Charging while towing

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   OK, now I'm totally confused about what you are trying to accomplish. I thought it was to increase charging current while towing so you cam run the fridge on 12v? But you are saying that's not a problem. There is some kind of basic misunderstanding here I think. 
Lets try it this way.  Think in terms of energy flows. When you say you want to "top off" the trailer battery once you've parked, where is that energy coming from? Are you idling your tow vehicle and using the alternator to provide it? If so, just change the fridge over to propane and leave the 7 way connector attached. Problem solved. 

You can't charge from the tow vehicle without the alt running because that will remove energy from the TV battery and discharge it in short order.  If you are thinking that you can charge directly between the two batteries using the 7 way while at the same time charging via an inverter/charger in parallel that won't happen. The dc voltage will be established by the two batteries which are after all connected in parallel forming a single 12V buss.  The inverter/charger will just act like a load, basically a high tech heater sucking more energy from the system than its putting back in to the same buss its drawing from. You would have to disconnect the 12V connection between the two batteries and charge only through the inverter/charger. But why do that if you can charge directly far more efficiently just like you are doing while driving?

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offgrid Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: 23 Jul 2018 Online Status: Offline Posts: 5290	Topic: Charging while towing Posted: 19 Dec 2020 at 9:24am
	OK, now I'm totally confused about what you are trying to accomplish. I thought it was to increase charging current while towing so you cam run the fridge on 12v? But you are saying that's not a problem. There is some kind of basic misunderstanding here I think. Lets try it this way. Think in terms of energy flows. When you say you want to "top off" the trailer battery once you've parked, where is that energy coming from? Are you idling your tow vehicle and using the alternator to provide it? If so, just change the fridge over to propane and leave the 7 way connector attached. Problem solved. You can't charge from the tow vehicle without the alt running because that will remove energy from the TV battery and discharge it in short order. If you are thinking that you can charge directly between the two batteries using the 7 way while at the same time charging via an inverter/charger in parallel that won't happen. The dc voltage will be established by the two batteries which are after all connected in parallel forming a single 12V buss. The inverter/charger will just act like a load, basically a high tech heater sucking more energy from the system than its putting back in to the same buss its drawing from. You would have to disconnect the 12V connection between the two batteries and charge only through the inverter/charger. But why do that if you can charge directly far more efficiently just like you are doing while driving?
	1994 Chinook Concourse 1995 RV6A Experimental Aircraft 2015 Rpod 179 - sold

pedwards2932 Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: 21 Sep 2020 Online Status: Offline Posts: 337	Posted: 19 Dec 2020 at 9:45am
	I am charging with the alternator while driving. If I arrive at a campground with a hook up nothing is needed but to hook up. If I am doing an overnite with no hookup I can use the charger if needed. I don't see the complication.....this avoids needing a generator or solar panels. When I did it yesterday it charged very quickly so the battery didn't need a lot of charge. I can monitor the Escapes battery to see when it would need to be started......I honestly don't see the complication.....very similar to using a generator to charge up the battery.

offgrid Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: 23 Jul 2018 Online Status: Offline Posts: 5290	Posted: 19 Dec 2020 at 10:11am
	When you use a generator you are providing an external energy source. Ditto when you run the engine to use the alternator. Ditto again if you charge from a solar module. But if you attempt to charge the trailer battery from the tow vehicle battery you are merely moving energy from one battery to the other. It is a zero sum game, so completely different from using an external source. And the battery you are removing energy from has less capacity than the one you are moving it to. And if you use an inverter/charger you are moving it in a way that wastes about half of what you are moving. Its counter productive. If you want to be able to run the trailer from both batteries just leave the 7 way connected and that will happen without any waste. Just be careful not to run both batteries down and not be able to start the TV.
	1994 Chinook Concourse 1995 RV6A Experimental Aircraft 2015 Rpod 179 - sold

pedwards2932 Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: 21 Sep 2020 Online Status: Offline Posts: 337	Posted: 19 Dec 2020 at 10:24am
	Ok lets just say this works for me. When I overnite I will run the fridge on propane just don't want to do it while driving. When you hook up the 7 way and start the car the alternator reads the car battery voltage not the pod battery so it won't fully charge very well. Again my charger charged my battery pretty quickly....I have an old automatic charger so the amperage input rolled off as it reached full charge. I haven't spent any additional money and can top off my battery if needed. Again it works for me not sure what the argument is about.

offgrid Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: 23 Jul 2018 Online Status: Offline Posts: 5290	Posted: 19 Dec 2020 at 11:36am
	I prefer to run my fridge on 12V while towing also. But when we ask a question or propose something on a forum, we all need to expect questions and challenges, otherwise why ask? In this case the physics behind the energy flows is what it is, and it works the same for everyone. Of course its totally up to you what you do or don't do with information you get, its your rig. No argument from me.
	1994 Chinook Concourse 1995 RV6A Experimental Aircraft 2015 Rpod 179 - sold