8 Gauge Wire

otrfun wrote:

LaneW wrote:
. . . I think I need to run a 4awg . . .

What is the max *input* current rating for your dc to dc charger? This input current rating and the length of the cable run would determine which gauge cable is most appropriate for the input. You may find this voltage drop calculator helpful. IMO, a voltage drop of <2% is ideal, but up to 3% is acceptable.

We ran approx. 25 ft of 2 gauge cable from the engine compartment to the input of our dc to dc charger inside our truck camper. Our dc to dc charger is rated for 40a of *output* charge current. The *input* current (i.e., alternator load) will always be higher.

The 25 ft of 2 gauge cable nets us a ~3% voltage drop at 44-45a (nominal alternator load when producing 40a of output charge current). Yes, we could have used 25 ft of 4 gauge, but that would have increased voltage drop, reduced system efficiency, resulting in a higher load on the alternator. If we had used 4 gauge, the alternator load would have increased to approx. 50-55a (or almost 60a using 6 gauge) while still producing the same 40a of output charge current. If you're interested, Ohm's Law describes all these relationships in more detail.

If you're not concerned about the load (i.e., wear and tear) on the alternator, then using a smaller cable is fine. If you are concerned about reducing the load on the alternator, then using a larger cable is the way to go. Your choice.

Well, of course I am concerned about wear and tear on my alternator……..

What I am looking at installing is DCC30S 12V 30A Dual Input DC-DC On-Board Battery Charger with MPPT. I am looking at the specs but not finding the input current. I am still looking for that. But, and I’m sure I dont understand as well as you, I will be at a bit under 25 ft from truck batt to charger, which based on the specs I see online would be on the long end fog 6 awg, or safe with 4 awg. Right?