Tow vehicle battery drained

TLC

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

N7SHG_Ham

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.

pthomas745

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.

TLC

Emergency brake cable wasn't pulled out.  Trailer battery full charge when first parked and full charged later.  

Sharon_is_SAM

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?

SweetlyHome

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?

MuttonChops

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)

ChanW

+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...

TLC

Thanks to all, this has been very helpful

Tundra57

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.