MEGAWATT 60-AMP INTRODUCTION

pnichols wrote:
"PWM is not wire size sensitive between panels and controller. MPPT is."

Don, would you please explain your comments above in more detail.

Based on electro-physics, the less the voltage drop (due to wire resistance) along the lowest voltage wire route (in this situation between the controller's output and the batteries) the better ... for minimum energy waste. So, shouldn't one ALWAYS have the controller - regardless of controller type - next to the battery(ies) to keep wire resistance, and hence losses, low along this path?

Based on the above, the higher voltage wire route (in this situation from the panels to the controller) can stand a bit more resistance if needed so as to have the panels out a distance from the RV and controller ... but still keeping even the wire in this path as large as practical.

I'm not talking about getting by good enough on the least expense, here. I'm talking about optimization of captured energy if one can spend just a bit more for a portable solar setup. I believe that the on-the-ball folks that put roof solar systems on their RVs try to comply with what I'm saying above. Why not take into account the same considerations when putting together a small portable system - where energy capture efficiency is just as, or more, important?

Here's the basics:

With 12V system, DC, you lose volts between panel and charge controller, based on wire gauge and length of wire. Not amps. There is already surplus "headroom" voltage coming from the panel, most of them put out from 22 to 18 or 17 Volts.

Your charge controller puts out 14.4V. It's highly unlikely you'll lose 3.6 to 2.6 volts between the panel and charge controller with any reasonable length of 14 gauge 15 amp rated wire when a 120 watt panel is putting out 6.6 Isc to 6.98 amps at 17 V.

Where you are concerned about the loss is between the charge controller once the voltage is dropped to 14.4V and the battery. This is where a short fat run of wire located as close to the battery, if your Vabs is NOT adjustable, becomes a concern. If your Vabs is adjustable at the controller, it's a non issue, you can add in Vabs at 1/10V at a time to compensate for V lost due to length of wire run to batteries from controller, within reason.

If this is a concern to you, pull the charge controller off the back of the solar panel and relocate it / mount it as close to the battery as possible without being exposed to charging fumes or gasses, with a permanent run of 12 Gauge wire and ring terminals within hopefully 3 or 4 feet of the batteries. Make the long run from the solar panel to the input side of the charge controller out of the 14 gauge 5 meter cord with quick disconnects to the input side of the charge controller.

Problem solved.

No need to make a mountain out of a mole hill.

If you need more assistance, Rjfishing can consult you on the details. He's run a bare bones basic charge controller on his rig with 190 Watts for a couple of years, same identical charge controller as on the back of my Solar Blvd 120W portable folding panel system. Works like a charm for him with 2 group 27 or 29 lead acid kmart or some such DC batteries.

This is the Jist of a portable panel system... K.I.S.S. and it works just fine. 14.4V is perfect and 100% of the Vabs requirements for most all AGM battery manufacturers.

I have been able to pull down 30 to 35 amps daily in Quartzsite, first week of January, 4 days straight, aiming the portable 120W panel 4x a day at the sun, Poloma area. Aiming it correctly in the AM until 1 pm or 2 pm is what yields the most amount of amps... By then, the battery was slowing down on taking a charge, and amps were dropping off, not because of the sun, but because the battery was getting full.

21 foot travel trailer, with a few hours of TV each night thrown in to the power usage. LED lights, refrig on, CO detector on, smoke alarm on, etc, and not worrying about if I left the lights on or off. LEDS help a lot with that.