Controlling the Charge from a TV

[Omnial]

I'm looking for clarity on the subject of charging from your TV. I've seen many posts discussing the limitations of connecting via the 7-Pin due to inadequate wire size in the vehicle. And I've seen many solutions involving beefing up the wiring, etc. to get more amps to the trailer batteries.

But I've not seen guidance about controlling the charge from a TV. Considering that solar charge controllers and AC chargers have 'smarts' built in to vary the voltage through bulk, absorption, and float modes, should not the power coming from a TV be similarly controlled?

I've seen many posts where people have upgraded their 12v systems with increased battery capacity, adding solar, new MPPT controllers, battery monitors, new inverter/chargers, etc. But even in those most sophisticated upgrades (with all the Victron goodies), the TV charge cable just run into the bus bar or at best, into something like the Orion DC to DC controller that lets you specify a fixed output voltage.

So, why is a 'smart' charge controller NOT needed in between the TV charge cable and the battery... or is it?

[A W Warn]

The tow vehicle has its own voltage regulation, to protect its electrical system. No need for duplication.

IMO, the charge wire from the tow vehicle is intended to maintain battery charge while at the same time traveling using fridge & furnace on propane. I think it is not intended to recharge the trailer's batteries while camping (though it will, but very slowly)

[Fair_Enough]

In my humble observation the voltage on B+ between TV and trailer is usually far lower than optimum for the trailer batteries. No need for control. It does basically nothing. If you seriously want to charge from TV, design the circuit for less than 3% voltage drop from alternator to trailer batteries, run heavier gauge cabling and employ a good DC -DC converter such as those sold by Sterling. Lots of info on the web. Look at well designed camper vans. Or have a solar system that charges while traveling, can even run the fridge, letting you arrive with fully charged batteries. If you actually want to charge off the TV in a pinch, turn it around and use jumper cables, battery to battery. But that has to be the worst possible method, energy wise. Clint

[r carl]

I would think the charge wire from tow vehicle is to charge the small battery for the break away switch on some trailers.

[gator.bigfoot]

I don't think it is wise to charge a large amount of batteries with the TV. Even if you up size the wire you still have at least one connector in the path. The amount of current you are going to need to charge the batteries properly are going to be an issue. Without up sizing the wires you will inevitably have a huge voltage drop which in turn will not charge your batteries properly (if at all). Even if you solve the voltage drop by up sizing the wire you will reduce the reliability of the connector with the amount of current which will most likely cause it to fail. If you are just charging one small battery you might get away with it, but if that is the only charging source your batteries will have a short life since they are never really getting fully charged.

If you have a solar installation then your solar array will be charging your batteries. If your solar installation is done properly with the correct wire sizes and proper connectors with a decent charge controller then your batteries are going to get charged properly and live a longer life. Whether you connect to your TV or not the solar charger will most likely provide the charge that you need and not the TV. Even you drive through the night your batteries would have already been charged properly during the day with the solar charge controller so very little charge (if any) will be needed.

IMO it is a waste of time and money to up size the wire of the TV. Invest in a proper charge controller (solar or other) and go with the largest size of wire that you need. Keeping your charge controller as close to your batteries will save on wire and reduce your cost. Also invest in a battery monitor (BMS) so that you will always know your state of charge (SOC) and what you are using. Even with a small solar array (100 watts) you are better off than trying to use the TV. For around $800 CDN you could get one solar panel and a Trimetric 2030 BMS and the SC2030 charge controller and the wire with the connectors. That system could handle up to 4 panels without any issues if you choose to upgrade. You could also get the Victron 15 or 20 amp MPPT , but you would be limited by the number of panels you could use.

Bottom line there are lots of combos depends on your budget but I would be investing in solar and not in upgrading the TV.

[cazual6]

Originally Posted by A W Warn

The tow vehicle has its own voltage regulation, to protect its electrical system. No need for duplication.

IMO, the charge wire from the tow vehicle is intended to maintain battery charge while at the same time traveling using fridge & furnace on propane. I think it is not intended to recharge the trailer's batteries while camping (though it will, but very slowly)

I concur

[waninae39]

you need to isolate the Tv from the trailers

some use a simple Shotcky diode

other use products like this
cyrix battery isolator

https://www.victronenergy.com/batter...tery-combiners

[A W Warn]

Originally Posted by waninae39

you need to isolate the Tv from the trailers
<<snip>>

Why?
In my 50+ years of towing all kinds of trailers with all kinds of tow vehicles I never have added anything to isolate the two vehicles' systems. I've never had an issue.

[rmkrum]

The reason is to be sure the tow vehicle will start the next morning. The other is based on the need for higher voltage to charge lithium batteries from a 12 volt truck. If the truck charge line is not properly isolated, the lithium batteries will actually charge the truck batteries under certain circumstances.
My Tacoma has a relay (I believe) that kills the charge line when the ignition is off, but that is insufficient protection when using lithium batteries. It does keep my truck battery from trying to charge the trailer batteries on cold nights...

[daleyocum]

Originally Posted by rmkrum

The reason is to be sure the tow vehicle will start the next morning. The other is based on the need for higher voltage to charge lithium batteries from a 12 volt truck. If the truck charge line is not properly isolated, the lithium batteries will actually charge the truck batteries under certain circumstances.
My Tacoma has a relay (I believe) that kills the charge line when the ignition is off, but that is insufficient protection when using lithium batteries. It does keep my truck battery from trying to charge the trailer batteries on cold nights...

I know my 2016 F150 has a lot of smarts built into it’s control of the charge pin on the trailer plug. It doesn’t even turn on that pin until you’ve stared the truck and put it back no gear. I suspect many other modern trucks are that way as well so a diode isn’t necessary in those cases.

I did need to use a Victron Orion to step up the voltage to the 14.4 volts my lithium batteries are looking for.