Charging while towing

[High Desert]

here's were things jumped the track;


wiring pos to pos, neg to neg is a parallel cicuit. 12V is maintained no matter how many batteries are connected.

wire pos to neg to pos to neg is a series circuit, and increases voltage each time a battery is added. Not a good idea for your TV as mentioned.

all you have to do is stay with a parallel circuit, you're good to go

[riverfront]

And the pictures and diagram Aunti M requested are??????????

[danlott]

This is my wiring plan. I will be able to charge while towing and also charge through the converter when hooked to 120V AC.



Sorry it is hard to see, had to fit within the picture size restraints.

Here it is sideways. It is a little bigger this way.



Dan

[rossjools]

I'd like to just add a little here. If you have 2x12V 40 AH batteries wired in parallel you will never get 24V as has been said earlier. What you will get is the equivalent of a 12V 80AH battery, given that both batteries are in the same condition. If you connect 2x12V 40AH batteries in series you will get 24V for sure. However you will only get a the equivalent of a 24V 40 AH battery given that both batteries are in the same condition.

An isolator or solenoid is a good idea if for no other reason than some of us forget to unplug the trailer. It's the same here in Australia where a lot of 4x4 owners wire in a second battery to run things like fridges etc even if they aren't towing a caravan or trailer. I once wired up a neighbour's 4x4 with a 3 position switch and 3 solenoids so that with the switch in one position the second battery was isolated from the main battery so it could be used at night for reading etc without flattening the vehicle battery. In one of the other positions the vehicle battery only was charged and in the third positon both batteries were being charged. When he started up in the morning he would switch to the main vehicle battery to make sure it was always getting a charge and always ready for service. After 20 minutes or so he would switch to the both position and both batteries would be getting a charge. He reported no problems with this set up until he sold the vehicle.

,
Ross.

[len19070]

I once wired up a neighbour's 4x4 with a 3 position switch and 3 solenoids so that with the switch in one position the second battery was isolated from the main battery so it could be used at night for reading etc without flattening the vehicle battery. In one of the other positions the vehicle battery only was charged and in the third positon both batteries were being charged. When he started up in the morning he would switch to the main vehicle battery to make sure it was always getting a charge and always ready for service. After 20 minutes or so he would switch to the both position and both batteries would be getting a charge. He reported no problems with this set up until he sold the vehicle.

,
Ross.

I hooked up a similar system on a truck camper I had.

The rig had 4 batteries.

2 starting, in the truck and 2 deep cycles in the camper.

Since during the week the truck was a work truck with an inverter starting the truck was a prime concern.

The truck itself had 2 starting batteries, A&B with an A, B or both switch, Starting was never a problem.

Driving I would charge up the 2 deep cycle batteries in the camper.

Either A or B or both.

When I was stopped I could run off of battery A or battery B.

I was so pleased with this system until I started thinking about it.

I only had "X" amount of stored amps. Didn't matter how I used them, that was all I had.

From then on I ran both deep cycle batteries at once.

Happy Trails

Len

[BirdDog1]

My owners guide says it hays a realy for trailer tow battery charge, so does that mean it is already connected to my 7 way?

[SomewhereInND]

There is one thing to be careful about when connecting/disconnecting trailer battery directly to tow vehicle (of course with a fuse) is power surges. BE CAREFUL WHEN UNHOOKING TRAILER CABLE WITH TOW VEHICLE RUNNING.

The tow vehicle alternater voltage limiter does not work very fast. If you have the vehicle running, with cable hooked up, and you disconnect it. Because the alternator all of a sudden does not have the load of the second battery, it may surge well past its intended output. Sometimes by 40-50 volts, this may burnout any 12 volt electronics that are hooked up.

[Starwatcher]

And a battery insolator, it will work to supply a battery in the trailer?

[fishfinder]

I have finished my trailer and now I want to hook up a charging line from my tow vehicle to the trailer battery. I plan on using an isolator/selenoid to protect my tow vehicle.

My trailer has an American AC/DC converter which is conected to the trailer battery. I am wondering if I need to disconect the trailer battery from the converter while charging with the tow vehicle or doesn't make any difference.

Any assistance would be appreciated.

Mike

[Nobody]

Mike, I too have the American converter. I don't disconnect the converter for charging while towing (I do have a main disconnect switch between the battery & the tow vehicle that I use when I don't need a charge). From what I've been told the converter 'sees' the voltage from your tow vehicle as a fully charged battery & just doesn't 'do' anything while the battery is being charged from the TV source.

[fishfinder]

Thanks Harvey. You have been the man since I started my build. Took her out on a short run and she pulled like a dream. All is well.

Mike

[danlott]

I am wondering if I need to disconect the trailer battery from the converter while charging with the tow vehicle or doesn't make any difference.

When you are charging with the tow vehicle you will not be connected to shore power. Without shore power the converter will not be able to charge the battery, so no problem to worry about.

Dan

[fishfinder]

Thanks Dan. What I was worrying about was the charge amperage from the TV running up the line to the converter. There is no isolation from the TV power to the converter in the TD when the TV charging line is connected.

Mike

[Von Pook]

Just wondering, does anyone think there would be a problem with running the TV battery to TD battery charging system, with a 20A fuse instead of a 30A fuse? Thank you

[mezz]

If in a pinch, could you charge your trailer battery with jumper cables off your vehicle?