8ga wire large enough?

[Vintage465]

Hi,
I am going to eventually add one more 150w Samlex panel to the existing array of 2 Samlex 150w panels. From the controller to the battery the trailer came equipped with an 8 gauge wire. Right around 10 feet long. Will this 8 gauge wire sufficiently carry the additional input from the third panel? Or should I attempt to replace it with a 4 or 6 gauge?

Thanks,

[CA_Traveler]

120VAC with a 3% drop is easily within the US utility standard of +-10% for appliances.

For 12V just using a % can be misleading. Let's take an example:

40A charger with 10' 8ga wire (one way) charging at 14.8V bulk rating of a flooded battery. That results in a 0.5V wire drop for 14.3V at the battery and a 3.4% voltage drop.

Or a 12.1V battery voltage with a 40A draw with 10' of 8ga wire. Now the appliance has 11.6V with a 4.15% voltage drop.

All is good on shore power with many hours to charge and a charger to maintain the battery with house loads. But if running the gen longer to charge or using solar then knowing the voltage/power losses should be considered along with the voltage to house loads.

Your mileage may vary. :):B

[camperguy99]

The charge acceptance rate varies considerable with applied voltage. 0.36 volts may mean you'll need days for the batteries to reach full charge. Not sure if the OP has 8 ga wire on the ground path? If so the problem is much worse. I have 720 watts of solar and i see about the same 0.36 volts drop at > 30 amps charge rate. And I have paralled two strands of 8 ga effectively making it 5 ga wire on both the live and ground wires. Wish I had even larger wire. I have seen my 40 MPPT controller max'd at at 40.0 amps after leveling and putting out all three slides.

[kellertx5er]

CA Traveler wrote:
I'll take exception to using the 40A wire rating. For 120V a 3% loss is small while 3% in a 12V system is much more significant for the battery voltage. It's all about acceptable voltage loss.

3% of 120V is 3.6V. 3% of 12V is 0.36V. How is this more significant on the 12V system? It is still 3%.

[memtb]

centerline, One of the many reasons for “winter” boondocking! ??

[centerline]

donn0128 wrote:
8ga wire is rated for 40A.
450 watts solar array is capable of 37A. So theoretically you would have sufficient cable. Of course 450A solar array is not likely to ever produce the full 37 amps. Unless you have a solar tracking package.

and are in the arctic on a very sunny summer day...

solar panels reach maximum efficiency with full sun and cold temperatures. as panel temps rise, efficiency drops, as it does with wiring, and batteries....

[CA_Traveler]

Vintage465 wrote:
Well, it sounds like 8ga. that came installed at the factory will work well enough with the 450w of solar. I don't tilt, or have any inverters or anything like that. I suppose one day I may go up to 4 each 6v batteries and the #6 or #4 wire could be of some benefit

Sounds like a plan. You can always upgrade the wiring including adding a parallel set of 8ga wires to the existing wires.

[Vintage465]

Right now I have a straight 30a Samlex Controller. Think maybe I should opt for a Steca MPPT 30a controller to get the most out of what we have............thoughts?

[memtb]

Personally, I’d opt for larger wiring.....less voltage drop and room for future expansion!

[Vintage465]

Well, it sounds like 8ga. that came installed at the factory will work well enough with the 450w of solar. I don't tilt, or have any inverters or anything like that. I suppose one day I may go up to 4 each 6v batteries and the #6 or #4 wire could be of some benefit

[CA_Traveler]

I went serial for smaller less involved wiring.

The other significant factor for me is the higher output available from partial shade due to the panels bypass diodes.

[RollandB]

When getting ready to do my solar install I planned to install 480w with three panels and wanted to have the ability to add another if needed. I went with a 4-2 duplex from the combiner box to controller. The cost difference isn’t much and the larger gauge helps reduce the voltage drop.

[WillT]

The 8 gauge will probably be fine but when I installed 3 panels for 540W I used 6 gauge. About 14 feet from roof combiner box to the controller. Then about 6 feet from controller to the batteries. Used 4/0 for the shunt to the batteries, about 5 feet. System works great but of course never really get the full output from the panels as only one is set up to tilt. But your 450W of solar with your wires should do OK even in the winter depending on number and type of batteries.

[Lwiddis]

I’d say 6 would be better over a 10 foot run. WindyNation tends to agree. https://www.windynation.com/jzv/inf/choosing-right-wire-size

[time2roll]

You can go about as big as you like with #8 wire. As you approach 30 amps you can start looking at going series mated to an MPPT controller. My 675 watts only puts out 7 amps to the controller (90 volts).