Wire Gauge Required Question

NinerBikes wrote:

ktmrfs wrote:

smkettner wrote:
I would love for BFL13 to do an empirical test to quantify that 14 vs 10 loss.

For BFL's case run =30ft Imp=7.7A

for #10 cable power loss = 3.6W = about 0.27A at the output under max power. (0.06ohms x 7.7x7.7)

for #14 same conditions, power loss = 9 watts, about .75A under max conditions. (0.15ohms x 7.7x7.7) Note that #10 to #14 more than doubles the resistance. each increase/decrease by 3 wire sizes doubles or halves the resistance.

so depends on if 3/4 A is signficant to you.

How does this "theoretical" calculation compare to real world. Using the same method I calculated the power loss in output amps for my 160W panels connected in parallel vs. series for a 100ft run to the portable panels. Wire is #10 on one side #7 on the other side. (how?? well it is 30A Rv cord with one side being 2 #10's the other side being 1 #10 for calculations I used 150ft of #10 for total wire length)

doing the calculations power loss in a parallel connection was 12W about 1A. In a series connection power loss was calculated to be 3W or about 1/4 amp.

so.... last time I was out batteries near 50% SOC, using the trimetric in bright sun had them in parallel and looked at battery charging current, then switched to series and looked at battery charging current. Guess what, in series the current went up by real close to 3/4A. controller is a sunsaver 15 MPPT controller

So again how important is another 3/4A to you? Only you can decide.

For me, I don't have enough solar to ever get beyond bulk charging mode. 500AH of battery (4 T-125's) , only 160 W of solar. In fact I used the SW for the sunsaver to modify the charge profile to only use bulk and equalize mode and don't let bulk mode time out. So the "extra" 3/4 A or so most of the day is an extra 3/4A. It all helps.

In mid summer with sun all day I can recover 80-90% of a days power use. In the fall or under less sunny conditions (most common in our part of oregon) it's less. My goal is to maximize the days between firing up the generator.

Having 160W of solar and cost of your MPPT versus having 200 watts of 12v solar panel, and a 20 amp PWM by Morningstar, and 10 gauge wire. What is the gain or loss in Amps, and what is the cost difference?

This is assuming space is not at the limit currently, and you aren't running 10 ga over a 30 foot run from panel to controller, to batteries.

Can we assume $1.00 a watt per panel? One can spend a little more on watts and 12V panels that are larger, and will it offset the price of a Morningstar MPPT -15L at $230 plus shipping, vs a Morningstar PWM Sunsaver SSL 20L at $77.... well unless roof space is at a premium, the slightly more watt and larger panels, in a 2 panel application with PWM will be more cost effective, and produce more amps, will it not?

all very good questions and good analysis, especially if starting from scratch. In my case, since I use portable panels, size/weight for carrying, and storage space are much more important to me than in a fixed roof mount. Also, wanting to be able to go up to 100ft away from the trailer gets into power loss issues much more so than in a more typical use case. And I already had the two 80W panels anyway and was just looking to maximize output at a long distance.

At least there are lots of alternatives to pick and choose from to do what each individual thinks best fits their application.

choice between MPPT and PWM is kinda like the choice between 6V GC batteries and 12V batteries. First understand carefully your needs and what's important, then determine which choice best fits your needs and budget.