Solar cable thru fridge vent

If you plan on 200W total wattage with MPPT, you can get a single 200W/24V panel - simpler wiring, no connections between panels. Simpler install, too - 4 brackets on the roof instead of 8. Single 24V panel typically costs less than 2*100W/12V.

8 AWG cable in "solar" MC4 version is not much thicker than 10 AWG. They are springy, though. Insulation is stiff. 8 AWG "welding cable" that you might see in some installs, is different.

But...

There is no need to go for #8 if you run 36V output to MPPT.
30ft long #10 will have 1.5% V-drop, #8 will have 1%. This is 0.5% difference.

With 200W array you will harvest 90 AH a day, at best. So, with #10 you will lose 0.5 AH a day more than with #10 (in fact, the difference is less than 0.5AH because your amps aren't always at maximum).

So, we are down to 0.2-0.3 AH daily difference btw #10 and #8 wire. This is NOTHING. You can run #12 all the way and will hardly see a difference either.

DAS26miles wrote:
When using those calculators, do you use 12 volts or 17 volts which is the output voltage from the panels to the controller.

Before getting into this, you need to tell what controller you have or going to have - PWM or MPPT. And - what panels, and how many. Or, at least - what you are going to achieve in terms of wattage and/or costs, and then we'll tell you what controller you need.

DAS26miles wrote:
The wires from the panel to the controller are the longest length. It's going to be the panel output right? And from the controller to the batteries is going to be the limit set in the controller like 14.6 volts bulk charge and 15.5 volts equalization????

Yes. This and few (several?) other limits.

DAS26miles wrote:
When using those calculators, do you use 12 volts or 17 volts which is the output voltage from the panels to the controller. The wires from the panel to the controller are the longest length. It's going to be the panel output right? And from the controller to the batteries is going to be the limit set in the controller like 14.6 volts bulk charge and 15.5 volts equalization????

With PWM, your amps from panel through the controller and on to the battery is the Isc of the panel or their total Isc if panels in parallel.

With MPPT you have a buck converter, so now the amps from panel to controller input is Imp and then from controller it is output amps to the battery. If the MPPT is doing "24-12" you might see nearly twice the amps after the controller as from the array.

DAS26miles wrote:
Doesn't Renogy have another sale after Christmas. I missed the Cyber-Monday deals.

Check Amazon... they have all the fittings and roof mounts etc...
Great price.. The controller is cheap enough and should work quite well.

http://www.amazon.com/Renogy-Watts-Volts-Monocrystalline-Solar/dp/B009Z6CW7O

The 100watt panels are 18.9Vmp... A good voltage to make Mppt work quite well.. Later, you could get a good MPPT controller... Lots of discussions here in Tech regarding the Pros/cons of MPPT v/s PWM....

Jim

DAS26miles wrote:
BigfootFord- Is that a 15 amp MPPT enough for the 200 watts. What are your panels putting out? Wow, 8 awg cable is thick and unmanageable. I have too many bends.

Max controller output amps I have seen is 13.5... Summer solstice aimed at the sun at about 2pm. So there is enough safety margin.

Panel Vmp is 23.2, Voc is 28.5, Isc is 5 amps and 4.35 Imp . A great panel for Mppt.

I was lucky running the 2 8ga wires. From fridge + - combine bars only about 8 ft only 1 difficult spot to bend was out of the fridge box into the internal cabinetry of the camper.

Jim

I went thru the side of my bathroom vent, took the vent apart and it led right into the ceiling void. Ran my wires thru the ceiling and into the rear of the pantry closet directly to the electrical compartment. Tied into the 12v IN from the batteries. My fridge is on the opposite side of the trailer so I would need to still run them thru the ceiling, this option gave me a shorter direct shot.

When using those calculators, do you use 12 volts or 17 volts which is the output voltage from the panels to the controller. The wires from the panel to the controller are the longest length. It's going to be the panel output right? And from the controller to the batteries is going to be the limit set in the controller like 14.6 volts bulk charge and 15.5 volts equalization????

Almot wrote:
Something I don't understand with this V-drop calculators. The one in BFL link says "single set of conductors, one-way length". If we have 2 leads of the same length, all is good. And, in panel wires this is usually the case - same or close length of Pos and Neg from panel to controller.

But, lets consider Pos 30ft and Neg 1 ft - ex, you bolted Neg to the frame when doing some trailer wiring - not necessarily panels. Should we still use one-way length, and if so, which one - 30ft or 1 ft? :)

What matters, of course, is the total wire length the electrons need to go through. If the calculator is set up for one-way wire length, you need to enter 30 + 1 = 31 feet in this case. If it's set up for a pair of wires, you enter half that length, or 15.5 feet.

In practice, it's almost certainly okay in this particular example to ignore the one foot pigtail as immaterial when compared with the 30' lead. A 3% error isn't going to alter your decision on what size wire is appropriate, partly because you can't buy 6.23 gauge wire.

Doesn't Renogy have another sale after Christmas. I missed the Cyber-Monday deals.

BigfootFord- Is that a 15 amp MPPT enough for the 200 watts. What are your panels putting out? Wow, 8 awg cable is thick and unmanageable. I have too many bends.