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I am currently in the process of designing an automotive (motorsport related) fuse-box as a side project to my studies. I've not had much luck searching for fuse holders (20 position) however while searching I came across fuse holders for printed circuit boards. I'm wondering whether a PCB design would be out of the norm for a fuse-box?

The advantage I see is that I can have it custom to the size I'd ideally want. Though I'm not to sure whether the same PCB can be used to house the relays (micro). I'd like to have one PCB which houses the relays, fuses and regulators my existing design

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  • \$\begingroup\$ Normally you'd use panel mount fuse holders for this, which tend to have either solder lug or blade terminals on the back. \$\endgroup\$
    – pjc50
    May 15, 2015 at 13:50
  • \$\begingroup\$ @pjc50 would that mean I could then solder onto a board and that not affect the performance or reliability at all? \$\endgroup\$
    – Kristopher Rahim Afful-Brown
    May 15, 2015 at 13:55
  • \$\begingroup\$ No, you'd avoid a PCB entirely and use casework to hold the fuse holders in place and point-to-point wiring behind them. \$\endgroup\$
    – pjc50
    May 15, 2015 at 14:24

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The problem with PCBs in this application is two fold: 1) protecting the board from moisture (copper oxidises in the present of moisture) and 2) The current carrying capacity of the copper traces on the PCB. The copper layer on most PCBs is very thin and won't carry many amps of current. You could make the traces wider but almost certainly you'd have to either lay down copper wire on top of the traces and cover them in solder, or add a layer of solder onto the tracers all over to add thickness to enable the copper to carry the current.

Your best approach is to use fuse holders which have holes to mount them onto a flat surface and have screw fixings or solder tags for wires to be attached.

The moisture problem can be dealt with, using potting compound to keep out any moisture, but first off you need to deal with the problem of the copper layer on the PCB not being able to handle the current.

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  • \$\begingroup\$ So wither way, the need for a proper fuse holder is needed? And I yes, I can see PCB design being more problematic but foes it offer any advantages like weight and size compared to a normal fusebox design? \$\endgroup\$
    – Kristopher Rahim Afful-Brown
    May 15, 2015 at 11:31
  • \$\begingroup\$ I have seen fuse holders directly mounted on to PCBs, typically in consumer hi-fi amplifiers, the fuse is exposed. But these tend to be low current fuses, not 10A or 15Amps you'd find in a car. A PCB in a fusebox I can see only offers one advantage, mass production, using PCB manufacturing techniques and automatic placement of fuse holders and other connectors using pick-and-place machines. Wires have to be stripped and soldered which takes a human to do and takes time and therefore would be more costly than using a PCB. \$\endgroup\$
    – Dean
    May 15, 2015 at 13:37
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Maybe you should mention some more info on how you plan to use the relays. PCB mounted fuses are common so there is nothing exotic about them. Only thing I would miss when using PCB mounted fuse holders in this kind of application are blade terminals for easy connection of wires.

I would add some kind of screw terminal of some sorts. Like a ERNI Power bug, or similar:

enter image description here

As the PCB would be in a harsh environment you should use a dust and waterproof enclosure (but with at least some kind of draining hole). Use coating on the PCB to keep it clear of moisture. There are lots of PCB in cars so there is nothing unusual about using a PCB in this kind of applications.

Regarding the current carrying capacity of the PCB you could use a bit thicker copper than standard. 70um perhaps. You will probably need to route it with copper pours rather than traces, it depends on how your CAD program works.

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  • \$\begingroup\$ So this fusebox design is part practice and part formula sae. I have a current layout of a standard design using fuse and relay holders (though it's hard to find the required sizes online). We currently use micros relays for the fan, injection and ignition coils and something called hiside (not sure what that means as I only do ElecEng). Would using PCB relays be problematic? \$\endgroup\$
    – Kristopher Rahim Afful-Brown
    May 15, 2015 at 13:52
  • \$\begingroup\$ Without knowing exactly how you use the relays for the injection and ignition coil I would say that PCB relays are fine. But use some kind of socket on the PCB so you can replace the relays easily. \$\endgroup\$
    – Dejvid_no1
    May 15, 2015 at 13:58
  • \$\begingroup\$ Unfortunately, as it's my first year as part of the team, I am having more of an intro to the electronics (though as the only ElecEng member, they've got me redesigning quite a bit of the old design). At the moment there are connected to the ecu via the fusebox. The previous years did this so that the current wasn't too high for the ecu. \$\endgroup\$
    – Kristopher Rahim Afful-Brown
    May 15, 2015 at 14:13

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