Blown 30amp fuses - repeated issue

Hi all - relatively new Tab 320 owner here… twice now we have gone to disconnect at a campsite and found one of the 30amp fuses blown, rendering battery useless. 

Is this just general wear and tear after a year of use, or something else? 

We tow with battery in “on” position and fridge running. Any correlation? Is that the wrong thing to do? 

Any help much appreciated!


  • ChrisKChrisK Member Posts: 238
    We tow just like that all the time. Is it blowing when you hook up or disconnect?
  • LisaBillingsLisaBillings Member Posts: 7
    Ok great, thank you Chris! Glad to know we are doing that part right (this is a point of argument between us so I’m glad I’m right LOL)!!!! We don’t really know to be honest - it all seems fine when we hook up and then when we get to our destination it’s blown! 
  • Grumpy_GGrumpy_G Member Posts: 214
    Does the tow vehicle have a fuse for the 12V trailer power and have you checked if it is blown as well ? I'm thinking there may be an intermittent short (wire rubbed through or similar) that blows the fuse when you're towing it. 
  • LisaBillingsLisaBillings Member Posts: 7
    Thank you G! This is a good question - do you have any idea how we would know? Would this be associated with the tow package or the Subaru Outback? Tow package also has a manual braking feature - situated inside the car that supports the trailer braking on downhills …any possible issue with that? 
  • pthomas745pthomas745 Moderator Posts: 2,718
    This is happening when "disconnecting" from shore power or "connecting?"  Do you know what the state of charge of your battery is when you "connect?"  I would guess that the fuses are blowing when connecting to shore power.  You don't notice it because shore power is powering all the devices in the trailer.
    Do you know your battery state of charge?  If the battery is depleted, and then plugged in, it might be blowing that fuse right away.  A bad 30 amp fuse would not allow the battery to charge back up on shore power.
    You would need to sort this sequence out. 
    2017 Outback
    Towed by 2014 Touareg TDi
  • Denny16Denny16 Member Posts: 4,774
    edited August 5
    A tip to prevent surge power spikes when connecting and disconnecting a trailer from shore power — Do the following when hooking up or unhooking external shore power:
     1.  Turn off Alde and CoolCat, and any other 120VAC appliances you are running. 
     2.  Make sure the Inverter (TaB 400 one is standard)
     3.  Turn off 12VDC Battery disconnect switch (optional by a good idea)
     4.  This is the big one, make sure you turn off the circuit breakers in the shore power pedestal, Before  connecting the shore power cable to the pedestal.  Connect the cord to the TaB first and then to the pedestal with its power shut off. 
    This should prevent blown fuses and circuit breakers in your TaB.  
    After connecting the shore power cable, you can turn on the pedestal breakers, then turn on Alde and any other appliances you need, one at a time.

    Do the opposite when disconnecting, and Bob’s your uncle... 
    2018 TaB400 Custom Boondock,  Jeep Gladiator truck, Northern California Coast.
  • Sharon_is_SAMSharon_is_SAM Administrator Posts: 8,669
    Not sure if it has any impact on the 12V battery fuse, but are you using a surge protector while on shorepower?
    Sharon / 2017 [email protected] CSS / 2015 Toyota Sienna Minivan / Westlake, Ohio
  • tybladesmithtybladesmith Member Posts: 161
    @LisaBillings is the fuse that is blowing at the battery?
    If the battery is way low from running the fridge on 12vdc while towing, the charge line from the tow vehicle may not be keeping up with fridge amp draw. Maybe when you connect to shore power the battery will take all of 30 amps or 35 depending on output from converter, blowing the fuse. 
    My 30A fuse holder at battery needs to be replaced due to this overheating. I went through 3 30A fuses before the fuse held and the battery kept charging. Just my experience once. YMMV
    What is your towing vehicle?
    Kay and Tom - SW Wisconsin - Silver [email protected] - 2018 [email protected] 320S Boondock Silver/Black trim TV, 2018 Chevy Colorado, Silver/Black trim, Duramax, TowHaul, IntelliHaul
  • MuttonChopsMuttonChops Member Posts: 1,234
    edited August 5
    LisaBillings said:
    . . . new Tab 320 owner here… twice now we have gone to disconnect at a campsite and found one of the 30amp fuses blown, rendering battery useless.

    Is this just general wear and tear after a year of use, or something else?
    As you might have guessed from the earlier replies . . . having the 30 Amp fuses blowing is not common.
    Something is wrong.

    In general there are three 30 Amp (or above fuses) in the trailer:
      1)  an in-line fuse on the battery positive terminal
      2)  a 'Battery' 30 Amp fuse at the Power Center DC Fuse Panel
      3)  a 40 Amp fuse for reverse polarity protection also at Power Center DC Fuse Panel

    Which Fuse(s) are Failing?  And when do they Fail ?

    Something more than new user "oh darn" sequence of events is causing the fuse(s) to blow.
    '18 320 Spitched axle, 3020HE; PNW based
    TV: '17 Colorado V6 Z71 4x4, Tow Package, GM Brake Controller
    Adventures:  41   Nights:  240 
  • LisaBillingsLisaBillings Member Posts: 7
    Thank you everyone for all your input! We have racked our brains using your comments and think something may be wrong when towing with battery on. The last time we blew the fuse (second time in one trip), we had been dry camping with brand new fuse and good battery charge, hooked up to the car (Subaru Outback), got it home and the fuse was blown. No shore power involved at all, and on that trip battery was in “on” but fridge was off. 

    The 30 Amp that keeps blowing is in-line fuse at positive battery terminal.

    I’m thinking we need to investigate something wrong with the tow vehicle hookup. Any recommendations on that? 

    BTW, very unsatisfactory answer from RV dealer on this topic…thankful for this forum and your expertise! 
  • VictoriaPVictoriaP Member Posts: 1,313
    edited August 9
    @LisaBillings As there has never been a “tow package” for the Subaru Outback (only a hitch with 4 pin wiring not suitable for trailer brakes), I have to ask who you had install your 12v line and 7 pin plug on the vehicle. It’s extremely rare for Subaru dealers to install them for Outbacks, they’ll only install the stock flat 4 pin connector, so I’m guessing you had a third party do it. That installer should be contacted to help you triage, because you do not ever want to tow without the battery on; it’s needed to power your trailer’s emergency braking system in the event the trailer comes off the hitch ball. 

    Some other questions: Did it ever work correctly, or has it always blown the fuse every time? Does it blow immediately when plugged in, or does it only happen after towing for a time? What brake controller are you using (hard wired, or wireless) to control the brakes while towing? Have you tried it with another vehicle? (Perhaps a friend or a nearby Tab owner could assist.) 

    In general, when asking for help, it’s also useful for us to know the year and model/trim level of both vehicle and trailer, as different model years can have very different configurations. For your specific issue, knowing the battery type on the trailer may also be helpful, as traditional lead acid charges at different rates than an AGM or lithium…and that may be coming into play when the battery tries to pull from the alternator or vice versa.
    2019 320s BD Lite, white with blue (“Haven”)
    2015 Subaru Outback 3.6r (unsafe 200lb tongue weight limit until 2020 models)
    2020 Subaru Outback XT
    Pacific NW
Sign In or Register to comment.