Trailer Charging by Vehicle

[Gerdo]

Another option for powered speakers is "self-powered". I have a pair of PC speakers that have some batteries in them. Mu music source is an IPod which if I need to recharge it I do thru a 12v outlet and usualy while driving.

[wannabefree]

There are a couple of good reasons to isolate your house battery from your vehicle, but the one that gets me going is I don't like being stuck.

You can charge batteries in parallel. When you do, the battery charger guys will tell you to use the same batteries of the same age and same size. This is because they share the charge circuit and if they are seriously mismatched you run the risk of damagine the weaker/lesser battery.

On the discharge side of things, when the batteries are connected in parallel they both get discharged. Here's where getting stuck comes into play. Discharge your car battery and the car won't start. Not good.

There are lots of ways to isolate the house from the car, ranked from easy/cheap to not-so-easy/expensive.

1) Don't connect your house to your car.
2) Unplug the house from the car when you camp.
3) Use a relay to disconnect automatically. Not a starter solenoid; these are not intended to be energized for long periods. Just use a cheap automotive relay. They cost under $5.
4) Use diodes. As mentioned, they exhibit the nasty .7V drop and can impact charging of the house battery, which will limit battery life. These cost ~$30 or build you rown for about $10.
5) Use a FET type isolator. Unlike diodes, no 0.7V drop, but they do have a small series resistance. This is normally not a problem, though it does exhibit a voltage drop under load. These cost $50-100. Or you could build your own for $?

[TinKicker]

With respect to an earlier poster (lost track who it was), I work in auto parts, and we service cables for golf carts and most often they use 4- or 6-gauge wire. 8- or 10-gauge should not be so big that you have problems with overcharging. I hope I understood the post correctly.
As far as the 4 to 7 pin adapters go, almost every auto parts store (AutoZone, Advance, Pep Boys, O'Reilley's, NAPA, etc.) carry them CHEAP.
Oh, one more thing...if you want to do it heavy-duty, there are constant-duty solenoids easily available in auto parts stores. Standard Ignition, the brand my store carries, has several. I'm sure NAPA can supply a similar part, but I don't think the other box stores get into the heavier parts like that.
Standard part # SS584 is a 12-volt 80amp continuous solenoid. It looks like an old Ford solenoid. They make others, but this one handles the most amperage. We sell this number quite often to a regional tree trimming company (Asplundh) for use on the Warn winches on their trucks. Very good part, but pricey...about $35 or thereabouts. But if you want a no-worry system, then that's the one.
Good luck with your design and happy trails!