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How to choose and where to get proper electronic fuses

Discussion in 'General Electronics Discussion' started by Hellmut1956, Apr 30, 2016.

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  1. Hellmut1956


    Aug 11, 2014
    Hi, I am building a Panel for my electronic lab and I want to protect it from possible short circuits:


    This first picture shows a front view. The different voltages coming from a modified PC 600 W power supply are fed hidden to the lower row of receptacle connectors, then fed to the switch and the upper row gives access to the supply depending on the switch position.


    Here a view to the same panel from below. It shows the cables that come from the connector row on the right edge of the picture. Below the panel you see the screwable connectors, 5 for each tension, so that I as the user have the choice to select if I want to use the receptacle connector on the front side of the panel or connect a cable to one of the related screwable connectors.


    here you see why I came to the conclusion a short circuit protection is necessary! Let's take a detailed look at the white cable connecting the power to the corresponding screwable connectors. The risk that a short circuit could happen any time in the future does not only result from short circuits taking place further down the line, but also i.e. the white and the green cable are so close to each other that a short is possible! Of course I will install not conducting physical barriers to prevent this from happening, but I also want to place electronic fused just before the connectors row on the right edge show in a picture above.

    Now that you have the background info for my question, here my questions:

    I want to use electronic self resetting fuses, PTC's, that cut the line if a sudden rise of the current flowing to the increases. How can I find the proper PTC fuses?

    Here the data for maximum allowed currents for the lines providing the tensions to the Panel:

    -12 VDC: 6A
    -5 VDC: 6A
    +3.3 VDC: 10A
    + 5 VDC: 10 A
    +12 VDC: 6A
    +24 VDC: 10A
    +24 VDC to 40 VDC: 10 A

    The first 5 tensions come directly from the PC power supply, the 24 VDC up to 10 A are the result of a tension doubling circuit and the last supply comes from a battery pack of 12 LiFePO4 connected in series and where the tensions does fluctuate between this values depending of how much this pack supplies from Full to empty for recharge!

    I do not want to use melting fuses as shorts may happen quite a few times and I want the fuses to react relatively fast!
  2. dorke


    Jun 20, 2015
    1. PPTCs are not very fast, they are as fast as slow-blow fuses.
    2. You can get them from TE ,little-fuse, and others.
    3. If you use a banana biding post like this one you can eliminate the need for the terminal blocks.
    4. Your build should be very well insulated and use proper thickness wires.
  3. hevans1944

    hevans1944 Hop - AC8NS

    Jun 21, 2012
    At the currents you are anticipating, along with the probability of accidental shorts while experimenting, I would recommend using a panel-mounted reset-able thermal-mechanical circuit breaker such as found on this Google page result.

    PTCs are good for non-frequent "trips" but don't provide any indication that something has gone wrong except for loss of power. And after they cool off they come on again, which may not be immediately desirable. Years ago (in the previous century) I built a power supply using a through-hole panel-mounted aircraft circuit breaker. This was the pop-out variety rather than a toggle switch. It not only provided positive indication when tripped, but could also be used as a disconnect switch by pulling on the pop-out indicator.

    Unfortunately, back then they were very expensive so I could only afford to use one, placed in the mains circuit. Today, they are much less expensive and well worth it for the convenience they provide in a bench power supply. They are also available in a rocker actuator style that could directly replace your existing power switches.
  4. Hellmut1956


    Aug 11, 2014
    Thx a lot for your answers. I am getting the impression that as long as the max. voltage is high enough only the amount of current should be used to select a proper electronic fuse. For the 6 A requirements I have to select a fuse type that has its hold value at 6A and a trip value, assumed to be twice the value of the hold value, taken from the video would be a trip value of 12 A. This fuse would be the same for all tensions I have set the 6 A requirement. Accordingly for the 10A requirement 1o A/20 A? Is this correct?
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