Switching alt power sources: 4-pin, 120v, etc

[marosell]

I'm building a 6x12 CT and plan on using the PD4045 (this would be powered by 3-pin twist lock connector, correct?). If I'm unable to connect to shore power, I'm curious if I can run the DC side off of the 4-pin connector coming from my truck. The running/brake/signal lights are already using this, and right now there is a single light in the camper that can use this as well. I plan on having the following items on DC power:

• MaxxAir Fan
• Cabin lights (LED puck)
• Possibly a stereo

Does anyone have a system for "switching over" between shore power and tow power?

For the AC side, if I have a standard 120v extension cord available, can I use this to power the 120 side if necessary? If so, how do you switch? I plan on having the following items on AC power:

• Microwave
• Fridge
• Receptacles
• AC Unit, 5,000 BTU

[Trebor English]

The 4 pin doesn't have an always on connection. The 7 pin connectors have a pin for that but usually it is only on when the engine is on. It would be reasonable to wire up your tow vehicle to have an always on connection. You would need to be careful to not run down your starter battery to the point it won't start.

[marosell]

The 4 pin doesn't have an always on connection. The 7 pin connectors have a pin for that but usually it is only on when the engine is on. It would be reasonable to wire up your tow vehicle to have an always on connection. You would need to be careful to not run down your starter battery to the point it won't start.

You're absolutely right. I have to turn on my truck parking lights to supply power to the trailer running lights, which I always turn on when I'm towing. I was just curious if there was an easy way to use DC power in the trailer, with the truck on and parking lights on, and how to switch between that and everything else.

[Ottsville]

Why not a 7 pin connector(or 6) and a battery on the trailer?

[troubleScottie]

Simple answer, no.

As stated a 4 pin connect does not have a DC positive or negative connection -- only the tail lights and turn signals. (tail light, turn/stop signals(right & left), common)

A 7 pin connector has all of the 4 pin plus brakes, reverse, DC+, running lights. The amperage limit is low, about 10 amps or lower depending on the length of the wire from the TV battery to the fixture.

You can run a separate power line (well pair of wires) like one might for a high power amplifier to the trailer to transfer higher amperage.

The major issues of using the DC+, as stated before, is that the towing vehicle (TV) must be running or at least the TV battery is connect. There is a danger of running down the TV battery and making driving out impossible.


In any case, look through the electrical sections, lots of information, lots of variations. Generally most advice is good. Your choice is limited by time, money and need.

[Aguyfromohio]

The conversations seems to be confounding "what is theoretically possible" with "what is practical and reliable".

Theoretically, the trailer 12 volt system is a plain old simple power bus. Apply voltage cross positive and negative and all loads anywhere can use it.
But speaking practically, the 4 pin light circuit has a tiny fuse on the tow vehicle and only tiny power available. Hardly better than a couple AA batteries. Why bother? Probably get better results sticking a power connector into the cigarette lighter socket and running those wires back. At least there you get a 20 amp fuse.

The 7 pin 10 amp supply is better, probably useful for topping up a battery while driving or running some LED lights while parked. But still pretty weak. Just enough power to drain the tow vehicle battery dead if we aren't careful trying to use it for lights when the tow vehicle is turned off.

On our rigs we are installing the high amp separate pair you describe. A pair of big 4 AWG wires from the tow vehicle battery out to the trailer. At the tow vehicle battery connections we have a 100 amp solenoid tied into the tow vehicle accessory circuit so the high power line goes dead when the vehicle is turned off. The 4 AWG wires should be able to carry 70 amps back to the trailer battery (15 feet) with only 0.52 volts drop. Our goal is to run our small 800 watt window air conditioner in the boondocks with the tow vehicle running as our generator if we really can't sleep. Separate connector plug for the power circuit using Anderson power connectors like this

[NorthEGPhoto]

I'm actually converting my 4 pin to a 7 pin and wiring a battery isolater in paralell. it would be pretty easy I think to do something similar with a manual switch if you wanted to run with the engine off. If I were doing it i'd probably put a switch in the engine compartment, or on the dashboard if you have easy access to the firewall, and then one more inside the trailer. That way you can be doubly sure you won't be stuck by accident somewhere.

(I may or may not also be wiring it so that anyone trying to tow without my custom built 7 pin cable might be in for a nasty surprise to their turn signals )