Solar Charge Controller

Vixen21 wrote:
Maybe I am Crazy But......
Are you sure you don't have that backwards? and that the wire size is much more important with PWM controllers than with the MPPT because of the higher voltages with the larger panels that use MPPT?

pianotuna wrote:
Hi,

One example is wire size. He doesn't understand that, for a PWM controller, any wire that is capable of legally carrying the maximum current from the panels is adequate.

It does, however, matter a LOT if an MPPT controller is to be used, because in that case voltage drop is important to avoid.

Vixen21 wrote:

pianotuna wrote:
Hi,

Because it is mostly a rant.

Vixen21 wrote:
Why not just read Handy Bob's Blog, it taught me a lot.

What information does he rant about that is wrong or incorrect?

Actually wire size matters more with MPPT.

With PWM your already throwing away power since the panel voltage is substantially above the battery voltage and output current is fixed (current out = current in). As long as the wire voltage drop with a PWM controller keeps you above about 14V or soit doesn't matter. (Assuming the controller is at the battery, which is where it should be for PWM or MPPT). typically with a 12V panel nominal output voltage is in the 18-20V range so you can have 4-6V of drop across the cable before you see much current change.

with a MPPT controller power out=power in, so any voltage drop between the panel and controller is a power drop to the controller and a reduction in output current.

I did experiments last winter and did a writeup. Short summary, even 100 ft of #10 wire didn't reduce the current from 160W of solar using a PWM controller. Using the 160W of solar (two 80W in parallel) with MPPT controller with the same 100ft resulted in a noticeable power loss comared to a 10ft cable. Still was higher current than PWM. Connecting the panels in series and MPPT resulted in a noticeble increase in current due to lower power loss in the cable. Power loss is related to the output current squared (I^2R) so two series panels cuts the current by 1/2 and the power loss by a factor of 4.

That said, solar panel output current drops with temperature, reducing the benefit of MPPT controllers in hot climate. I have MPPT to get the last bit of current to the batteries, but really on a cost benefit basis, for 100-200W panels IMHO a good PWM controller is more economical and more than adequate, and for the price difference you can almost buy an extra 80-100W panel now. So the potential 10-15% current gain with MPPT really is pretty spendy on a $/Amp basis.