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twvette's avatar
twvette
Explorer
Dec 07, 2015

Main DC inline fuse and/or holder is melting

My Weekend Warrior toy hauler main DC power line has an inline fuse about foot away from battery and the fuse holder is getting really hot and starts to melt. It wont actually trip the fuse for a while even with the bulk of the fuse holder or fuse plastic itself melted. Just the fuse holder/fuse is getting hot for the most part, not the wiring for most part. This ONLY occurs when my Onan 5500 is running. I know when its about to happen as my charging voltage seen through my solar charging system is not very high (like 12.3v vs. normal 13 to 14V). It kills all DC power to the trailer when the fuse eventually does pop so it is my main line and the line the battery charge of generator comes through. Its 8ga wire and I inspected the wire runs and see nothing unusual or obvious shorting. Generator goes through an Iota DLS-45. This model says max output of 45 amps and the inline fuse was originally the large style maxi fuse 40 amp. Could the too small of fuse cause the heat? Seems a little unlikely as doubt it really is at max output.

To get through my last trip I sparingly ran the generator and wired in a more typical ATO size inline fuse holder. The max amp fuse I could get again was a 40 amp. This fuse holder was not melting but was also getting very hot but the fuse plastic itself melts internally and will also eventually pop the fuse.

Just too small of fuse? Maybe I had really bad luck with two separate fuse holders not making good contact and high resistance creating heat (second one was a friends used one from bottom of his tool box but seemed in good shape)?

I am taking with me next time I go camping (toy hauler in storage far away) a thermal imager to inspect all wiring and a DC amp clamp to do some more better troubleshooting but wanted to pick some brains of things to look for? I did purchase a 50a circuit breaker that is probably much better than an inline fuse anyway and if nothing else will save me from going through a bunch of fuses.

I have not changed anything on the electrical for a long time now so a bit baffled. There is a solar system (just one panel) and I do have a 2k inverter but nothing gets hot unless the generator is also running.
Toy Haulers
  • twvette's avatar
    twvette
    Explorer
    Jan 11, 2016
    Finally got back around to this and some time to play with my Infrared imager.

    Did a week long trip and first two days my fuse was not getting hot at all and voltages were good to reflect this.

    On the third day started to notice voltages dropping off so knew it was likely happening again and it sure was .. wow that is hot:

    This is combo IR and visual image blended. You can see the orange colored fuse is not the hottest, its down in the body of the fuse holder that is really hot. Its a little deceiving to determine actual temps from the colors as the fuse was hot to the touch where looks "cold" in the image but still lets you know where the source is. The blue leg going down towards the bottom is the DC line so it has some heat in it too but it fades off with distance from the fuse holder.

    Here is IR only:

    To me this just further confirms the source is in the fuse body. If I were able to get to it before it heat soaked I think it would probably better pinpoint the problematic area in the body.

    There was nothing different between the first two days and the third except time. In other words nothing different that I turned on, etc. or used for a longer duration that I think would be significant. This is also what I observed last trip ... no issues until some time had passed.

    For some reason I could not get my new amp clamp to read DC amps or voltage on this line. Would have liked to have seen this info to see what was going on with it too. Single conductor + DC line so not sure why nothing read.

    Scanned all my electrical system with the IR imager and nothing else was getting hot. Still went ahead and tied some of the main lines connected with twist connectors to nice bus connector for further confidence and mounted them properly to hopefully ensure nothing ever shorts them out.

    Installed the new circuit breaker and no problems the remaining 3-4 days and could even see an improvement in charging voltage in general.

    Hopefully this is the end of this problem ;)
  • twvette's avatar
    twvette
    Explorer
    Dec 13, 2015
    Thanks everyone. As mentioned initially, I have a breaker to replace the inline fuse on order and I went with a Bussman 50amp breaker:
    http://www.amazon.com/gp/product/B0024JHQ02?psc=1&redirect=true&ref_=oh_aui_detailpage_o05_s00

    I also failed to mention I did see two sets of multiple power lines connected together with the twist type connectors in my electrical compartment. I assume this is where previous owner tied in the non-factory inverter. I have never been a fan of this connector type (no real reason, just seem least reliable to me) so will redo these with a bus bar and terminal rings on the wires incase it is a high resistance area or similar. These are far away from my problematic fuse holder and did not seem to be getting hot but I just don't like it so will improve it while messing around with electrical stuff:
    http://www.amazon.com/gp/product/B0051P1L52?psc=1&redirect=true&ref_=oh_aui_detailpage_o06_s00

    Looking forward to what I find with my new amp clamp and thermal imager so will post some numbers/pics in a few weeks.
  • allcool's avatar
    allcool
    Explorer
    Dec 08, 2015
    twvette wrote:


    I am taking with me next time I go camping (toy hauler in storage far away) a thermal imager to inspect all wiring and a DC amp clamp to do some more better troubleshooting but wanted to pick some brains of things to look for? I did purchase a 50a circuit breaker that is probably much better than an inline fuse anyway and if nothing else will save me from going through a bunch of fuses.
    Good idea getting a circuit breaker and using a amp meter. Get everything on and running/charging to take max amp draw reading. Wonder if the genny running the convertor, and the solar charging system, are both on at the same time and overloading the circuit...?


    I have not changed anything on the electrical for a long time now so a bit baffled. There is a solar system (just one panel) and I do have a 2k inverter but nothing gets hot unless the generator is also running.



    If the wire to the fuse is not getting hot or melted, but the fuse/ holder is melting, can only be a couple of things.
    Either a bad connection between fuse and fuse holder, or fuse/holder is close to the max amp draw it is designed/rated for.

    Not uncommon for a fuse holder continuously being used at close to max rated amperage, or one with compromised connections,to get very hot and maybe actually melt a little, I've seen that many times...

    jmo
  • eHoefler's avatar
    eHoefler
    Explorer II
    Dec 07, 2015
    beemerphile1 wrote:
    Loose and/or poor connection causes arcing and arcing causes heat. Cut out the fuse holder and install a new one with the correct size fuse.


    Or replace it with a breaker with studs. Having a nut tightened down on it will ensure a tight connection.
  • beemerphile1's avatar
    beemerphile1
    Explorer
    Dec 07, 2015
    Loose and/or poor connection causes arcing and arcing causes heat. Cut out the fuse holder and install a new one with the correct size fuse.
  • RoyB's avatar
    RoyB
    Explorer II
    Dec 07, 2015
    Apparently from your description of failure you are not exceeding the rated value of the fuse otherwise the fuse would blow and open the circuit.

    Your would expect the fuse to blow if something is melting your wiring and fuse holder...

    If this is the fuse assy close to the battery terminals its function is to protect the wiring more than providing system protection.

    Almost has to be associated with too small of wiring or under rated fuse holder for the amount of current being used.

    This may not be your problem but alot of times when folks upgrade their converter/charger from the original OEM 25-30 DC AMPS model to a 45-55 DC Amps model and they do not replace the wiring or the inline fuse assy to a larger rated size between the converter/charger and the battery connection.

    Roy Ken
  • enblethen's avatar
    enblethen
    Nomad
    Dec 07, 2015
    It could be just the fuse holder. many have very small wire that is not capable of handling the full load.
    I would switch the fuse holder out to a auto-resetting circuit breaker. Attach the main wires to it with out reducing the conductor size.
    You need to check the size of the conductor and size the circuit breaker for the smallest one. Hopefully the smallest in at least a #6. You could then install a forty or even a fifty amp circuit breaker.

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