5 to 4.5 ohms.
>
> These 20mm "T" or delay fuses from Bussman are speced at 0.66 ohms for a
> 250mA size:
>
> http://www.farnell.com/datasheets/81115.pdf
>
> The specs show that R rises to 1 ohm at rated current.
**I checked the resistance rise of a 12 Ohm measured fuse. At 200ma, it
rose
to 15 Ohms. I probably over-stated the reality when I said: "several
times".
When I get some time, I'll take my measurements at levels closer to the
fuse
ratings. Based on what I found, I'd guess that the resistance of the fuse
will almost double at it's rated blow current (500ma).
>
>
>
>> ** Fuses act as non-linear resistors. They get hot and change
resistance.
>
>
> ** Speaker voice coils do that too.
**They do indeed.
Trevor Wilson
