Fuse: Slow vs Fast blow | FerrariChat

Fuse: Slow vs Fast blow

Discussion in '308/328' started by Jonny Law, Mar 17, 2010.

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  1. Jonny Law

    Jonny Law F1 Rookie
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    Anyone have experience using the slow blow versus the fast blow fuses in the Birdman fuse blocks? Trying to decide which one to install or avoid.
     
  2. BigTex

    BigTex Seven Time F1 World Champ
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    Slow blow fuses are for special applications.

    You want standard fuses, which clear the fault as quickly as possible, in most circuits.
     
  3. Dr Tommy Cosgrove

    Dr Tommy Cosgrove Three Time F1 World Champ
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    I am not an expert but just from a common sense opinion - fast blow fuse. A blown fuse is an indication of a problem and you don't want that problem simmering upstream from that fuse. Let a regular fuse stop it immediately.
     
  4. Jonny Law

    Jonny Law F1 Rookie
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    Thanks guys. I did find this out. Don't know if the 308's have a spiking problem.

    Do not use a slow blow fuse in place of a fast acting fuse. It may not open fast enough to prevent components damage under a high current condition. It's not harmful to replace a slow blow fuse with a fast-acting fuse, but it will probably open up unnecessarily every now and then when the equipment is first switch on. A blown fuse can tell you something about your service problem. Often the glass case of the fuse appears clear, and you can still see the broken pieces of the fuse element. This means you have the kind of problem that causes a slow, gradual overload on the power supply. Some fuses even die of old age. But if the inside of the glass fuse is discolored, and there is no trace of the fuse element (the center connector), you know that the center connector was destroyed quickly and violently, using a lot of heat. The fault was a short circuit or other problem that caused a lot of current to flow very quickly.

    Is some cases a fuse will open up fast enough when there is a surge so that other components aren't damaged. If this is the case, replacing the fuse with one of the same type and rating restores operation. Unfortunately, a high probability exists that if a fuse blew, something in the circuit it was protecting shorted out. In this case, a replacement fuse blows right away. The blown fuse can easily be replaced by a new one, after the overload has been eliminated when come into replacement. Use only the same current and voltage ratings as the original. The common type and current rating of a fuse in a monitor are slow blow 2A to 5A. When you buy replacement fuses, get several - you can easily use all of them while you're troubleshooting an elusive problem.
     
  5. Paul_308

    Paul_308 Formula 3

    Mar 12, 2004
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    I use resettable circuit breakers in my windows circuit. Since I turbo'ed the windows they do have high current spikes occasionally. However my fuse blocks are not Birdman but made for newer ATO fuses for which plugin breakers are commonly available.

    Which circuits are you concerned with changing to slo-blo protection?

    ________________________
    http://www.FerrariWiring.com
     
  6. Jonny Law

    Jonny Law F1 Rookie
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    Not specifically any. Found 8A slow last night and just with in the last hour 7A fast. Just trying to determine if I need to keep hunting.
     
  7. Jedi

    Jedi Moderator
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    Slow-blow fuses are for applications where momentary current surges are expected and
    are tolerable. VERY uncommon these days - they date from the tube era, where
    startup current of circuits could be higher than "normal acquiescent load" - the slow-blow fuse
    could withstand the momentary excess current of charging electrolytic capacitors in
    the power supply. There are a few other special applications, but they are few.

    Fast-blow fuses blow at the instant their load-carrying specification is exceeded.

    For cars, fast-blow only. Period. Unless it's for the tube radio in a 1940's or 50's
    car, and only if the power wiring is sufficient to handle the exceeded load for a second
    or two.

    Jedi
     
  8. Jonny Law

    Jonny Law F1 Rookie
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    Thanks guys. Was able to find some 7.5 A fast blow at Baxters last night.
     

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