Dual Battery Hookup - Unconventional Wiring Question

The friendliest place on the web for anyone with an RV or an interest in RVing!
If you have answers, please help by responding to the unanswered posts.
See posts with no answers
Old Blevins

Old Blevins

Well-known member
Joined
Jul 14, 2012
Posts
542
Location
Brier, WA
Actually, two questions.  I have a friend who's adding a 2nd battery to his rig.  There isn't room near the first battery, but there is in the generator compartment at the other end of the rig.  He doesn't have a generator, but it does have heavy-duty cabling to the battery compartment up front which he will use to connect the batteries in parallel.

1. I've described the standard 2-battery connection layout, but he would need to add a new ground wire to the new battery to do that (it's a camper, so there's no common frame ground he can use).  He's asked what the drawback is of simply keeping pos & neg connections from his converter and his existing solar panel on the old battery with it connected in parallel to the new battery.  I think that means his old battery will get charged and will then equalize with the new battery (both batteries are actually new and identical).  Is that a problem?  Honestly, I couldn't tell him.  It seems like it would be inefficient, both for charging and for drawing on,  but how much?

2. He's gotten a new, portable solar panel with regulator that he wants to add to the system (he would connect this as needed directly to the "new" battery) and wants to know if there's any problem with the multiple charging systems.  I told him I thought the regulator on his new and the regulator on his existing solar should play nicely together.  Did I lie?

Thanks for any insights you can give me.

 
The problem is voltage drop along the wires leading to the distant second battery.  It only takes a few tenths of a volt to drastically change the amount of current flowing in or out of a battery, and the voltage lost when current flows through the long wires will restrict the current flowing in or out of the more distant battery.

In other words, the closer battery will do the majority of the work while the distant battery loafs along at less than it's rated capacity.
 
Thanks, Lou - that helps me give him an idea of the tradeoff.  Using a Voltage Drop Calculator I found online and assuming 16' of 8 gauge wire, you hit the nail on the head - he'd lose between 1/10 and 2/10 of a volt, depending on the amperage.  That's a significant loss and I suspect eventually the capacity of the batteries would get out of sync.

I'm assuming that the distance between the batteries is going to take its toll regardless of the wiring arrangement (though, under a standard wiring arrangement, they'd at least be charging and drawing at the same amounts as each other).  Any other drawbacks you can think of from not having the charge/draw connections hooked up to the pos of one battery and the neg of the other?
 
I agree the only issue is voltage drop on the wires connecting with batteries widely separated.

This thing about one battery charging faster.. Perhaps in BULK for reason cited above (Voltage drop in the wires) But under Absorption current is low enough they will return to lock step and both will hit FULL at the same time..  Still.. I would try to keep the batteries side by side for best retult.
 
Thanks, John.  I think having them next to each other is his first choice, too, but there's just no room.  At least there's no fatal flaw in his approach - not the best, but not the worst.
 
Old Blevins said:
Thanks, John.  I think having them next to each other is his first choice, too, but there's just no room.  At least there's no fatal flaw in his approach - not the best, but not the worst.
Click to expand...
Why not move both batteries to the generator compartment and use large enough wire to keep the voltage drop to a min?
 
You must log in or register to reply here.

Latest posts

Members online

Total: 1,248 (members: 28, guests: 1,220)

Forum statistics

Threads
131,931
Posts
1,387,714
Members
137,682
Latest member
duckyw7528
Back
Top Bottom