12V power to trailer when towing

EWizard
EWizard Member Posts: 106
edited March 2016 in Battery/Electrical & Solar
Hey ya'll.
I just got back from my 2005 T@B's maiden camping voyage last weekend.
It did great, but I do have one question though.  
I was plugged into shore power before leaving, and while camping but had to turn my fridge on battery before leaving the house, and leaving the campsite.
My battery was fully charged before leaving each time.  When I got home this weekend my battery was 11.4V.  :-(
I tested my 7-way plug on my TV and when not running I'm getting 12.4V and 13.9 when the engine is running.
Shore power appears to be charging my T@B battery fine, but when towing I'm not getting the juice I need to the the battery.

I have not opened the junction box on the bottom of the T@B yet to see where the breakdown is occurring.
Do you all upgrade your 12V power cable coming from the TV's battery to the 7-way plug?
Or is there some place on the T@B that is known to keep your battery from charging?

Thanks in advance!

Eric in Austin.
2005 T@B U model
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Comments

  • jkjenn
    jkjenn Member Posts: 6,417
    EWizard said:
    Hey ya'll.
    I just got back from my 2005 T@B's maiden camping voyage last weekend.
    It did great, but I do have one question though.  
    I was plugged into shore power before leaving, and while camping but had to turn my fridge on battery before leaving the house, and leaving the campsite.
    My battery was fully charged before leaving each time.  When I got home this weekend my battery was 11.4V.  :-(
    I tested my 7-way plug on my TV and when not running I'm getting 12.4V and 13.9 when the engine is running.
    Shore power appears to be charging my T@B battery fine, but when towing I'm not getting the juice I need to the the battery.

    I have not opened the junction box on the bottom of the T@B yet to see where the breakdown is occurring.
    Do you all upgrade your 12V power cable coming from the TV's battery to the 7-way plug?
    Or is there some place on the T@B that is known to keep your battery from charging?

    Thanks in advance!

    Eric in Austin.
    Congrats on the maiden voyage! 2 questions for you. First, how far did you drive. Second, do you have a battery cut off switch?

    I ask those questions out of an abundance of caution, but it is either a weak alternator or the wire isn't sufficient. How many amps is your alternator? My first TV had a 140AH alternator and it couldn't keep up with the fridge. A simple solution was to turn off the fridge for part of the trip. Your food will stay cold for quite a while because the fridge is well insulated.


    2021 T@b 320 Boondock "Mattie Ross" | 2021 T@b Nights: 239 | Total nights in a T@b 455 | 2022 Jeep Grand Cherokee L Overland | T@b owner since 2014

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  • EWizard
    EWizard Member Posts: 106
    ~4 hour drive, and yes I have a battery cut off switch.
    Not sue how many amp hours my alternator puts out but it's a stock alternator on a 2008 Toyota Sienna.  A little Google searching says 130ah.

    2005 T@B U model
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  • EWizard
    EWizard Member Posts: 106
    I've been Googling a little and it seems like most RV'ers run their refrigerators on propane while towing.
    Is this acceptable?
    2005 T@B U model
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  • Nomad
    Nomad Member Posts: 7,209
    From everything I've read you shouldn't run your T@B on propane while traveling - I believe it's because the fridge vents are on the front of the T@B so the flame can get blown out and your little T@B becomes a big propane resevoiur. The RVs your reading about probably have side vents.
    Sounds like your alternator is smaller than Jenn's old one. I have a Jeep like Jenn had and mine usually does just fine keeping the battery charged and the fridge running. The only difference we could figure out was mine had the factory tow package with a larger alternator and Jenn's was an add on tow.
    Some people having this problem throw a bag of ice inside and turn the fridge off while traveling.
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  • source3
    source3 Member Posts: 144
    You may have answered your own question about wire gauge for battery - minimum of 10 gauge.  If you turn off your car for more than 30 minutes you want to turn off your fridge if running on 12v.  It will drain the trailer and car battery (if you do not have a cutoff switch) within an hour.  I have my car wired to turn off the battery terminal on trailer socket when car is off.  Or you can install a kill switch next to the trailer battery to kill all power to trailer.  Many options.

    Initial thoughts.
    Have your alternator tested.  You can do it yourself if you are handy with a multi-meter.  I am running a Toyota stock alternator at 130 amps no problem and run fridge on 12v when driving.  Another common overlook is what else are you running off of your alternator.  In-car dvd, AC, extra lights, laptops, GPS/navigation, radar detector, etc.  All this adds up and puts a strain on the alternator; you may need a high amp alternator.  Perhaps your alternator has no remaining amps to charge the trailer battery.

    What is the voltage of the trailer battery when when car is off and trailer plugged in to tow vehicle?  Around 12.8 volts?  What is the voltage of trailer battery when car is running and trailer plugged into tow vehicle?  13.8 to 14.2 volts?  With car running and all accessories off, you your car battery and trailer battery should be about the same, 13.8 to 14.2 volts.  


    Andrew P. 
    Durango, CO
    2015 S Outback

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  • jkjenn
    jkjenn Member Posts: 6,417
    EWizard said:
    ~4 hour drive, and yes I have a battery cut off switch.
    Not sue how many amp hours my alternator puts out but it's a stock alternator on a 2008 Toyota Sienna.  A little Google searching says 130ah.

    130AH is not going to keep up with your fridge. Changing the charge wire may help, but I am not sure it will really do it. I am sure some of the engineers here know. 4 hours is definitely long enough to run the battery down.

    PXLated said:
    From everything I've read you shouldn't run your T@B on propane while traveling - I believe it's because the fridge vents are on the front of the T@B so the flame can get blown out and your little T@B becomes a big propane resevoiur. The RVs your reading about probably have side vents.
    Sounds like your alternator is smaller than Jenn's old one. I have a Jeep like Jenn had and mine usually does just fine keeping the battery charged and the fridge running. The only difference we could figure out was mine had the factory tow package with a larger alternator and Jenn's was an add on tow.
    Some people having this problem throw a bag of ice inside and turn the fridge off while traveling.
    @PXLatedis running a 160AH alternator, so enough juice to keep things going. The alternator seems to be one of those things car manufacturer change out regularly.

    My dealer recommended running on LP, but I just don't like the idea, myself and many caution against it. What I did last year is alternate turning fridge on/off every few hours, but you can easily go 4 hours and your food will still be cold.  I spent about 18 days on the road like that and had no issues. The bottle of water that was frozen when I left was frozen when I returned home.

    2021 T@b 320 Boondock "Mattie Ross" | 2021 T@b Nights: 239 | Total nights in a T@b 455 | 2022 Jeep Grand Cherokee L Overland | T@b owner since 2014

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  • Ron
    Ron Member Posts: 137
    I think the problem is that the hot 12v wires are to small for the length of the run.  The factory wires are meant to keep the very small break-away batteries on trailers charged.
    I ran a separate pair of #10 wires from a 30 amp circut breaker by the TV battery to a 30 amp fuse on the TaB battery.  TaB battery shows much higher voltage with this wire connected than with just the factory trailer wiring connected.  TV is 2012 Jeep JK Rubicon that is listed as having a 160 amp alternator.
    2016 T@B MaxS, 2018 Jeep Rubicon 4dr, Rural Scottsdale, Az.
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  • source3
    source3 Member Posts: 144
    If you are going to re-wire, run #8 or #10 wire from the battery into a 25 amp fuse/relay (http://www.delcity.net/store/Hella-Mini-ISO-Relays-with-Fuse/p_808962) then to the trailer socket.  The relay is controlled (on/off) by the ignition fuse (pigtailed from the ignition fuse). This will prevent the trailer socket battery terminal being hot when car is off, hence no battery drain on tow vehicle. 

    Then source a high output alternator.  See if your engine matches another toyota truck and buy a Mean Green (http://shop.mean-green.com/TOYOTA_c7.htm).  And buy a high quality car battery.  You may have room in the engine bay to buy a larger battery.
    Andrew P. 
    Durango, CO
    2015 S Outback

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  • Dalehelman
    Dalehelman Member Posts: 2,414
    In over 40 years of RVing in all types of RVs. We have always traveled with the frig running on propane. In the event the flame blows out the propane will automatically shut off. In cold weather we also travel with the Alde on as well. Our T@b is the first unit to have a 3 way frig. We have used it on 12 volts on occasion to save on propane.
    1. Hash  T@B Fun
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  • Tabster
    Tabster Member Posts: 118
    Camping last week in the pouring rain. Couldn't use my solar panels. 4 day trip and was running low on battery power. Plugged into my TV (ford f-150) and ran the engine for an hour. Fully charged. Gas gauge on the truck didn't drop at all. 
    2015 CS. Ford f150 v8. Southern california
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  • Nomad
    Nomad Member Posts: 7,209
    Dalehelman - Every discussion here I've seen about running propane while on the road has said not to do it - I've followed that advice and will continue.
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  • EWizard
    EWizard Member Posts: 106
    The 7 way plug on my Sienna was added just before we picked up the T@B.
    The "auxiliary 12v power" wire on the plug is very small, like #14.
    I'm familiar enough with relays (and isolators) so I could install one in the engine bay of my TV, then run a dedicated #10 (or #8) out to the 7 way plug.
    I'm sure this would help tremendously.
    2005 T@B U model
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  • EWizard
    EWizard Member Posts: 106
    edited March 2016
    Here we go!
    http://www.expeditionportal.com/forum/threads/77503-How-to-make-a-cheap-isolated-dual-battery-setup-for-50
    Only instead of going directly to the battery on the T@B, I will go into the 7 way plug.
    And 4 gauge is overkill.  Will scale down to 8 gauge on the auxilliary side.
    2005 T@B U model
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  • ChanW
    ChanW Member Posts: 3,165
    EWiz, just to clarify, I'm pretty sure that the center conductor, sometimes called the 'auxiliary', in the 7pin is unused in the Tab.

    The one that needs to be heavy is the 'battery' or 'charging' conductor, #4, as well as the ground wire, #1.

    Here's a pic:

    Chan  -  near Buffalo NY
    2014 S Maxx
    2011 Tacoma 4cyl ... edit: 2022 Tacoma 6cyl - oh yeah! 

     A_Little_T@b'll_Do_Ya
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  • EWizard
    EWizard Member Posts: 106
    edited March 2016
    Interesting.  I always wondered how people did this running light thing when parked.
    I tested pin 4 (+) and pin 1 (-) with my DMM last night and measuered 12.4 when my TV was turned off, and 13.9 when running.  The amperage has to be minimal because the wires are so tiny.
    2005 T@B U model
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  • jkjenn
    jkjenn Member Posts: 6,417
    EWizard said:
    The 7 way plug on my Sienna was added just before we picked up the T@B.
    The "auxiliary 12v power" wire on the plug is very small, like #14.
    I'm familiar enough with relays (and isolators) so I could install one in the engine bay of my TV, then run a dedicated #10 (or #8) out to the 7 way plug.
    I'm sure this would help tremendously.
    #14 wiring _ 130AH alternator will definitely keep you TV from charging your battery with the fridge on.

    2021 T@b 320 Boondock "Mattie Ross" | 2021 T@b Nights: 239 | Total nights in a T@b 455 | 2022 Jeep Grand Cherokee L Overland | T@b owner since 2014

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