Solar panel(s)

[richm]

Originally Posted by HABBERDABBER

Thank you for your response. I get it. I think my extension cords are 10' or 15', a fraction of the 50' you used. And I'm running a PWM, probably.

So what's the voltage drop for a 15', 12g cord? I'm too lazy to look it up, I guess.
And what I have has worked to charge the house batteries.
Voltage......Smoltage!

I can only find charts for solid wire, and extension cords are generally stranded, so the numbers below are an under-estimate. For a given gauge, voltage drop will be slightly higher for stranded than solid, since stranded has air gaps where solid does not.

20A via 15 feet of 12 gauge copper would be 1.19V.
20A via 15 feet of 12 gauge aluminum would be 1.95V.
See Voltage Drop Calculator

Here is the specific wire I am using for a 25 foot cable to handle 60A 12V with capability to scale up if needed. Low voltage drop. Low heat dissipation. This is a pair of 25 foot 6 gauge stranded copper cables:
https://www.amazon.com/dp/B00LIB8AQG...roduct_details


Another option is jumper cables. They are lower quality than welding cable, but are still rated for much high current than extension cables. It's possible a cheap pair of jumper cables would have much lower voltage drop than a 120V extensions cord.

[Brian B-P]

Originally Posted by richm

I can only find charts for solid wire, and extension cords are generally stranded, so the numbers below are an under-estimate. For a given gauge, voltage drop will be slightly higher for stranded than solid, since stranded has air gaps where solid does not.

Not really, because the gauge number indicates the cross-sectional area of conductor, not the outside diameter of the stranded bundle. That's where there are only voltage loss charts for solid wire - the values are the same for stranded wire so there's no need for additional charts.

[Mike G]

Originally Posted by richm

I can only find charts for solid wire, and extension cords are generally stranded, so the numbers below are an under-estimate. For a given gauge, voltage drop will be slightly higher for stranded than solid, since stranded has air gaps where solid does not.

20A via 15 feet of 12 gauge copper would be 1.19V.
20A via 15 feet of 12 gauge aluminum would be 1.95V.
See Voltage Drop Calculator

Here is the specific wire I am using for a 25 foot cable to handle 60A 12V with capability to scale up if needed. Low voltage drop. Low heat dissipation. This is a pair of 25 foot 6 gauge stranded copper cables:
https://www.amazon.com/dp/B00LIB8AQG...roduct_details


Another option is jumper cables. They are lower quality than welding cable, but are still rated for much high current than extension cables. It's possible a cheap pair of jumper cables would have much lower voltage drop than a 120V extensions cord.

It has been a while since I calculated my expected voltage drop, so I used the calculator you posted to refresh my memory. Thanks!


My panel is a 70W, and max output is roughly 4A @ 17V (I think it goes a tad higher, but good enough for the calc). Using a 14gauge 50' cord, the voltage drops to 15.74V. Still plenty to suit me.

[John in Santa Cruz]

The critical loss is between the charge controller and the battery. For an example a lead acid battery should be charged at about 13.8 v for the bulk phase, and if it's anything below 12.8 v it won't charge at all. So a 1-volt drop in the wiring from the controller to the battery at the charge current level would mean the difference between charging and not charging at all.

Voltage drop in the wire from the solar panel to the controller just reduces the overall efficiency, and also raises the floor for the minimum amount of sunlight needed to start a charge. Solar controllers will not increase the voltage they will only decrease it. A pwm controller will pass the same current just chopping the voltage down to the safe charging voltage, while an mppt controller will convert the extra voltage into more current. Like right now, my solar panel has a voltage around 38 volts and about 6 amps photovoltaic, the output of the mppt is 13.5 volts at 16.3 amps my battery is about 94% charged. This is a lithium iron phosphate battery. 11:00 a.m. daylight Time slightly hazy coastal sun in Coronado and I'm getting 225 Watts out of a quote 360 unquote watt panel. This past week is peaked at about 310 Watts, and given me about a kilowatt hour a day, but my batteries have never gone below 90% full