Somebody Clear Up 12v Power From TV…Does it provide power?

manyman297

Ok, so my assumption was always that the 12v power in your 7-pin provided a little charge to your camper battery. 

On my last trip I noticed in my Victron SmartShunt app that my trailer battery was pushing power to my TV (roughly 100 watts or so). So it was doing the exact opposite. I get that the power can run both ways but what causes the camper battery to push power to your TV…or am I reading the Victron app incorrectly?

Jilong

Power flows from higher voltage to lower voltage. If the 12v wire from your 7-pin is directly connected to your trailer battery, then power can definitely flow the "other" way.

Grumpy_G

The 400BD has a solar panel right ? And what kind of battery/ies does it have ? As @Jilong wrote if the voltage is higher on the trailer side it can supply power to the TV. I'm not familiar with the charging system in the Taco but what might happen is that the TV sees a fairly high voltage and turns down the alternator output. So part of the TV electrical system power requirements is provided by the trailer.

manyman297

@Jilong Ahh, ok. That makes sense. @Grumpy_G yes I’m using solar so i’m wondering if the higher charge voltage is sending extra power to the TV? Is that how it works?

I have the two 6v AGM Harris batteries.

pthomas745

The Victron app is only measuring your trailer battery, not your tow vehicle battery.  If the solar panel on the trailer (you have about 190 watts of solar) was seeing 100 watts of solar, that would translate into about 8 amps of power going to the trailer battery....if the trailer battery needed that charge.

So, we need the rest of the story from the app: what was the shunt showing for "current?"  If that current number was a "negative" 8 amps or so, the solar would be sending power somewhere, first to the trailer battery. 

What you need to determine is if your tow vehicle has an "isolation relay" that would prevent this "backflow" to the tow vehicle battery.

https://tab-rv.vanillacommunity.com/discussion/10956/do-you-disconnect-the-electrical-plug-from-your-car-truck-when-stopping-for-an-hour-or-so-to-shop

But, what do I know?  This thread claims a Tacoma does not have an isolation relay. (I have no idea if the models are differently equipped).  I would take a closer look at this the next time you are on the road and examine what items were running in the trailer, what the solar input was, and what the "current" number was telling you.  Get a screen shot and lets see what it looks like.

https://tab-rv.vanillacommunity.com/discussion/12459/tow-vehicle-battery-drained

MuttonChops

Thinking about this from an Amperage source/demand viewpoint might help.

Some assumptions:
 --  Tow Vehicle real-world 7-pin can source 3'ish amps. "The trickle charge"
 --  Solar Panel might provide another 3'ish amps.
 --  TaB has a background current demand of 1 Amp or less. Things we can not turn off.
 --  Newer DCV compressor fridge draw ~9A when compressor is on
 --  The Victron Shunt is reporting Amps in/out of battery.

So:


Is the Shunt 'current out' due to Fridge draw what is really happening?

Horigan

Some of the current to the frig is being provided by the charging sources. 

Note that you can't really add up the charging amps from multiple chargers.  The charger with the least resistance will be the primary charger.  The other charger (alternator) will see the higher voltage from the other charger and think the battery is fully charged and not charge.