Wire Gauge Required Question

ken white wrote:
In order to test the various panel theories within this post, the test condition should have the panels connected to a fixed load and not to the controller.

As I stated earlier, the controller changes how the panel behaves so the data is skewed.

Example, if the batteries only need 100 watts and the controller consumes 10 watts of energy transferring this energy, then it will make sure the panel will only deliver 110 watts rather than its rated hypothetical 220 watts even though the panel could produce this value due to its direct sun exposure.

My field test method with PWM has been to get conditions where the panel is doing its Isc, measured at the panel junction box. Then compare those amps with what is showing on the Trimetric going into the battery.

If the battery is too full, then I run some lights to get enough "room" for the amps to show. EG, Isc is 8.2a. Batts are near full so only accepting 1a. Turn on four lights (12a) see -11a on Tri. (+1 for battery) Hook up the solar. Now see -3a. So 8a is reaching the batts from solar.

You need steady blue sky so no clouds keep screwing up the readings during the test.

So now what to do with MPPT, where you can get any old amps at the Trimetric depending on all that confusing stuff? You still need to get Isc on the panel junction box so you know it is doing its rating.

You get some amps at the battery but it won't be the Isc, it will be a mystery number. How do you know if that number is any good?

From this thread, I gather I should take the 230w panel rating (it is at Isc, so we are getting 230), subtract maybe 5% for all losses, so now we are at 218.5w. Now divide that by battery voltage of say 13 to get 16.8a expected. Compare that with what is showing on the Tri. After a few such tests, refine the percentage loss figure as you learn about how your set-up works.

But what about when the batts are not down, so you have to do the lights trick? What battery voltage do you use? The voltage seen with all those lights on is the loaded voltage.

My plan is to get the amps first and if anywhere near 17, I will be happy, and if it is near 15 I will be annoyed.

230w and PWM gets Isc of 230/130 x 8.2 = 14.5a. So all this fancy MPPT stuff better get me more than that! :) 17 isn't much more than 14.5 in real life anyway.