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New fuse for Astron 35?

Discussion in 'General Technical Questions and Answers' started by KM6LYW, Dec 21, 2018.

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  1. WA9SVD

    WA9SVD Ham Member QRZ Page


    Quite MY understanding. A 1 Ampere fuse @ 1 Ampere may well take minutes, or hours (or even longer) to "pop." @ 2 Amperes, maybe a few seconds. And I don't want to be around when a 32 Volt 10 Ampere fuse is used in (U.S.) standard 120+ Volts A.C. Much below 10 Amperes it MAY function OK, but much more than 10 amperes, (at any voltage above 32 Volts) look out! Shrapnel MAY result, but there CAN be an arc-over that keeps equipment powered long enough to cause irreparable damage.
    The MOST IMPORTANT thing to remember: "A fuse is meant to prevent a fire. " It is NOT meant to protect equipment. REPEAT AFTER ME>> It is NOT meant to protect equipment,:(just to prevent a fire.:rolleyes:
    Most solid state devices will die from over or reversed polarity long before a fuse can blow.:(
     
    KX4NJ and N0TZU like this.
  2. N0TZU

    N0TZU Platinum Subscriber Platinum Subscriber QRZ Page

    Yep. And consider their use in multimeters. For example, the fuses in a good quality UL and VDE listed multimeter such as a Fluke, compared to a cheap multimeter like the Harbor Freight giveaways.

    The Fluke fuse is huge and is rated to interrupt 10kA or something, and it will open to prevent the meter from exploding and catching fire in your hands if you accidentally short out, say, a 480VAC circuit. Whereas the HR is tiny and probably couldn’t interrupt a heated conversation! I wouldn’t want to be in the same room with one of those shorted across the mains.
     
  3. KA9JLM

    KA9JLM Ham Member QRZ Page

    Well that is a bit false.

    A fuse blows when a 12V radio is connected reverse polarity and the protection diode conducts.

    The fuse does protect from massive radio damage, Only if the proper fuse is used.

    And a fuse in a meter protects the meter from operator error. But it don't fix stupid. :rolleyes:
     
    Last edited: Jun 20, 2019
  4. W9KEY

    W9KEY XML Subscriber QRZ Page

    Just a minor clarification here - I believe a 1 Ampere fuse is rated to carry 1 amp continuously - and at "Rated" current should "never" open (at least at the manufacturer's rated temperature - usually 25 deg C).

    At any current above the "rated" current, the fuse will operate (trip) per the Time-Trip Curve shown on their Data Sheet.

    So in theory, a 1 Amp fuse should never blow at 1.0000 Amp, but should eventually blow at 1.0001 Amp. The key here is the TIME it takes - it could take many years/decades. In practice there are manufacturing tolerances associated with the element's resistance (remember it's I^2 * R that causes it to heat and open, and R is somewhat variable during manufacturing). So the Data Sheet omits defining that "No Mans Land", where actual operation is (practically speaking) not clearly shown. In other words, the Data Sheet is purposely not accurate enough to show the 1.0001 overload condition.

    Refer to this Littlefuse Data Sheet and observe the curve for the AGC 8 which started this long thread. Under magnification, you will note the 8A fuse model, even when running at 10 Amps may not trip in the 1000 second maximum time shown on the chart. It's implied (but not clearly defined) that "maybe" it will trip at some longer time - say perhaps 10,000 seconds - but you can't be sure since the chart is not detailed enough. But what is more clearly shown - at about 20 Amps (a 2x overload), it will trip in about 1 second.

    Anyway - my point is that an 8 Amp model fuse should carry 8 amps forever at rated ambient temperature.

    Another important point when applying fuses is "Let Thru Energy" which is time dependent (Watt-Seconds) and plays a major role in determining the damage done (or not done) downstream of the fuse during an overload condition. It's shown on the datasheet as I^2 * t (Current squared x Time) or Ampere squared Seconds. Think of it as the amount of energy that must be absorbed by your power supply wiring for the short time it takes the fuse to blow. The idea is to hopefully not start the wiring on fire (or exploding) before the fuse opens.
     
  5. WA9SVD

    WA9SVD Ham Member QRZ Page

    A properly rated fuse should blow quickly, to possibly protect equipment from damage, but is no insurance. If you use a 30 ampere rated fuse to "protect" a H-T that uses max 2 amperes, a "hefty" reverse polarity diode may well kill the H-T before the fuse blows.
     
  6. KA9JLM

    KA9JLM Ham Member QRZ Page

    Now that is funny. :)

    Is that in a vacuum ?
     
  7. K6BRN

    K6BRN XML Subscriber QRZ Page

    Heh! NOBODY here really understands fuzes! They blow up. That's what they do.

    Oh. Ok. NOT fireworks fuzes. "Fuses"?

    You mean those glass things in electrical boxes, the ones I usually pull out and replace with pennies? Gawsh! What DO they do? I know they don't prevent fires. They all burned up after I put my last penny in!

    I use the little round glass AGC250 type as spacers in my chairs. And when they crush, I know I'm too heavy! I have to start using bigger fuses for that. Too much glass on the floor.

    Wow! Eight pages on fuses for an Astron. I would have thought it would be simple. Who would have known the fuse is the ONLY thing that's not replaceable in an Astron RS-35. Learn something new and profound every day on these forums!

    Sorry - could NOT help myself. This thread is just TOO funny. Where's the beer? Next let's talk about "light bulbs" (incandescent/filament ONLY).

    Brian - K6BRN
     
  8. W9KEY

    W9KEY XML Subscriber QRZ Page

    Wow - I had to look that up ;).

    Per Google - a "light bulb" was an ancient device used by our ancestors (before LED's) - for example to illuminate the groves on their turntable's vinyl records.
    (For those unaware, "records" were pre-historic audio reproduction devices - commonly used during the last century).

    I believe amateur radios used an offshoot of the "light bulb" (called a valve or tube or something like that) primarily to warm their ham shacks, before the invention of central heating. Prone to high failure rates, "light bulbs" & "tubes" gave hams something to fix, when they weren't hamming.

    Thankfully, along with smallpox and the black plague, most of that old stuff is now long gone!
     
  9. W9WQA

    W9WQA Ham Member QRZ Page

    ha, all this nit picky detail. im not the least bit concerned about sticking in a 10 or 15 amp fuse,fb or slo blo in my astron.
    i have a 1 or 2 amp 3ag in a 3200 v power supply. yeah its a firecracker when it goes,glass is powder!
    too much worrying goin on here...
    in 65 yrs of melting good old 60/40 solder ive never caused a fire
     
  10. KF5LJW

    KF5LJW Ham Member QRZ Page

    False. Fuses are designed to operate at 80% capacity continuously.
     

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