Pv voltage drop

mountainman

With a 3% voltage drop on pwm using a panel vmp of 17.4.  20 foot on 8 gauge gives me 16.87 volts compared to a panel with 18.9 vmp on 70 foot run about  10% drop gives me 17 volts according to calculator voltage drop.net. If with pwm the battery regulates voltage and any thing above that is just lost would a 3% drop on a 18.9 panel give me more amps or watts compared to a 10% drop? 

mcgivor

The volt drop is due to the resistance of the conductors, which results in lost energy dissapated as heat, but in order to create heat there needs to be current to complete the equation, power equals voltage multiplied by current (P = V × I )  so if there was a 2 volt drop at 10 amps the power lost would be 20 watts, obviously as the volt drop increases so dose the power loss. This is why it's important to keep the volt drop to a minimum, regardless wether the PWM controller pulls the voltage down, the losses will still occur in the conductors resulting in lower output.

NANOcontrol

This question comes in conjunction with why panels are 18V and my battery is 12V. While you may loose 20W, It probably has absolutely  no effect on charging. It isn't going to effect charging until the voltage at the charger drops below what the battery needs. Lets say worst case is 1V loss in the charger, 2V in lead loss gets you to needing 17.5V at the panel.  Of course panel volts will drop when they get hot in the sun.  However, it is unlikely the battery will draw 10A at 14.5V unless you have an external load. With PWM you have no way to measure the voltage drop with just a meter as it will likely be pulsed.

mcgivor

So if that is the case, why not use the lightest gauge of wire available, with no current shouldn't be a problem, but wait the battery is discharged, example 11V and needs current, all of a sudden the current demand is 10A, hypothetically speaking, the wire now becomes a fuse, because it's incapable of supporting such currents, why?,volt drop rears it's ugly head, 

mountainman

The reason for my question I had to go 70 foot 9.5% drop on 8 gauge because of a pecan tree. Now a storm has taken the tree down.Anyway if I shorten to 35 ft and by parralleling 8 gauge cables I can get 2.5% drop. With 400 watts I'm seeing 308 watt 22 amp peaks with a 250 watt load. For short periods on cloudy days 340 and 24 amps.So can I expect a 7% increase in amps and watts. 9.5% -2.5%

mcgivor

There will be a reduction in losses which will improve overall output potential, the percentage of which will be determined on losses not overall production, reducing the volt drop will be benificial especially on hot days when panel voltage drops, 9.5% is too much 2.5% is much better, you may not notice a dramatic increase in overall output, but will have the peace of mind that in extreme conditions the system is designed to minimize potential problems associated with volt drop.

mountainman

Thanks mcgivor you gave me an  answer I can understand.

NANOcontrol

Do you? There is no technical reason to change the existing wiring.

mountainman

In winter there's no reason to change wire in summer I can see where voltage drop can be a concern when it's 100 degrees. A 2 volt drop puts me at 16.9 volts factor in temp coefficient of my panels and I can barely Equilize at 15.5

mountainman

Nano if I had to cut the tree the wind took down  or buy the biggest wire I wouldn't. But since I can double the wire I have at half the distance and get some extra watts by digging a hole. Time for the shovel 

mike95490

mountainman said:

Nano if I had to cut the tree the wind took down  or buy the biggest wire I wouldn't. But since I can double the wire I have at half the distance and get some extra watts by digging a hole. Time for the shovel 

Sounds like a lot of work to me. I'd be very tempted to save the $ of the wire, and just slap another panel in parallel.

mountainman

Problem is my 30 amp controller is maxed out at 400 watts . I'd have buy another controller and panel. My panels are on a pole I can remove with one bolt. Cut the wire I have and parralle them.then dig a 3 ft hole.

Plucka

I had solar output suddenly drop to 9.5 volts and no amps -was faulty mc4 connector

mountainman

Mine still had full voc 22.4 but only .9 amps