Resetable Fuses

Discussion in 'General Electronics Chat' started by RodneyB, Mar 16, 2016.

  1. RodneyB

    Thread Starter Active Member

    Apr 28, 2012
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    I am trying to fit a reset-able fuse to protect a Charger I have fitted into a car. I think I was having a problem with a "Load Dump" destroying the circuit so I fitted an MOV across the supply.

    The whole circuit draws 2 Amps at peak current draw. However when using a blade type Auto fuse I had to fit a 15 Amp fuse otherwise it just blew.

    I want to protect my charger but at the same time dont want to be changing fuses all the time or having to do repairs because of the load dump.

    I have attached the drawing of my proposed circuit I am looking for some advice so as to be able to make sure I have everything covered.

    In the Load Dump i read on line about excess voltage and current in Alternators causing damage. I am assuming this is the problem.
     
  2. bwilliams60

    Active Member

    Nov 18, 2012
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    Fuses are made to blow instantly unless you use slow acting fuses. Try a circuit breaker instead. They are made to withstand current surges. Go to Littlefuse website for more info on size etc.
     
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  3. crutschow

    Expert

    Mar 14, 2008
    13,011
    3,233
    Load dump only occurs if the battery is suddenly disconnected when the alternator is charging so I doubt that's your problem.
    Try a slow-blow fuse.
     
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  4. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    :confused: Clearly the peak current was much greater than 2A. Have you considered an inrush-limiter NTC varistor?
     
  5. RodneyB

    Thread Starter Active Member

    Apr 28, 2012
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    I haven't, I am very interested. Anything to help this work better. Could you point me in a direction to do some reading
     
  6. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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  7. dl324

    Distinguished Member

    Mar 30, 2015
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  8. RodneyB

    Thread Starter Active Member

    Apr 28, 2012
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    Both of these directions to information is very informative. I now understand how a NTC works in theory, now the big challenge is to put it into practical use,

    I have looked at the datasheet of several and see they have an Imax at 25 degrees. My question is how do I select the correct NTC when my temperature ranges between 25 and 35 degrees. My full load current is 2 Amps.

    Is there any additional circuit required to putting the NTC in series to the load
     
  9. dl324

    Distinguished Member

    Mar 30, 2015
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    I use an Ametherm SL10 10004 and it doesn't specify any derating other than max current at 65C or less:
    upload_2016-3-17_8-39-59.png
    Generally the thermistor is sufficient unless the resistance at the nominal current is too high. Then you use the same technique that would be used for a simple resistor limiter; switch it out after the inrush event.
     
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