Who would have thought?

[HappiHenri]

AJMike - You are not missing anything. In RVs series connections are only usually used for connecting 2 6v batteries together in order to achieve a single 12v. When I had 4 Trojan 6v batteries I had 2 pairs each wired in series to effectively create 2 12v batteries. These 2 were then wired in parallel in order to then double the Amp Hour capacity. Like you said - if you have 12v batteries you want to only connect them in parallel.

In my experience it is usually marine applications which are designed to have 24v or even 48v systems. This is largely because they can work with smaller wire gauges over longer wire runs as many boats can easily be over 50' in length. By doubling the voltage you reduce the amperage load by 1/2, so smaller gauge wires will suffice. If you consider typical house wiring - 120v AC - you know how much power an 18 gauge lamp cord can carry - because the voltage is much higher.

As for amperage capacity of different types of wire - a 1/0 battery cable has the same electrical capacity as 1/0 welding cable. A 12 gauge solid core wire has the same as a 12 gauge stranded wire. The difference is that welding cable is composed of much smaller wires strands, making it more flexible. When working with these large cables flexibility becomes a big issue - it is physically so much easier to work with welding cable. But the electrical capacity is what the wire gauge refers to, not the type of wire.

[AJMike]

Originally Posted by HappiHenri

As for amperage capacity of different types of wire - a 1/0 battery cable has the same electrical capacity as 1/0 welding cable. A 12 gauge solid core wire has the same as a 12 gauge stranded wire. The difference is that welding cable is composed of much smaller wires strands, making it more flexible. When working with these large cables flexibility becomes a big issue - it is physically so much easier to work with welding cable. But the electrical capacity is what the wire gauge refers to, not the type of wire.

OK. So if I understand correctly you are saying that electric wire and welding cable are electrically the same given the same guage specification, but that they are constructed differently so that welding cable is more flexible.

I understand wire gauges to the extent that I know how gauge requirement varies for different currents - that is, if my wire connections for my 40 amp DC-DC charger are 8 ft or less than I can use 6 gauge, but it more than 8 ft and less than 16 ft I need 4 gauge. But I still don't understand how that relates to the x/y value given for welding cable. What is the gauge equivalent for 1/0?

I Googled welding cable 1/0 to see what it told me, but it was not very helpful in that it said that welding cable 1/0 is equivalent to wire 1/0. But I did not see anything that I understood that gave me an equivalence between the x/y specification and the z gauge specification. Is there some equivalence? Do I need to specify some specific welding cable x/y spec to make sure the guy uses the equivalent of 4 gauge wire? And is welding cable subject to the same length restrictions as regular wire? That is, is there a table specifying how many amps and how long a run for welding cable as there is for regular wire?

I really needed to pay more attention in shop class ...

[HappiHenri]

AJMike - Here is a link to a web sire describing wire gauges and amperage capacity. Please note that we have always referred to copper wires. Aluminum has a different capacity and is rarely used any more except in high end industrial applications.

https://www.powerstream.com/Wire_Size.htm

At the bottom of the chart is a calculating table which will show you voltage drop, by voltage, by wire gauge and by wire length. There are tons of wire gauge charts available all over the internet.

But in terms of RV applications it is better to use heaver gauges (to allow for current and future load capacities as well as upgrades to battery and charging systems) and to use welding wire due to it's flexibility and ease of use. There are many Youtube videos of RVers installing solar and lithium batteries, and once you see all that has to be added (solar controllers, fuses, shut-off switches, battery meters, shunts, etc, etc, ) you can understand why it is important to use a nice flexible wire, especially when having to route around tight spaces inside of RVs.

[AJMike]

Originally Posted by HappiHenri

https://www.powerstream.com/Wire_Size.htm

At the bottom of the chart is a calculating table which will show you voltage drop, by voltage, by wire gauge and by wire length. There are tons of wire gauge charts available all over the internet.

I checked the table and the voltage calculator at the bottom of the page. I have no doubt that it is all correct, but it left me even more puzzled than before.

My guess is that the previous installation had probably been close to the 8 foot limit with 6 AWG and my addition of perhaps 3 feet pushed it over what should be used, so I checked a 12 foot length at 6 AWG and a 12 foot length at 4 AWG and the difference is almost non-existent - 12 feet for 12 volts, 40 amps with 6 AWG delivers 11.61 volts while 12 feet for 12 volts, 40 amps with 4 AWG delivers 11.755 volts. That does not seem like much, although I suppose it could be enough of a difference for delicate electronic to cause issues. Still, I expected a bigger difference than 0.14 volts.

And there is no information about the equivalent gauge number for 0/1 welding cable.