PWM controller question

Snowman9000 wrote:

BFL13 wrote:

Snowman9000 wrote:
I contend that you should use at least 17v, if not higher, for your voltage drop calculations. A quick run through that calculator shows that 50' of 10 gauge wire will present a voltage well into the 15's at the controller. Good enough for PWM in my book! Maybe the open circuit voltage of 22.x is really the one to use.

I only have a 100w portable kit, 6.x amps. I used 12-2 low voltage landscape wire from the big box hardware store. With Anderson Powerpole connectors at all junctions. You'd probably need to upgrade your tires to haul around all that 6 gauge wire. :)

The voltage on the wire from panel to controller with a "12v" is the battery voltage at the time. The IV curve V is battery voltage.

With "24v" the panel to MPPT controller (when in Bulk) wire is at Vmp maybe 30v, but the wire from controller to battery is "12v" battery voltage. I don't know what the "24v" panel voltage would be when the MPPT controller is in PWM.

If you have 17.7Vmp, 22.4Voc panels, and your wiring loses 1.5v, you've still got plenty of headroom with PWM to supply what the battery will take. Right, or not?

Not quite right. The voltage that matters is the voltage seen at the panel as a version of the battery voltage. The higher the battery voltage gets on the IV curve for that panel, the closer you get to the "knee" at about 15v where amps drop right off.

So 1.5v is a lot of difference. The panel will think it is at 15v when the battery is at 13.5 --oops. So get that voltage drop down to something a lot better.

Vmp is meaningless with 12v panel PWM. (Vmp is for MPPT.) Just look at the IV curve for what amps to expect vs battery voltage.

There is a point (controller high set point Vabs) at which the battery will be at high SOC and start tapering the acceptance amps, but this will be at a high SOC with such low amps as you get with solar. Meanwhile amps taper a bit along the IV curve too as battery voltage rises with rising SOC.

Scroll down to 14. Voltage Drop then go back to the wiring size chart earlier on to see how they try to get within those drops and confirm with the calculator linked in an earlier post

(was for my old shunt type controller (series type way better), but has a good explanation of voltage drop effect)

http://www.specialtyconcepts.com/SPECIALTY_CONCEPTS_PDF_FILES/ASC_INSTRUC_MANUAL.PDF