oversized wiring to charge controller

Almot wrote:
Still remains to be established whether they NEED #4, or even #6 :)

I rewired a friends rig that's running an Blue Sky mppt 30 amp 3024I. I figured 4 gauge because it was 20 ish feet. While buying parts from the solar dealer in Yuma he asked if we wanted him to calculate it for minimum volt drop. I said absolutely, you are the solar man. He said 4 gauge. He said he always recommends shooting for the lowest v drop and best practices in connections.

Yes his mppt is wired in parallel. He has mismatched panels so he cant run series. Well, he could but he would only be able to run his two 140's in series so as to stay under 46 volts. He also has a third 190 watt panel so all three are wired in parallel so he doesn't go over max voltage in series. He's still getting more by running it as pwm vs mppt on only 280 w. If he wanted to buy a 4th panel it would be even more of a mess as he couldn't series parallel them. From what I can tell in reading various sources it seems even more important to choose ALL the panels on day one when running mppt. I would also go with a high voltage mppt if using mppt. His system grew over time with poor guidance in the beginning. My friend was never shy with spending money but the original dealer installed 3 agm batteries (300ah), Magnum 2800 watt inverter with charger and ONE 140 watt panel and told him he'd be good. :)

Then someone told him to add a panel and they did another 140 in parallel. It was still wimpy so he added an 190 and the blue sky. Instead of the 190 they should have added 2 more 140's in series par for two strings of 280 at 40ish volts per string. While all that was going on it was wired with 6 g and several splices and a nice 14 g wire fuse holder that could also serve as a mini hand warmer. So he skimped and avoided his coffee maker etc.

Resistance= Distance, conductor size, and temperature of conductor, temp being the least of our worries.