does 2 #8 wires equal one # 6 or #4 for added battery

Standard with a Lance camper installation is running a 8ga wire from the truck battery to the plug for the camper. 8ga is more than enough for charging the battery in the camper.

The heavy gauge wire used for the truck's battery/batteries is to enable a high current draw when the engine is being started. Very different demand than that of a 6-10 amp charging situation.

With a 40 foot total DC run the difference between 6ga and 8ga is only one tenth of a volt and going from 8ga to 4ga only increases the voltage by two tenths of a volt. Not going to be a measurable difference in charging time with 4ga versus 8ga in this situation.

I think you will be fine as well. Only issue you could have is if the truck camper battery is deeply discharged and then you "could" have problems. Make sure to install a fuse at the truck side, I assume the camper will have its own protection.

IMHO, it will be good enough. The second positive #8 wouldn't be any good without another negative anyway, or a separate wire to vehicle chassis ground. Another chassis ground would mean another connection to remember on top of your lights and the charge lead...

Great information guys thanks, based on further pondering of all the factors, I think I will just leave it with single #8...The 3 pin connector I am using between the truck and the TC will only accept no larger than #8 so that will always be an issue. I have yet to take a trip with the TC yet, so after a couple of runs If I have to upgrade then I will re-work it. And yes I am only looking to maintain the batt. for a full charge I can use a gennie and charger.

Hi,

The problem with parallel is that resistance has to be perfectly equal. It never is--so one wire ends up carrying more of the load than the other.

If you are pulling wire... get the right stuff and avoid the parallel.
NEC & RVIA frown on parallel connections.

I don't know what you plan to charge with, or the capacity of the batteries that you have, but charging will be based on the capacity of the battery, the depth of discharge and the available charge current. An 8 gauge wire is rated by NEC to 40 amps continuous in a bundle, 6 gauge is rated to 55 amps and 4 gauge is rated to 70 amps. These are pretty much very conservative ratings - some charts rate them to almost double, for use in open air or different types of wire, for example. So two 8 gauge wires have far more than double the capacity of a single 6 gauge, and slightly more than the capacity of one 4 gauge wire. The positive and negative wires need to be the same size, since they carry exactly the same current. This doesn't address voltage drop, which will vary depending on the actual current flowing and the length of the cable. Typically charging from a vehicle alternator is fairly low current, the battery voltage rises quite quickly and this reduced the amount of current that the alternator is regulated to produce. FWIW I have been charging batteries in TC's and trailers with a 10 gauge wire for years with complete success and satisfaction. You just don't want to think you can charge a completely discharged 500 AH battery this way, you can really just maintain the battery.

Brian

In this installation, where does the heavy gauge wire start and stop?

enblethen wrote:
A #8 stranded wire has a circular area of 16510. Doubled would be 33020.
A # 6 stranded has a circular mill area of 26240
A #4 stranded has a cicular mill of 41740
These are for building wire have seven strands.
So 2 #8s would be slightly more then one #6 but far less then 1 #4.
Yes you would be gaining as long as the negative is enlarged as well.
I would be using the #4 for both positve and negative.

You sir are correct,its been to many years, if you doubled the wire
it was in between by rule of thumb,8+8 was 6 not four

A #8 stranded wire has a circular area of 16510. Doubled would be 33020.
A # 6 stranded has a circular mill area of 26240
A #4 stranded has a cicular mill of 41740
These are for building wire have seven strands.
So 2 #8s would be slightly more then one #6 but far less then 1 #4.
Yes you would be gaining as long as the negative is enlarged as well.
I would be using the #4 for both positve and negative.