Here's the deal......I need to run a 2AWG wire from the front of my pickup to my travel trailer for a DC to DC charger

I have a number of spools of 10g THHN wire from many past electrical jobs

I believe 6 #10 wies equals a #2AWG

Is it advisable to make up cables like this to run 30'.

I could twist all 6 wires together and then use plastic conduit to cover

Thanks!

The wires would carry different amounts of the current. You could have many more amperes in one of the 10awg than it could safely carry. Overheating to the point it melts insulation and takes out some of the other wires. Other bad things could happen. You can buy 60 feet of marine grade 2awg for less than $175. Your charging system would work a lot better.

Mickey Mouse! Do it right. 

If you manage to break or damage one, two or more wires, you will be forcing the other wires to carry more load than they are rated to carry.  Don't Disney Land engineer it....do it right.

Ken

Thanks! Good Advise..... My friend who is a head engineer at Disney World would get a kick out of your last statement.....Love it!

rb, while sure it can "work" its NOT how this retired electrical engineer would recommend. While it may not be exactly the same in your situation, when designing AC Power Distribution the use of parallel conductors (typically two, NOT six) was NOT allowed below certain wire gauge in case one conductor opened...…... 

Your use of large cable and quality low resistance connectors will greatly improve the charge balance when connecting multiple batteries in parallel CONGRATULATIONS.....I think we already discussed its best for balance if multiple batteries are the same type and design and size and even age?? Of course, when using a DC to DC Converter much of these concerns are not so applicable since it merely requires energy from Battery A and uses it to charge Battery B  and thus compensates.

John T 

Edited December 8 by oldjohnt

Most of the time extremely large conductors are used to minimize voltage loss, not to provide current carrying capacity.

A single #10 wire can carry 30 amps.   A single #8 wire can carry 50 amps.   The problem in low voltage applications usually isn't the wire's current capacity, it's the voltage loss along the wire dropping the voltage at the far end enough to restrict how much current the batteries can absorb.

20 ft. round trip (40 ft. total) of #8 AWG will lose 1.01 volts at 40 amps, so you'll have 11-13 volts at the far end under full load, depending on the alternator's charging voltage.  This is enough loss to cause problems charging a battery directly but not enough to effect the Renogy's performance.

According to the Renogy NG-DCC1212-40 manual it will work with input voltages as low as 8-10 volts so a single run of #8 wire is more than sufficient to feed it.

(I'm not an electrical engineer, just a radio tech who knows how circuits work).  ?

Edited December 8 by Lou Schneider

Good discussion Lou, so much depends on the quality and features of his DC to DC Converter and its INPUT requirements (how low yet still deliver sufficient regulated charging voltage and current) and OUTPUT charge parameters. Of course, I'd still advise the use of a single bigger gauge wire then a string of SIX conductors all wired in parallel (that's just strange at best)..... I cant in good faith recommend that (even if it will "work") but hey its his RV his money and his choice certainly not ours.

Fun sparky chatting with yall

John T

I hear ya! I'm ordering up 60' of 2AWG welding cable, solid copper. USA Made.....Will fuse it at the trucks battery with a 50amp Circuit Breaker and at the input to the trailers batteries with the same 50amp circuit breaker

With a 40a charger, do these numbers sound right?

rb, If you're using a 12 VDC to 12 VDC Converter/Charger that can deliver 40 max charging amps OUTPUT into an auxiliary 12 Volt battery, due to heat loss inefficiency it may (subject to design) require something under 50 amps being drawn from your primary battery...

So, a 50 Amp circuit breaker at your primary battery and another 50 amp at your auxiliary battery will "likely" work. If it trips at your primary battery (depends on converter draw current and time and time current curves of the breaker) you may have to use a bigger breaker, but that's still okay to protect 2 gauge wire.

Based on a max current of 50 amps, that #2 copper welding cable has more then adequate ampacity and Id venture a guess wont yield enough line voltage drop to require any bigger wire be used.

Hey I've seen far worse and more marginal wire size (like maybe 6 gauge use) so that #2 and 50 amps breakers at each battery WORKS FOR ME.

When designing a branch circuit you FIRST compute the maximum continuous current SECOND size the wire to have a minimum ampacity of 125%  of that, THIRD size the overcurrent protection device TO PROTECT THE WIRE not the device, that's another story. 

Its fun spending YOUR money lol

John T

I still recommend marine grade cables. Yes made in USA.  https://www.genuinedealz.com/

Totally agree on Marine Grade cable. Use nothing but tinned MG cable on my boat that lives in salt water. But on the truck and camper, all the other factory wire is simple copper. My last truck was 13 years old and 225,000 miles, up here in salted road New England, and all the auxiliary wring I installed for winch, truck camper, etc was fine.

If you use good wire routing and proper glue filled, shrink wrap,  protected connections....you will be good to go with quality welding cable.

The only thing wrong with jury rigging is it works.

Later,

J