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fuse with resistor in it?

Discussion in 'Electronic Basics' started by tempus fugit, Nov 10, 2003.

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  1. tempus fugit

    tempus fugit Guest

    Hey all;

    I'm looking to replace a fuse in a piece of gear and it looks like a normal
    fuse (you know, an inch and a half or so long glass cylinder aboiut 1/4" in
    diameter) exept that there is a resistor in there. I've never seen this
    before - can I just replace it with a standard fuse? What is the resistor
    doing in there (limiting the AC current draw)?

  3. I have seen such fuses before. If I remember correctly, they are slow
    blow fuses. During prolonged moderate overcurrent, the fuse blows when
    the resistor gets hot enough to melt a solder joint to it. For very
    severe overcurrent the fuse blows from a wire melting or maybe the
    resistor blowing. Look for a current rating on the fuse and chances are
    you can use any old slow blow fuse of the same shape/dimensions and amp

    - Don Klipstein ()
  4. Luhan Monat

    Luhan Monat Guest


    Although I have never seen this before, I have seen low value, low
    power, resistors used as fuses. This sounds like such a thing put in a
    tidy fuse container.

    Since you want to replace it, I must assume that the resistor is no
    longer readable. If you can still see the color bands, it is not yet
    blown and your problem lies elsewhere.
  5. There should be a type and current rating stamped into the end caps,
    along the sides. This is probably a low current fuse, and they can be
    fairly expensive. and are two large
    fuse manufacturers. They have plenty of information on fuses on their
    websites, if you dig for it.
  6. I've seen those also. From memory, the resistor is a 51 ohm, and one
    end is pulled on by a spring, so it will separate when the solder
    melts. The fuse rating is something like 1/10 amp or 1/8 amp.

    These were fairly common years ago, when size was not at such a
    premium. But nowadays, everything has to shoehorn into a palm-sized
    case, so they use Picofuses, which are about the size of a 1/4 or 1/8
    watt resistor. And of course, since they're soldered in, replacing
    them is much more difficult. (for the average Joe anyway..)

    Or maybe that resistor was a 15 ohm. Depends on how one looks at it
    quickly.. I'll have to check and see if I have an old fuse like
    that laying around.

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  7. tempus fugit

    tempus fugit Guest

    The fuse is rated 3/16 A (?!?), and the resistor appears to be 900k (I can
    still kind of make out the colours - white, brown, yellow).


  8. Luhan Monat

    Luhan Monat Guest


    The 3/16 A looks probable, the 900k value is not. I would just replace
    with an approximate slow-blow fuse rated at 1/4 amp. Fuses are not
    super critical. Even the 'proper' value may not always work properly.
  9. Ross Mac

    Ross Mac Guest

  10. Ross Mac

    Ross Mac Guest

  11. You mean you've never used a zero ohm resistor? they are very useful
    for bypassing an unused attenuator on a surface mount PC board. BTW,
    they come in 5% and 1% versions ;-)
  12. tempus fugit

    tempus fugit Guest

    Thanks Luhan. That's kind of what I figured.
  13. Ross Mac

    Ross Mac Guest

    Not too many that looked like pico fuses!
    I do remember seeing zero ohm resistors or jumpers used on single sided
    boards. I think they did that so they could auto insert the part. A plain
    wire would not be so easy to auto insert!....take care Mike and where do you
    live in Central Florida? We were considering relocating to that area.....
  14. I live between Ocala and Belleview.
  15. Ross Mac

    Ross Mac Guest

    That's amazing because we were looking to move to the Ocala / Silver Springs
    area.....I won't ask if you like must!....Any
    suggestions???....thanks for the reply...Ross
  16. I've seen them used for configuration ties too. ...same reason
    wires aren't used, with the addition that they look like they're
    needed for operation (harder to circumvent the design).

    <snipped the yucky Florida stuff - though we had snow last night>
  17. The Ocala area is nice. You don't have the typical Florida sand all
    over, there are plenty of oak trees, and the town is a mix of old and
    new buildings. The roads are mostly decent, and slowly getting better.
    The only thing I don't like is that there is no electronics distributors
    between Orlando and Jacksonville, unless they are hiding from me.

    One think to be sure of: have a good title search on any property you
    want to buy, and if there is land involved, you might want to use a
    lawyer rather than a realtor to make sure everything is done right. If
    you are going to be in the area looking it over you can E-mail me and I
    will give you my phone number and address.

    I live in an older subdivision near Belleview, with the "Greenbelt"
    running right behind the property. It was originally to be used to build
    a canal across the state for NASA to bring things from the gulf to the
    cape, but it was never completed.

    BTW, the old "Tarzan" movies were filmed in Silver Springs.
  18. It was 39 degrees in Ocala this morning. Not quite cold enough to
    snow, but it felt great!
  19. Ross Mac

    Ross Mac Guest

    Thanks Mike, we will be looking this spring....have to sell a California
    house first!....thanks again, Ross
  20. That's getting down there for Florida in November. It was 23F
    this morning and 36F now at 3:20PM. That should be about the
    high, since the sun will be setting in about an hour. :-(
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