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  1. #1
    Join Date
    Apr 2013
    Location
    Nantwich, Cheshire
    Posts
    418

    Default What's going on with this fuse box!????

    Hi folks,
    I put one of these (admittedly in the camper) but I have one on the boat as well....https://www.ebay.co.uk/itm/12V-24V-1...gAAOSwEEVdS6g1

    Tracking down a failed water pump I find there is only 10.3V at the feed to the pump. Eventually I discovered that on the above fuse box half of the outputs are at 10.3V. Not just on one side, randomly across the lot. The feed to the fuse box is good 12.4V and the ground is good. What am I missing here, seems to defy the laws of physics!
    Most of the 10.3v outputs aren't connected, without fuses, but some are, which included the pump, which I've now piggy backed onto a light circuit - pump now works. I'd like to understand what's happening, or is it just a duff unit. Can't say I tested it - the pump has been working for a year without any problems. I think the other connected outputs are feeding led lights so probably a bit dim, but I haven't tracked back the feeds to work out which ones.
    Cutlass 27

  2. #2
    Join Date
    Sep 2010
    Location
    Alness / Black Isle Northern Scottish Highlands.
    Posts
    9,238

    Default Re: What's going on with this fuse box!????

    I would say duff unit, poor connection from input terminal to one bank of fuses. There is a lot of nice looking stuff for sale that is at it's heart, a load of carp.

  3. #3
    Join Date
    Jul 2003
    Location
    West Australia
    Posts
    11,668

    Default Re: What's going on with this fuse box!????

    The volt drop is caused by current flow through a resistance. So look for what is running at the time of the test. Then look for what components are in series with this current flow. ie switch fuse or wiring. The connections showing the lower volts ie the drop then are sharing this current path. There is no other logical possibility unless there are diodes sneaked in there.
    Put your positive volt meter lead on the positive input to the fuse box. ie where volts are good. Now put the negative lead onto the output of your various devices to measure the volt drop. You won't get any volt drop unless something is operating. Or unless resistance is very high. The fuse box may have a master high current fuse which may be high resistance. Don't forget to check out the negative side of the current path.
    ol'will
    Last edited by William_H; 18-09-19 at 00:16.

  4. #4
    Join Date
    May 2016
    Location
    Suffolk
    Posts
    8,025

    Default Re: What's going on with this fuse box!????

    Quote Originally Posted by MarcJ View Post
    Most of the 10.3v outputs aren't connected, without fuses
    Quote Originally Posted by William_H View Post
    The volt drop is caused by current flow through a resistance. So look for what is running at the time of the test.
    Rainbow Marine.
    www.rainbowmarine.co.uk

  5. #5
    Join Date
    May 2016
    Location
    Suffolk
    Posts
    8,025

    Default Re: What's going on with this fuse box!????

    If the positive and negative supplies to the fuse box are both good and some unconnected outputs are 10.3v, Dave is correct in post #2, it can only be a faulty fuse box.

    £13 fuse panels from China ???
    Rainbow Marine.
    www.rainbowmarine.co.uk

  6. #6
    Join Date
    Apr 2013
    Location
    Nantwich, Cheshire
    Posts
    418

    Default Re: What's going on with this fuse box!????

    Yep I think you must be right! Thanks for the replies...
    Cutlass 27

  7. #7
    Join Date
    Sep 2001
    Location
    Me - Zumerzet Boat - Wareham
    Posts
    12,295

    Default Re: What's going on with this fuse box!????

    Quote Originally Posted by MarcJ View Post
    The feed to the fuse box is good 12.4V and the ground is good. What am I missing here, seems to defy the laws of physics!
    I wouldn't be very happy that you are only getting 12.4v at the fuse box!
    Does your battery need charging or are you getting at least 12.7v at the battery?
    MontyMariner.co.uk
    Facilitated by AWESEM WP Agency

  8. #8
    Join Date
    Apr 2013
    Location
    Nantwich, Cheshire
    Posts
    418

    Default Re: What's going on with this fuse box!????

    Quote Originally Posted by LadyInBed View Post
    I wouldn't be very happy that you are only getting 12.4v at the fuse box!
    Does your battery need charging or are you getting at least 12.7v at the battery?
    I'd been away for the weekend, so it was a bit down - probably would have got a higher reading directly at the battery. There's a 30W solar panel attached so no doubt after today's sunshine it'll be perking up! :-)
    Cutlass 27

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