Please help me with the big picture!

[PKUBIN]

Hi, All --

I'm going to be building my first squaredrop camper, roughly from Tony Latham's book. I'm a little confused about the the electrical system and could use an eagle's eye view.

Are the following assumptions correct?

1) There is a separate/dedicated circuit from the towing vehicle's 4-way plug, through the trailer (or attached to) the trailer's chassis to power its brake lights and turn signals

2) There is a separate/dedicated circuit from the trailer's own battery to power the internal electrics like lights, fan, TV, phone chargers, galley, etc.

3) The trailer's battery is charged by a shore line, RV-style plug, connected to land power. (I'm not planning any solar panels at this point).

4) Is there any charging connection between the towing vehicle and the trailer's battery? I realize there are different ways to do it, but what is most common and/or easier for a first build?

Thanks for your help!!!

[rjgimp]

Welcome to the asylum. Eagle eye? I happen to be an Eagle Scout, so I will give you "my" view.

1. Yes. There are four different colors which are dedicated to different functions. Brown is constant on for taillights. Yellow is left stop and turn. Green is right stop and turn. White is chassis negative return, commonly called "ground" although obviously it is not a true earth ground.

2. Yes. Of course, Your Mileage May Vary. If you are wanting higher draw things like television, microwave, coffee maker, air conditioning... you will need a LOT of battery and that will either get heavy or expensive.

3. Yes. Again, Your Mileage May Vary depending on how much stuff you want to power. If you only need to charge batteries and maybe have a few usb ports for a phone you can have a really simple shore power system that uses a standard 15A household plug and you would generally have a single circuit in your trailer. Many here have accomplished this with an extension cord and a power strip. The power will go to an AC to DC power converter to supply proper DC current to charge your trailer battery. If you have all those high draw electric toys you can choose to have a 30A system in your trailer. This is slightly more involved and has a special male plug that mates with one of the three female receptacles typically found on a campground shore power post. You could have as many as four circuits but the total of all the appliances you operate at one time can't exceed 30 amps.

4. Maybe. You can't really accomplish this within the 4 wire flat connector. You can do it within a 7-pin RV connector which also gives you the ability to have electric trailer brakes, but that isn't the best solution either. (If your trailer will be near or over 2000 pounds you might want trailer brakes anyway, and then you will need the 7-pin connector but that's a different conversation.) The better way to charge trailer batteries from the tow vehicle is with a separate connection using heavy cable (like the cable that connects to your vehicle starting battery) rather than the thin stuff you power trailer lights with. A connection like this is often made with an Anderson plug, but there are a handful of other great options.

Good luck and happy building!

[PKUBIN]

Thanks RG!

If I run a charging line from the towing vehicle, do I need to run an extra wire from the tow vehicle, or do they usually have a line near the rear bumper for additions like that?

[twisted lines]

Thanks RG!

If I run a charging line from the towing vehicle, do I need to run an extra wire from the tow vehicle, or do they usually have a line near the rear bumper for additions like that?

Most commonly if you want power you run it.

[JasenC]

1) There is a separate/dedicated circuit from the towing vehicle's 4-way plug, through the trailer (or attached to) the trailer's chassis to power its brake lights and turn signals

Yes

2) There is a separate/dedicated circuit from the trailer's own battery to power the internal electrics like lights, fan, TV, phone chargers, galley, etc.

Yes.

3) The trailer's battery is charged by a shore line, RV-style plug, connected to land power. (I'm not planning any solar panels at this point).

A twist lock style plug is more secure but a standard 3 prong is handy as you can use any 12g extension cord, but you can get adapter's as well. I'm getting a 160w foldable panel set up that I can set up where ever if I need to top off the battery.

4) Is there any charging connection between the towing vehicle and the trailer's battery? I realize there are different ways to do it, but what is most common and/or easier for a first build?

Like RJ said, you can charge from the TV with added hardware or as he said if you have a 7 pin which has a 12v lead to charge the camper battery.

[rjgimp]

Thanks RG!

If I run a charging line from the towing vehicle, do I need to run an extra wire from the tow vehicle, or do they usually have a line near the rear bumper for additions like that?

So, there are wires in the rear of your tow vehicle that will have power from the alternator flowing through them and if you tap into those wires that power will add juice to your trailer battery. In reality it isn't quite that simple.

Think of electricity flowing through wires like water flowing through pipes. In order to properly charge your trailer battery, particularly when it has been depleted, you need a lot of "flow" which is measured in amps. A given wire size can only handle a limited quantity of amps. Compare how much water flows out of your bathroom faucet vs. how much flows out of a fire hose vs. how much flows into or out of a municipal reservoir through a 4' diameter pipe to feed an entire city. A city water tower can be filled with a garden hose or a fire hose or a four foot water main. The garden hose is obviously not the most efficient option. The wires at the rear of your vehicle are designed to provide sufficient current to operate the tail and brake lights, but they are a bit like the garden hose. To most effectively and reliably charge your trailer battery, you might at least want a fire hose. Run a cable directly from the alternator. Because of the distance (20 feet or so) you will see some power loss. Figure out how many amps you need to feed into your trailer battery for efficient charging. Here is a page that discusses proper wire and cable size for running different amperages over a given distance. There is a handy chart if you scroll down some. For example, if you need a consistent 40 amps and it would take 20 feet of cable to get from the alternator output to the hitch, you should use 4AWG.

[tony.latham]

As others have said, there are two electrical systems. One for the chassis and one for the cabin.

If you want to charge the cabin battery you need a 10 AWG (fused) wire from your tow vehicle to a 7-pin plug at your bumper (and a subsequent 10 AWG to your battery). And that should probably only be used if installing a flooded lead-acid (marine) battery (not an AGM or a lithium battery) in your cabin. If you want to install an AGM or lithium battery, you should probably install a DC to DC charger.



Tony