8 Gauge Wire

LaneW wrote:
. . . 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?

According to the Renogy website, max rated input power for the DCC30S is 400w. Input voltage range is 13.2 - 16v (alternator voltage minus any voltage drop). Supposedly this unit is capable of up to 97% efficiency--impressive. Unfortunately, they don't state what conditions are necessary to obtain 97%, so efficiency could drop off significantly for other conditions. Based on these specs I'd guess-estimate input current would max out around 31a (current varies dependent on input/output voltage).

25 ft of 4 gauge would probably net you approx. 3% of voltage drop at 30-31a. This is based on the one-way distance (using the voltage calculator link I provided earlier). 3% should be fine. I wouldn't want it any higher.