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Technical Why do I keep blowing 30 amp fuses??

Discussion in 'The Hokey Ass Message Board' started by seadog, May 19, 2019.

  1. Recently I’ve blown 4 30 amp fuses in quick succession. Need your thoughts on what to check next.

    Here’s the background. Deuce Roadster with an American Autowire 15 circuit wiring kit. Wired by me and everything worked as it should till about a month ago when one of the “accessory” circuits started blowing 30 amp fuses. This circuit supplies power to a cigarette plug charger receptacle between the seats. I use it to power a phone and that’s all.

    About a month ago I noticed the phone wasn’t charging, checked and found the fuse was blown. Replaced fuse...drove the car for a stopped charging...fuse get the picture.

    Yesterday, driving back from Steel In Motion, I hit the mother of all railroad crossings. The car bottomed out and stalled. I restarted, cussed a bit, and noticed the phone wasn’t charging. When I got home I checked and the fuse was blown.

    Anybody have any suggestions/thoughts on what’s going on. I always thought that a power surge was the cause of a blown fuse, but I don’t think the phone charger would have that much of a draw. I’ve heard bad things about China accessory chargers. Maybe I should just start by replacing the charger?
  2. Doublepumper
    Joined: Jun 26, 2016
    Posts: 293


    I'd start by tracing the wiring from the power port back to the fuse panel. Sounds like you have a power wire shorting out to ground somewhere.
  3. Boneyard51
    Joined: Dec 10, 2017
    Posts: 1,990


    Because you are getting 31 amps or more!!! No just kidding, when you hit the tracks something shorted out. That is something touched something it shouldn’t.

    loudbang, XXL__, deathrowdave and 2 others like this.
  4. Dick Stevens
    Joined: Aug 7, 2012
    Posts: 2,489

    Dick Stevens

    That circuit has a short in it somewhere, as has been stated you need to trace the wiring the full distance it runs or the cigarette lighter socket itself could be shoring out!
    loudbang, INVISIBLEKID and Hamtown Al like this.
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  5. spanners
    Joined: Feb 24, 2009
    Posts: 724


    30 amp fuse in a cicarette lighter socket sounds excessive to start with to me. If your 'phone charger had a hiccup it would melt before the fuse blew.
    It sounds like a dead short, possibly caught under the seat riser and when you saddle up for a drive it's pinching it.
    clem, loudbang, XXL__ and 3 others like this.
  6. noboD
    Joined: Jan 29, 2004
    Posts: 6,791


    Contact 37Kid on here, he's a master at electricity.
    Sandgroper, loudbang, RICH B and 3 others like this.
  7. TrailerTrashToo
    Joined: Jun 20, 2018
    Posts: 290


    Also, I have had the cigarette lighter receptacle short out internally. The cigarette lighter receptacle would only short out when something was plugged into it. Going to to take some troubleshooting using a multi-meter to check resistance to ground.

    In order of probability:

    1. Wire from fuse panel grounded to metal (insulation rubbed off) - disconnect the hot wire (+12 Volts) from cigarette lighter receptacle - if you keep blowing 30 Amp fuses - the wire is shorted to metal (ground) somewhere
    2. Internal failure of the cigarette lighter receptacle
    3. Internal failure of the phone charger
    loudbang and Truck64 like this.
  8. Mr48chev
    Joined: Dec 28, 2007
    Posts: 24,693


    I'd have to believe that you answered your own question when you said it blew the fuse when you went over the bump. Loose connection or a wire with a bare spot that shorts out at times. If you don't use it for a lighter you don't need or want that heavy of fuse. Phones draw way under 5 amps to charge them at least on mine.

    Sent from my VS988 using The H.A.M.B. mobile app
    clem and loudbang like this.
  9. Truck64
    Joined: Oct 18, 2015
    Posts: 3,064

    from Ioway

    Cigar lighter receptacle (charging port or whatever it's called these days) shorting to hot would be the first thing to look at. Bypass it, remove it, see if it goes away.
    loudbang likes this.
  10. Tom, I have the same wiring kit and we also use a 30 amp fuse for the Garman and phone, I haven't experienced any problems.

    I'm just spitballing but you may just have a bad lighter port or a loose connection. HRP
  11. Dangerous Dan
    Joined: Jul 10, 2011
    Posts: 304

    Dangerous Dan
    from Graham Wa.

    You don't have a short, you have a long LOL
  12. zzford
    Joined: May 5, 2005
    Posts: 1,822


    I would disconnect the charging port at the port itself, first. If it still kills the fuse, start chasing it from there.
    seb fontana likes this.
  13. Mike Colemire
    Joined: May 18, 2013
    Posts: 858

    Mike Colemire

    I used to replace several lighter assy in fords, something about the phone chargers they use or the way they jerked them out would screw them up and they'd blow a fuse.
    loudbang, Dog_Patch and jimmy six like this.
  14. 29moonshine
    Joined: Dec 30, 2006
    Posts: 1,254


    disconnect the wire from the port if it still blows it in the wire if not in is the port
    seb fontana and INVISIBLEKID like this.
  15. Brand Apart
    Joined: Jan 22, 2011
    Posts: 540

    Brand Apart
    from Roswell GA

    Yeah disconnect the wire and let the terminal flop around behind your dash I'm sure that won't hit anything metal and short out. Sarcasm here.

    sorry not much help I can offer that hasn't been said already
  16. BamaMav
    Joined: Jun 19, 2011
    Posts: 2,928

    from Berry, AL

    If you’re just using it for charging a phone or the like and not using an actual cig lighter, replace it with a charge port. They are made different with solid walls where the lighter sockets are split and springy to hold the lighter elements in until they get hot enough to jump out. The smooth wall in the charge port doesn’t grab the side connectors on the plugs like a lighter socket does, and is not as likely to get bent and short out.
    loudbang, XXL__ and squirrel like this.
  17. squirrel
    Joined: Sep 23, 2004
    Posts: 42,260


    take the lighter socket out and look at it, both ends, you'll probably see where it arc'd when it blew the fuse.
    Lil32 likes this.
  18. 31 Chopped Coupe
    Joined: Aug 24, 2014
    Posts: 65

    31 Chopped Coupe

    I had the same issue, it turned out to be the lighter socket.
    dan31 likes this.
  19. H380
    Joined: Sep 20, 2015
    Posts: 383

    from Louisiana

    Found a penny flat in the bottom of a cigarette lighter hole once
  20. It has been said above but check the socket carefully. I had the exact situation on an OT car. I found corrosion inside the socket. I unplugged it, replaced the fuse and all OK. The fix was to replace the plug assembly.
    olscrounger likes this.
  21. thecj3man
    Joined: Aug 16, 2010
    Posts: 14

    from TN

    I put a new lighter plug in my 55 last winter that has the fuse about 4” from the termination on the plug. For some reason my Garmin blows the fuse, almost always upon unplugging it. I am starting to think it is something with the 12V power supply instead of the car wiring.
  22. Phone chargers are usually 2.1 A. Disconnect power port, then wiggle wire or test drive. It's most likely the lighter socket, but it can be the wire leading to it. I also use a usb power port (better then the lighter port and less chance for something to fall in).

    loudbang likes this.
  23. Ziggster
    Joined: Aug 27, 2018
    Posts: 183


    As others have said, 30A fuse for a circuit dedicated for a cigarette lighter is too much. Fuses are meant to prevent wires from melting, and therefore the wires in the circuit should be rated accordingly. I have a 1/2 Hp electrically powered air compressor on my truck rated at 30A and it has a dedicated breaker. It likely is the adapter itself or check for wires where they pass through the firewall. Lots of electrical issues can be traced to wires that wear as they pass through metal and also melt due to heat from the engine.
    loudbang and XXL__ like this.
  24. XXL__
    Joined: Dec 28, 2009
    Posts: 1,643


    That is WAY too much fuse.

    Garmin specs either a 1A or 2A fuse, depending on model. A 36 watt phone charger (read as-- an unusually large one, capable of fast-charging 2 devices at once) uses a 5A fuse (36W/12V=3A actual draw... with another 2A overhead). If you run both the Garmin and a very large charger at the same time, you're at 7A with full overhead.

    As an example, typical 60's through 80's GM vehicle, which had cigarette lighter, clock, dome lamp, and cargo lamp all on the same circuit... was only a 20A fuse... and they engineered for the possibility that you'd have all of those on at the same time.

    /2 cents
  25. ^^^^^ A dead short don't care.
  26. XXL__
    Joined: Dec 28, 2009
    Posts: 1,643


    Of course, but the more common failure mode is less drastic, which is why manufacturers use different size fuses for different circuits... instead of just slapping 30's in everything . The OP likely has a dead short. My previous post was to @HOTRODPRIMER and his setup.
  27. Aftermarket and OEM are not the same thing.
  28. XXL__
    Joined: Dec 28, 2009
    Posts: 1,643


    What does this even mean? P=IV is universal.
  29. reefer
    Joined: Oct 17, 2001
    Posts: 729


    Have a look at the blown fuse... if it’s just got a little blob/ break in the wire it is usually overload where the wire has got to melting point and parted, if it is blown to smithereens it’s a dead short usually, the sudden surge just blows it to bits.
    Might help narrow it down.
    Johnny Gee likes this.

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