Resistance /is/ resistance. Voltage drop varies as a function of current:

Voltage drop = current X resistance.

As current goes up, voltage drop goes up. And, as you can see, the lower
the resistance, the lower the voltage drop.

For the 12V>12V charger -- the van is packed, I'm ready to go. I'm
standing here outside your door. I hate to wake you up to say ...

Wait -- that's a song.

Anyway, I'm ready to depart on a week-long camping trip and can't access
the place the charger is. And I continue to forget who makes it. You can
search the archives I suppose for postings from me around 2006, 2007.

But, yeah, it is a smart charger designed to charge deep cycle batteries
from the alternator or a charged 12V battery. It takes the output of the
alternator and does the whole thing: bulk (slowly, 7.5A limit),
absorption, and float. Floats the battery up at something like 14.7
volts. It works swell. Me likee.

--
Jack "Rocket j Squirrel" Elliott
Bend, Ore.
1984 Westfalia. A poor but proud people.
1971 "Ladybug"-brand utility trailer ca. 1972 from a defunct company in
San Clemente, Calif., now repurposed as The Westrailia.

Sent from my kitchen.

On 09/12/2011 09:25 PM, Steve Williams wrote:
> Hi,
>
> Thanks for the info. Now that I think about it a bit, I understand
> better that the "loss" is going to be in the high current draw
> situations. Initially, I figured resistance is resistance...
>
> What do you use for a 12VDC>12VDC charger? I assume it's a smart charger
> that is aware of the various (3?) stages of charging? It's funny you
> mention that because I was thinking of an inverter->12VDC "smart
> charger" would be way better than just pumping the alternator current at
> the battery. I never even thought of a 12VDC -> 12VDC charger.
>
> PLEASE no-one get into the charging logistics. ;-) There's lots of
> articles in the archives and I have copied many of them to read up on as
> my "next step".
>
> Thanks,
> Steve W.
>
> On 9/12/2011 5:14 PM, Rocket J Squirrel wrote:
>> Without knowing how much current is flowing from the alternator to the
>> batteries, it's impossible to know what the copper and other resistive
>> losses are. If the batteries are fully charged and there are no loads
>> (headlights off, etc.) then one should see a negligible voltage drop
>> even with skinny wire.
>>
>> But I'm no expert on these things, not seeing a reason to rework my
>> wiring to obtain slightly faster charging of my engine battery. With
>> my driving habits, it charges fine, as is.
>>
>> The 12VDC > 12VDC charger for my cabin battery limits current to 7.5
>> amperes, fast enough for my needs. Besides, my Trojan 130 Ah deep
>> cycle battery was a spendy little item and I like to baby it, perhaps
>> overmuch, by charging it like I discharge it: slowly.
>>
>