Checking in before I do something crazy... wiring 7 pin power source to house battery

[drodio]

I know there are other expo threads on this, but I just want to get a very specific answer to this before I go do something crazy that causes an explosion:

I recently bought an Adrenalin Trailer, and in it is the following wire, which says "Truck Charge Feed, Needs Diode." (see pic below)

I've run a multimeter against it and have verified that it's from the 7 pin trailer connector and is putting out 14.7 volts when the tow vehicle engine is running. The black line is the power line and the white line is the ground.

What I want to do is hook it up directly to the battery in the trailer to charge that battery -- i.e., hook the white wire to the negative battery terminal on the trailer battery, and the black wire to the positive terminal. Am I OK doing this?

Specifically, the reason I'm asking is because I want to make sure that feeding 14.7 volts to the trailer battery over a long period of time isn't going to over-charge it and cause it to explode. (For example let's say I drove cross-country and was feeding 14.7 volts for a week.) I'm pretty sure that the alternator of the tow vehicle will regulate the actual amperage so that it doesn't over-charge the battery, plus it's such a thin wire anyway it wouldn't be putting out lots of amps to the trailer battery in the first place.

PS I'm also assuming the "needs diode" is just referring to a battery isolator that would not drain the tow battery when the trailer is hooked up to the to vehicle but not running. I'm fine with just disconnecting the trailer from the tow vehicle when not moving for this one, so am I safe ignoring the "needs diode" part of that blue tape instruction?

Thanks! Here are a few other related pics:

 

[MountainD]

(White is hot, black is ground in most automotive systems) doesn't seem to hold true for trailers (as drodio will point out below. (Edited) Diodes in charging circuit is typically for the back feeding scenario you describe.

 

[Chris Boyd]

Checking in before I do something crazy... wiring 7 pin power source to house...

Definitely fuse the connection from the harness at the battery! Protects the battery and the wire going into the harness from anything that might cause a short. Since the harness is moving around, it's worth the safety margin.

I'd see what gauge the wire is and fuse it (or a resettable breaker) for what the wire is rated for at 12v

Not doing the diode would potentially allow for the trailer battery to back-flow to the truck, which might be desirable in certain situations. (Like the trailer being solar charged at camp and topping the truck if you're running a fridge in the truck). Yet another reason to fuse it.

 

[drodio]

Cool thx for the 411 guys... I'll let you know how it goes!

 

[drodio]

BTW re: "White is hot, black is ground in most automotive systems" pretty sure the white is ground and black is hot in this case, i.e., here's the wiring diagram:

 

[FEFF]

You could also use a 30 amp solar charge controller like this. It will isolate the batteries and charge your trailer battery properly.

http://www.amazon.com/Sunforce-6002...28&sr=8-8&keywords=sunforce+charge+controller

Mike

 

[97kurt]

I've seen people use these. I believe its just a diode and resistor.

http://www.amazon.com/dp/B004I9ZZFY...UTF8&colid=3JYXAF717NHD8&coliid=IAJXGZ7L9ZN7Z

 

[MountainD]

BTW re: "White is hot, black is ground in most automotive systems" pretty sure the white is ground and black is hot in this case, i.e., here's the wiring diagram:

GREAT observation. I never even suspected that trailers would reverse what auto's do. I looked at pin wiring diagrams for trailers and black is hot and white is ground-- I'll see if I can edit my previous statement (although black=ground still holds true for automotive wiring)...

 

[Nd4SpdSe]

Back-feed isn`t an issue with the vehicle running and the alternator running. Depending on your setup on how you want to connect it, you can do it a few ways.

If you`re running a battery isolator, there`s no need for the diode since it`s basically is one, and with a true isolator (some isolators are just solenoids, and call themselves isolators), not only does it solve the back-flow, but it also takes charge in balancing which battery need a charge, and the regulator in the alternator makes sure not to overcharge the battery, truck or trailer.

If you run just connected from the battery, the batteries will try to balance themselves out. Not really an isssue with the motor running and the alternator feeding them, but when the truck is off is where that could be an issue, where as you said, the truck can drain the trailer`s battery, or visa-versa. Diodes automatically take 0.7volts off the circuit, so you need a diode capable of handling the current. It`s been a long time so correct me if I`m wrong, but with 30A x 0.7v that the diode will take, that makes 21watts that the diode has to handle. The other option is to wire in a relay that turns on the trailer 12v power only when the truck is running.

On the 7-pin harness for the 12v, specs are about 30amps with a 10awg wire.