Aux Battery Wiring, pt 2 (with pictures)

[rockandroll]

Currently my 25 amp power converter / charger is wired directly to the 7 pin trailer wire connector and will supply power only when the truck is on.

I would like to accomplish 2 things:

1. Add an AGM Battery to power the camper when the truck is not running
2. Charge the AGM camper battery while the truck is running

I plan on re-routing the 12v feed wire from the 7 pin (currently directly wired into the converter) directly to a battery separator as the "main battery". The camper battery is then wired to the separator as the 'aux battery'. Then the battery positive and ground are wired directly to the converter/charger. (Thanks UglyScout for the ground work)

Can you think of any concerns or better options?

The only one that comes to mind is potentially blowing out the alternator as it would be trying to charge 2 batteries at once.

 

[rockandroll]

Update...

I've researched and found "the common method" is to run it straight off the 7 pin to the battery with an inline fuse. You can charge your aux camper battery by directly wiring it into the 12v feed wire from the 7 pin (In my 2003 Tundra with the tow package (130 amp alt) you can draw up to (MAX) 30 amps to the 7pin. Probably closer to 18-20 after losses to the camper.

What about an isolator instead of a fuse? The isolator does not allow the trailer to discharge the truck battery, and vice versa. When the truck and trailer batteries are tied together in operation, the alternator sees one load, and the battery with the lower voltage, gets the most charge current until it equals the other battery, and then they get the same current until the alternator regulator cuts back.

The main disadvantage of doing it direct is the inconsistent charge to the battery as pos8 from wander the west pointed out in this post. Charging AGMs off a basic/direct alt out is usually too low for the bulk charge phase and too high for float charging. This isn't good for the battery. He I runs a 7.5amp DC/DC charge that does a 4 stage charge profile from a 10-15VDC input thus it makes up for line losses as well.

This DC/DC charger would go into my diagram in place of the isolator.

If there's anybody that's made it this far, would you think having the 4 stage charge profile @ 7.5amps would be more beneficial than having more amps (possibly double) via the direct method?



Some other useful posts for the searchers
http://www.tundrasolutions.com/forums/towing/73861-trailer-battery-charging/

http://www.tundrasolutions.com/forums/towing/4401-trailer-wiring/