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Tow vehicle battery drained

TLCTLC Member Posts: 3
edited December 2020 in Battery/Electrical & Solar
New T@B owner here, non-mechanical person.  I would appreciate help,   we left our 2021 320 S Boondock connected to the tow vehicle for about a week.  When hubs went out to unconnect and use his truck (2001 Toyota Tacoma TRD) the battery on the Tacoma was dead.  So, even though there is solar and battery connection was turned off, the trailer drained the tow vehicle battery?  Cuz of e-brake? Phantom electrical usage?  Also.  When should the battery connection be turned off, only when trailer is not in use?   Thank you in advance
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  • N7SHG_HamN7SHG_Ham Member Posts: 1,261
    Hmm, doesn't seem right. With switch off, TV should be disconnected. With the solar the tab batteries would stay charged.

    The switch should be off for long term storage, on at all other times, battery will not charge from TV or shore power with switch off, NOR will trailer break away brakes be engaged if trailer was to part company from hitch while under way.

    2019 T@B 400 Boondock Lite
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  • pthomas745pthomas745 Moderator Posts: 3,942
    Was your emergency brake cable pulled out?  What is the status of the trailer's battery?  If the solar isn't charging the trailer battery, or it wasn't charged when parked,  then it will draw on the tow vehicle battery to charge itself.
    2017 Outback
    Towed by 2014 Touareg TDi
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  • TLCTLC Member Posts: 3
    Emergency brake cable wasn't pulled out.  Trailer battery full charge when first parked and full charged later.  
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  • Sharon_is_SAMSharon_is_SAM Administrator Posts: 9,732
    There was a recent post over on the TaG forum about a failed battery switch.  Disconnect from the truck, turn on a light in the TaB and then turn off the battery switch.  Did the light go off?
    Sharon / 2017 T@B CSS / 2015 Toyota Sienna Minivan / Westlake, Ohio
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  • SweetlyHomeSweetlyHome Member Posts: 336
    I've read this a couple of times but want to verify:

    The trailer was plugged in to the Tacoma and sat for about a week.

    The trailer battery switch was off.

    I assume the trailer is wired  with the solar connected directly to the trailer battery, by passing the shutoff.  This seems to be the Nucamp standard per other threads here in the forum. This keeps the battery charged in storage but is isolated otherwise from the tailer electric system.

    A guess based on the above:

    The Tacoma does not have an isolation relay. This means the TV was supporting the both its own phantom loads and the trailer's phantom loads depleting the TV battery.  How old was the Tacoma battery?
    Jupiter, Florida~T@B 400, with 2018 Toyota 4Runner

       
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  • MuttonChopsMuttonChops Member Posts: 1,698
    TLC said:
    . . . left our 2021 320 S Boondock connected to the tow vehicle for about a week.  When hubs went out to unconnect and use his truck (2001 Toyota Tacoma TRD) the battery on the Tacoma was dead. 

    IMHO your TV battery being dead is not a surprise.
    The 'phantom current draw' or baseline power consumption of things you can not fully turn-off PLUS nearly a week of TV & Trailer being idle is the reason.

    Every trailer will be different on baseline power consumption.  Mine varies between 300mA and 700mA with the difference being based on what items I remember to force off.  So over several days if 7-pin is connected to TV the Amp-Hour Drain really adds up.
    In 5 - 7 days it is not surprising the TV battery is very weak if not dead. as 36 - 118 AH of power have been drawn out.

    As for impact of Solar Panel and Cut-Off Switch.  Typical solar installation connects the panel directly to the battery.  While the Cut-Off Switch isolates the trailer battery from the baseline loads.  The (typical) wiring diagram below shows how the TV (via 7-pin) is always connected to the trailer 12VDC Panel even if the Cut-Off Switch is in 'battery off' position.
    In your case, after a week or so with Cut-Off 'off' and the 7-pin connected to the TV; TV has a dead battery while trailer has a fully charged battery.
    One must remember to disconnect the 7-pin.
    Or one has to install an isolation relay in the TV to stop the trailer from draining the TV battery (if 7-pin is connected and engine is no running)
    '18 320 S,  pitched axle, 3020HE; PNW based
    TV: '17 Colorado V6 Z71 4x4, Tow Package, GM Brake Controller
    Adventures:  54   Nights:  341  Towing Miles 43,780
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  • ChanWChanW Member Posts: 3,160
    edited November 2020
    +1 what @MuttonChops said. The battery cutoff switch doesn't 'break' the circuit between the 7-pin and the trailer power bus, it only cuts off the Tab's battery from the trailer. (Great explanation and illustration @MuttonChops)

    I installed an isolation relay in our Tacoma to protect against this. Pulling the 7-pin plug whenever your engine isn't running is another solution...
    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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  • TLCTLC Member Posts: 3
    Thanks to all, this has been very helpful
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  • Tundra57Tundra57 Member Posts: 640
    Just another option. I installed a Renogy battery charging unit at my Tab. It takes the battery voltage from the TV and used it to charge the battery in the correct manner to fully charge the tab battery. My Tundra would lower alternator voltage when its own battery was charged. So on a long run powering the fridge at night, i would stop and find the Tab batteries half drained.
    Now they are fully charged. The charger will not allow the tab to try and charge the TV. In my case, when ignition is off, the trailer plug is dead. However i ran a heavy duty feed directly to a winch disconnect plug on my tv. This is fed by an isolation winch relay. The umbilical is seperate from this plug to the tab side new Charger input. The output of the charger is connected to the trailer 12 v to the tab batteries (the connection box the trailer plug wires go into). The original input wire from the TV is disconnected and connected to the new charging unit enable input. So it will only charge if both the trailer plug and the additional feed wires are connected. Also the Tundra ignition has to be on and the winch relay isolation switch turned on.
    I have arranged power to the isolation relay switch to be fed from an ignition controlled source. So i can leave everything connected, but if the TV ignition is off no power flows in either direction.
    I have solar and a smartsolar BMV battery monitor and when on a run, my tv battery never drops below 98.8% according to the monitor.

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